1 | NAME |
1 | NAME |
2 | Coro - coroutine process abstraction |
2 | Coro - the only real threads in perl |
3 | |
3 | |
4 | SYNOPSIS |
4 | SYNOPSIS |
5 | use Coro; |
5 | use Coro; |
6 | |
6 | |
7 | async { |
7 | async { |
8 | # some asynchronous thread of execution |
8 | # some asynchronous thread of execution |
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9 | print "2\n"; |
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10 | cede; # yield back to main |
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11 | print "4\n"; |
9 | }; |
12 | }; |
10 | |
13 | print "1\n"; |
11 | # alternatively create an async coroutine like this: |
14 | cede; # yield to coro |
12 | |
15 | print "3\n"; |
13 | sub some_func : Coro { |
16 | cede; # and again |
14 | # some more async code |
17 | |
15 | } |
18 | # use locking |
16 | |
19 | my $lock = new Coro::Semaphore; |
17 | cede; |
20 | my $locked; |
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21 | |
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22 | $lock->down; |
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23 | $locked = 1; |
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24 | $lock->up; |
18 | |
25 | |
19 | DESCRIPTION |
26 | DESCRIPTION |
20 | This module collection manages coroutines. Coroutines are similar to |
27 | For a tutorial-style introduction, please read the Coro::Intro manpage. |
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28 | This manpage mainly contains reference information. |
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29 | |
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30 | This module collection manages continuations in general, most often in |
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31 | the form of cooperative threads (also called coros, or simply "coro" in |
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32 | the documentation). They are similar to kernel threads but don't (in |
21 | threads but don't run in parallel at the same time even on SMP machines. |
33 | general) run in parallel at the same time even on SMP machines. The |
22 | The specific flavor of coroutine used in this module also guarantees you |
34 | specific flavor of thread offered by this module also guarantees you |
23 | that it will not switch between coroutines unless necessary, at |
35 | that it will not switch between threads unless necessary, at |
24 | easily-identified points in your program, so locking and parallel access |
36 | easily-identified points in your program, so locking and parallel access |
25 | are rarely an issue, making coroutine programming much safer than |
37 | are rarely an issue, making thread programming much safer and easier |
26 | threads programming. |
38 | than using other thread models. |
27 | |
39 | |
28 | (Perl, however, does not natively support real threads but instead does |
40 | Unlike the so-called "Perl threads" (which are not actually real threads |
29 | a very slow and memory-intensive emulation of processes using threads. |
41 | but only the windows process emulation (see section of same name for |
30 | This is a performance win on Windows machines, and a loss everywhere |
42 | more details) ported to UNIX, and as such act as processes), Coro |
31 | else). |
43 | provides a full shared address space, which makes communication between |
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44 | threads very easy. And coro threads are fast, too: disabling the Windows |
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45 | process emulation code in your perl and using Coro can easily result in |
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46 | a two to four times speed increase for your programs. A parallel matrix |
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47 | multiplication benchmark (very communication-intensive) runs over 300 |
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48 | times faster on a single core than perls pseudo-threads on a quad core |
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49 | using all four cores. |
32 | |
50 | |
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51 | Coro achieves that by supporting multiple running interpreters that |
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52 | share data, which is especially useful to code pseudo-parallel processes |
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53 | and for event-based programming, such as multiple HTTP-GET requests |
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54 | running concurrently. See Coro::AnyEvent to learn more on how to |
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55 | integrate Coro into an event-based environment. |
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56 | |
33 | In this module, coroutines are defined as "callchain + lexical variables |
57 | In this module, a thread is defined as "callchain + lexical variables + |
34 | + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own |
58 | some package variables + C stack), that is, a thread has its own |
35 | callchain, its own set of lexicals and its own set of perls most |
59 | callchain, its own set of lexicals and its own set of perls most |
36 | important global variables. |
60 | important global variables (see Coro::State for more configuration and |
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61 | background info). |
37 | |
62 | |
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63 | See also the "SEE ALSO" section at the end of this document - the Coro |
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64 | module family is quite large. |
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65 | |
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66 | CORO THREAD LIFE CYCLE |
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67 | During the long and exciting (or not) life of a coro thread, it goes |
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68 | through a number of states: |
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69 | |
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70 | 1. Creation |
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71 | The first thing in the life of a coro thread is it's creation - |
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72 | obviously. The typical way to create a thread is to call the "async |
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73 | BLOCK" function: |
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74 | |
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75 | async { |
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76 | # thread code goes here |
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77 | }; |
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78 | |
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79 | You can also pass arguments, which are put in @_: |
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80 | |
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81 | async { |
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82 | print $_[1]; # prints 2 |
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83 | } 1, 2, 3; |
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84 | |
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85 | This creates a new coro thread and puts it into the ready queue, |
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86 | meaning it will run as soon as the CPU is free for it. |
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87 | |
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88 | "async" will return a Coro object - you can store this for future |
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89 | reference or ignore it - a thread that is running, ready to run or |
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90 | waiting for some event is alive on it's own. |
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91 | |
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92 | Another way to create a thread is to call the "new" constructor with |
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93 | a code-reference: |
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94 | |
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95 | new Coro sub { |
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96 | # thread code goes here |
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97 | }, @optional_arguments; |
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98 | |
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99 | This is quite similar to calling "async", but the important |
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100 | difference is that the new thread is not put into the ready queue, |
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101 | so the thread will not run until somebody puts it there. "async" is, |
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102 | therefore, identical to this sequence: |
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103 | |
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104 | my $coro = new Coro sub { |
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105 | # thread code goes here |
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106 | }; |
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107 | $coro->ready; |
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108 | return $coro; |
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109 | |
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110 | 2. Startup |
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111 | When a new coro thread is created, only a copy of the code reference |
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112 | and the arguments are stored, no extra memory for stacks and so on |
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113 | is allocated, keeping the coro thread in a low-memory state. |
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114 | |
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115 | Only when it actually starts executing will all the resources be |
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116 | finally allocated. |
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117 | |
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118 | The optional arguments specified at coro creation are available in |
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119 | @_, similar to function calls. |
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120 | |
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121 | 3. Running / Blocking |
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122 | A lot can happen after the coro thread has started running. Quite |
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123 | usually, it will not run to the end in one go (because you could use |
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124 | a function instead), but it will give up the CPU regularly because |
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125 | it waits for external events. |
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126 | |
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127 | As long as a coro thread runs, its Coro object is available in the |
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128 | global variable $Coro::current. |
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129 | |
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130 | The low-level way to give up the CPU is to call the scheduler, which |
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131 | selects a new coro thread to run: |
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132 | |
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133 | Coro::schedule; |
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134 | |
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135 | Since running threads are not in the ready queue, calling the |
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136 | scheduler without doing anything else will block the coro thread |
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137 | forever - you need to arrange either for the coro to put woken up |
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138 | (readied) by some other event or some other thread, or you can put |
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139 | it into the ready queue before scheduling: |
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140 | |
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141 | # this is exactly what Coro::cede does |
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142 | $Coro::current->ready; |
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143 | Coro::schedule; |
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144 | |
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145 | All the higher-level synchronisation methods (Coro::Semaphore, |
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146 | Coro::rouse_*...) are actually implemented via "->ready" and |
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147 | "Coro::schedule". |
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148 | |
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149 | While the coro thread is running it also might get assigned a |
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150 | C-level thread, or the C-level thread might be unassigned from it, |
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151 | as the Coro runtime wishes. A C-level thread needs to be assigned |
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152 | when your perl thread calls into some C-level function and that |
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153 | function in turn calls perl and perl then wants to switch |
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154 | coroutines. This happens most often when you run an event loop and |
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155 | block in the callback, or when perl itself calls some function such |
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156 | as "AUTOLOAD" or methods via the "tie" mechanism. |
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157 | |
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158 | 4. Termination |
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159 | Many threads actually terminate after some time. There are a number |
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160 | of ways to terminate a coro thread, the simplest is returning from |
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161 | the top-level code reference: |
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162 | |
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163 | async { |
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164 | # after returning from here, the coro thread is terminated |
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165 | }; |
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166 | |
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167 | async { |
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168 | return if 0.5 < rand; # terminate a little earlier, maybe |
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169 | print "got a chance to print this\n"; |
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170 | # or here |
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171 | }; |
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172 | |
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173 | Any values returned from the coroutine can be recovered using |
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174 | "->join": |
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175 | |
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176 | my $coro = async { |
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177 | "hello, world\n" # return a string |
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178 | }; |
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179 | |
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180 | my $hello_world = $coro->join; |
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181 | |
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182 | print $hello_world; |
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183 | |
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184 | Another way to terminate is to call "Coro::terminate", which at any |
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185 | subroutine call nesting level: |
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186 | |
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187 | async { |
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188 | Coro::terminate "return value 1", "return value 2"; |
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189 | }; |
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190 | |
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191 | Yet another way is to "->cancel" (or "->safe_cancel") the coro |
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192 | thread from another thread: |
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193 | |
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194 | my $coro = async { |
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195 | exit 1; |
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196 | }; |
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197 | |
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198 | $coro->cancel; # also accepts values for ->join to retrieve |
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199 | |
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200 | Cancellation *can* be dangerous - it's a bit like calling "exit" |
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201 | without actually exiting, and might leave C libraries and XS modules |
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202 | in a weird state. Unlike other thread implementations, however, Coro |
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203 | is exceptionally safe with regards to cancellation, as perl will |
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204 | always be in a consistent state, and for those cases where you want |
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205 | to do truly marvellous things with your coro while it is being |
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206 | cancelled - that is, make sure all cleanup code is executed from the |
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207 | thread being cancelled - there is even a "->safe_cancel" method. |
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208 | |
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209 | So, cancelling a thread that runs in an XS event loop might not be |
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210 | the best idea, but any other combination that deals with perl only |
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211 | (cancelling when a thread is in a "tie" method or an "AUTOLOAD" for |
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212 | example) is safe. |
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213 | |
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214 | Last not least, a coro thread object that isn't referenced is |
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215 | "->cancel"'ed automatically - just like other objects in Perl. This |
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216 | is not such a common case, however - a running thread is referencedy |
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217 | by $Coro::current, a thread ready to run is referenced by the ready |
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218 | queue, a thread waiting on a lock or semaphore is referenced by |
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219 | being in some wait list and so on. But a thread that isn't in any of |
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220 | those queues gets cancelled: |
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221 | |
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222 | async { |
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223 | schedule; # cede to other coros, don't go into the ready queue |
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224 | }; |
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225 | |
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226 | cede; |
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227 | # now the async above is destroyed, as it is not referenced by anything. |
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228 | |
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229 | A slightly embellished example might make it clearer: |
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230 | |
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231 | async { |
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232 | my $guard = Guard::guard { print "destroyed\n" }; |
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233 | schedule while 1; |
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234 | }; |
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235 | |
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236 | cede; |
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237 | |
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238 | Superficially one might not expect any output - since the "async" |
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239 | implements an endless loop, the $guard will not be cleaned up. |
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240 | However, since the thread object returned by "async" is not stored |
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241 | anywhere, the thread is initially referenced because it is in the |
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242 | ready queue, when it runs it is referenced by $Coro::current, but |
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243 | when it calls "schedule", it gets "cancel"ed causing the guard |
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244 | object to be destroyed (see the next section), and printing it's |
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245 | message. |
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246 | |
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247 | If this seems a bit drastic, remember that this only happens when |
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248 | nothing references the thread anymore, which means there is no way |
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249 | to further execute it, ever. The only options at this point are |
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250 | leaking the thread, or cleaning it up, which brings us to... |
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251 | |
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252 | 5. Cleanup |
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253 | Threads will allocate various resources. Most but not all will be |
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254 | returned when a thread terminates, during clean-up. |
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255 | |
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256 | Cleanup is quite similar to throwing an uncaught exception: perl |
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257 | will work it's way up through all subroutine calls and blocks. On |
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258 | it's way, it will release all "my" variables, undo all "local"'s and |
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259 | free any other resources truly local to the thread. |
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260 | |
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261 | So, a common way to free resources is to keep them referenced only |
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262 | by my variables: |
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263 | |
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264 | async { |
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265 | my $big_cache = new Cache ...; |
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266 | }; |
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267 | |
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268 | If there are no other references, then the $big_cache object will be |
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269 | freed when the thread terminates, regardless of how it does so. |
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270 | |
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271 | What it does "NOT" do is unlock any Coro::Semaphores or similar |
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272 | resources, but that's where the "guard" methods come in handy: |
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273 | |
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274 | my $sem = new Coro::Semaphore; |
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275 | |
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276 | async { |
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277 | my $lock_guard = $sem->guard; |
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278 | # if we return, or die or get cancelled, here, |
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279 | # then the semaphore will be "up"ed. |
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280 | }; |
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281 | |
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282 | The "Guard::guard" function comes in handy for any custom cleanup |
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283 | you might want to do (but you cannot switch to other coroutines from |
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284 | those code blocks): |
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285 | |
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286 | async { |
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287 | my $window = new Gtk2::Window "toplevel"; |
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288 | # The window will not be cleaned up automatically, even when $window |
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289 | # gets freed, so use a guard to ensure it's destruction |
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290 | # in case of an error: |
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291 | my $window_guard = Guard::guard { $window->destroy }; |
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292 | |
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293 | # we are safe here |
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294 | }; |
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295 | |
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296 | Last not least, "local" can often be handy, too, e.g. when |
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297 | temporarily replacing the coro thread description: |
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298 | |
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299 | sub myfunction { |
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300 | local $Coro::current->{desc} = "inside myfunction(@_)"; |
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301 | |
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302 | # if we return or die here, the description will be restored |
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303 | } |
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304 | |
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305 | 6. Viva La Zombie Muerte |
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306 | Even after a thread has terminated and cleaned up its resources, the |
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307 | Coro object still is there and stores the return values of the |
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308 | thread. |
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309 | |
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310 | When there are no other references, it will simply be cleaned up and |
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311 | freed. |
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312 | |
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313 | If there areany references, the Coro object will stay around, and |
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314 | you can call "->join" as many times as you wish to retrieve the |
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315 | result values: |
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316 | |
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317 | async { |
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318 | print "hi\n"; |
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319 | 1 |
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320 | }; |
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321 | |
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322 | # run the async above, and free everything before returning |
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323 | # from Coro::cede: |
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324 | Coro::cede; |
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325 | |
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326 | { |
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327 | my $coro = async { |
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328 | print "hi\n"; |
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329 | 1 |
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330 | }; |
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331 | |
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332 | # run the async above, and clean up, but do not free the coro |
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333 | # object: |
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334 | Coro::cede; |
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335 | |
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336 | # optionally retrieve the result values |
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337 | my @results = $coro->join; |
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338 | |
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339 | # now $coro goes out of scope, and presumably gets freed |
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340 | }; |
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341 | |
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342 | GLOBAL VARIABLES |
38 | $main |
343 | $Coro::main |
39 | This coroutine represents the main program. |
344 | This variable stores the Coro object that represents the main |
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345 | program. While you can "ready" it and do most other things you can |
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346 | do to coro, it is mainly useful to compare again $Coro::current, to |
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347 | see whether you are running in the main program or not. |
40 | |
348 | |
41 | $current (or as function: current) |
349 | $Coro::current |
42 | The current coroutine (the last coroutine switched to). The initial |
350 | The Coro object representing the current coro (the last coro that |
43 | value is $main (of course). |
351 | the Coro scheduler switched to). The initial value is $Coro::main |
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352 | (of course). |
44 | |
353 | |
45 | This variable is strictly *read-only*. It is provided for |
354 | This variable is strictly *read-only*. You can take copies of the |
46 | performance reasons. If performance is not essential you are |
355 | value stored in it and use it as any other Coro object, but you must |
47 | encouraged to use the "Coro::current" function instead. |
356 | not otherwise modify the variable itself. |
48 | |
357 | |
49 | $idle |
358 | $Coro::idle |
50 | A callback that is called whenever the scheduler finds no ready |
359 | This variable is mainly useful to integrate Coro into event loops. |
51 | coroutines to run. The default implementation prints "FATAL: |
360 | It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
52 | deadlock detected" and exits, because the program has no other way |
361 | is pretty low-level functionality. |
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362 | |
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363 | This variable stores a Coro object that is put into the ready queue |
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364 | when there are no other ready threads (without invoking any ready |
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365 | hooks). |
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366 | |
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367 | The default implementation dies with "FATAL: deadlock detected.", |
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368 | followed by a thread listing, because the program has no other way |
53 | to continue. |
369 | to continue. |
54 | |
370 | |
55 | This hook is overwritten by modules such as "Coro::Timer" and |
371 | This hook is overwritten by modules such as "Coro::EV" and |
56 | "Coro::Event" to wait on an external event that hopefully wake up a |
372 | "Coro::AnyEvent" to wait on an external event that hopefully wakes |
57 | coroutine so the scheduler can run it. |
373 | up a coro so the scheduler can run it. |
58 | |
374 | |
59 | Please note that if your callback recursively invokes perl (e.g. for |
375 | See Coro::EV or Coro::AnyEvent for examples of using this technique. |
60 | event handlers), then it must be prepared to be called recursively. |
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61 | |
376 | |
62 | STATIC METHODS |
377 | SIMPLE CORO CREATION |
63 | Static methods are actually functions that operate on the current |
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64 | coroutine only. |
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65 | |
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66 | async { ... } [@args...] |
378 | async { ... } [@args...] |
67 | Create a new asynchronous coroutine and return it's coroutine object |
379 | Create a new coro and return its Coro object (usually unused). The |
68 | (usually unused). When the sub returns the new coroutine is |
380 | coro will be put into the ready queue, so it will start running |
69 | automatically terminated. |
381 | automatically on the next scheduler run. |
70 | |
382 | |
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383 | The first argument is a codeblock/closure that should be executed in |
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384 | the coro. When it returns argument returns the coro is automatically |
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385 | terminated. |
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386 | |
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387 | The remaining arguments are passed as arguments to the closure. |
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388 | |
71 | See the "Coro::State::new" constructor for info about the coroutine |
389 | See the "Coro::State::new" constructor for info about the coro |
72 | environment. |
390 | environment in which coro are executed. |
73 | |
391 | |
74 | Calling "exit" in a coroutine will do the same as calling exit |
392 | Calling "exit" in a coro will do the same as calling exit outside |
75 | outside the coroutine. Likewise, when the coroutine dies, the |
393 | the coro. Likewise, when the coro dies, the program will exit, just |
76 | program will exit, just as it would in the main program. |
394 | as it would in the main program. |
77 | |
395 | |
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396 | If you do not want that, you can provide a default "die" handler, or |
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397 | simply avoid dieing (by use of "eval"). |
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398 | |
78 | # create a new coroutine that just prints its arguments |
399 | Example: Create a new coro that just prints its arguments. |
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400 | |
79 | async { |
401 | async { |
80 | print "@_\n"; |
402 | print "@_\n"; |
81 | } 1,2,3,4; |
403 | } 1,2,3,4; |
82 | |
404 | |
83 | async_pool { ... } [@args...] |
405 | async_pool { ... } [@args...] |
84 | Similar to "async", but uses a coroutine pool, so you should not |
406 | Similar to "async", but uses a coro pool, so you should not call |
85 | call terminate or join (although you are allowed to), and you get a |
407 | terminate or join on it (although you are allowed to), and you get a |
86 | coroutine that might have executed other code already (which can be |
408 | coro that might have executed other code already (which can be good |
87 | good or bad :). |
409 | or bad :). |
88 | |
410 | |
|
|
411 | On the plus side, this function is about twice as fast as creating |
|
|
412 | (and destroying) a completely new coro, so if you need a lot of |
|
|
413 | generic coros in quick successsion, use "async_pool", not "async". |
|
|
414 | |
89 | Also, the block is executed in an "eval" context and a warning will |
415 | The code block is executed in an "eval" context and a warning will |
90 | be issued in case of an exception instead of terminating the |
416 | be issued in case of an exception instead of terminating the |
91 | program, as "async" does. As the coroutine is being reused, stuff |
417 | program, as "async" does. As the coro is being reused, stuff like |
92 | like "on_destroy" will not work in the expected way, unless you call |
418 | "on_destroy" will not work in the expected way, unless you call |
93 | terminate or cancel, which somehow defeats the purpose of pooling. |
419 | terminate or cancel, which somehow defeats the purpose of pooling |
|
|
420 | (but is fine in the exceptional case). |
94 | |
421 | |
95 | The priority will be reset to 0 after each job, tracing will be |
422 | The priority will be reset to 0 after each run, tracing will be |
96 | disabled, the description will be reset and the default output |
423 | disabled, the description will be reset and the default output |
97 | filehandle gets restored, so you can change alkl these. Otherwise |
424 | filehandle gets restored, so you can change all these. Otherwise the |
98 | the coroutine will be re-used "as-is": most notably if you change |
425 | coro will be re-used "as-is": most notably if you change other |
99 | other per-coroutine global stuff such as $/ you need to revert that |
426 | per-coro global stuff such as $/ you *must needs* revert that |
100 | change, which is most simply done by using local as in " local $/ ". |
427 | change, which is most simply done by using local as in: "local $/". |
101 | |
428 | |
102 | The pool size is limited to 8 idle coroutines (this can be adjusted |
429 | The idle pool size is limited to 8 idle coros (this can be adjusted |
103 | by changing $Coro::POOL_SIZE), and there can be as many non-idle |
430 | by changing $Coro::POOL_SIZE), but there can be as many non-idle |
104 | coros as required. |
431 | coros as required. |
105 | |
432 | |
106 | If you are concerned about pooled coroutines growing a lot because a |
433 | If you are concerned about pooled coros growing a lot because a |
107 | single "async_pool" used a lot of stackspace you can e.g. |
434 | single "async_pool" used a lot of stackspace you can e.g. |
108 | "async_pool { terminate }" once per second or so to slowly replenish |
435 | "async_pool { terminate }" once per second or so to slowly replenish |
109 | the pool. In addition to that, when the stacks used by a handler |
436 | the pool. In addition to that, when the stacks used by a handler |
110 | grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will |
437 | grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also |
111 | also exit. |
438 | be destroyed. |
|
|
439 | |
|
|
440 | STATIC METHODS |
|
|
441 | Static methods are actually functions that implicitly operate on the |
|
|
442 | current coro. |
112 | |
443 | |
113 | schedule |
444 | schedule |
114 | Calls the scheduler. Please note that the current coroutine will not |
445 | Calls the scheduler. The scheduler will find the next coro that is |
115 | be put into the ready queue, so calling this function usually means |
446 | to be run from the ready queue and switches to it. The next coro to |
|
|
447 | be run is simply the one with the highest priority that is longest |
|
|
448 | in its ready queue. If there is no coro ready, it will call the |
|
|
449 | $Coro::idle hook. |
|
|
450 | |
|
|
451 | Please note that the current coro will *not* be put into the ready |
|
|
452 | queue, so calling this function usually means you will never be |
116 | you will never be called again unless something else (e.g. an event |
453 | called again unless something else (e.g. an event handler) calls |
117 | handler) calls ready. |
454 | "->ready", thus waking you up. |
118 | |
455 | |
119 | The canonical way to wait on external events is this: |
456 | This makes "schedule" *the* generic method to use to block the |
|
|
457 | current coro and wait for events: first you remember the current |
|
|
458 | coro in a variable, then arrange for some callback of yours to call |
|
|
459 | "->ready" on that once some event happens, and last you call |
|
|
460 | "schedule" to put yourself to sleep. Note that a lot of things can |
|
|
461 | wake your coro up, so you need to check whether the event indeed |
|
|
462 | happened, e.g. by storing the status in a variable. |
120 | |
463 | |
|
|
464 | See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for |
|
|
465 | callbacks. |
|
|
466 | |
|
|
467 | cede |
|
|
468 | "Cede" to other coros. This function puts the current coro into the |
|
|
469 | ready queue and calls "schedule", which has the effect of giving up |
|
|
470 | the current "timeslice" to other coros of the same or higher |
|
|
471 | priority. Once your coro gets its turn again it will automatically |
|
|
472 | be resumed. |
|
|
473 | |
|
|
474 | This function is often called "yield" in other languages. |
|
|
475 | |
|
|
476 | Coro::cede_notself |
|
|
477 | Works like cede, but is not exported by default and will cede to |
|
|
478 | *any* coro, regardless of priority. This is useful sometimes to |
|
|
479 | ensure progress is made. |
|
|
480 | |
|
|
481 | terminate [arg...] |
|
|
482 | Terminates the current coro with the given status values (see |
|
|
483 | cancel). The values will not be copied, but referenced directly. |
|
|
484 | |
|
|
485 | Coro::on_enter BLOCK, Coro::on_leave BLOCK |
|
|
486 | These function install enter and leave winders in the current scope. |
|
|
487 | The enter block will be executed when on_enter is called and |
|
|
488 | whenever the current coro is re-entered by the scheduler, while the |
|
|
489 | leave block is executed whenever the current coro is blocked by the |
|
|
490 | scheduler, and also when the containing scope is exited (by whatever |
|
|
491 | means, be it exit, die, last etc.). |
|
|
492 | |
|
|
493 | *Neither invoking the scheduler, nor exceptions, are allowed within |
|
|
494 | those BLOCKs*. That means: do not even think about calling "die" |
|
|
495 | without an eval, and do not even think of entering the scheduler in |
|
|
496 | any way. |
|
|
497 | |
|
|
498 | Since both BLOCKs are tied to the current scope, they will |
|
|
499 | automatically be removed when the current scope exits. |
|
|
500 | |
|
|
501 | These functions implement the same concept as "dynamic-wind" in |
|
|
502 | scheme does, and are useful when you want to localise some resource |
|
|
503 | to a specific coro. |
|
|
504 | |
|
|
505 | They slow down thread switching considerably for coros that use them |
|
|
506 | (about 40% for a BLOCK with a single assignment, so thread switching |
|
|
507 | is still reasonably fast if the handlers are fast). |
|
|
508 | |
|
|
509 | These functions are best understood by an example: The following |
|
|
510 | function will change the current timezone to |
|
|
511 | "Antarctica/South_Pole", which requires a call to "tzset", but by |
|
|
512 | using "on_enter" and "on_leave", which remember/change the current |
|
|
513 | timezone and restore the previous value, respectively, the timezone |
|
|
514 | is only changed for the coro that installed those handlers. |
|
|
515 | |
|
|
516 | use POSIX qw(tzset); |
|
|
517 | |
121 | { |
518 | async { |
122 | # remember current coroutine |
519 | my $old_tz; # store outside TZ value here |
123 | my $current = $Coro::current; |
|
|
124 | |
520 | |
125 | # register a hypothetical event handler |
521 | Coro::on_enter { |
126 | on_event_invoke sub { |
522 | $old_tz = $ENV{TZ}; # remember the old value |
127 | # wake up sleeping coroutine |
523 | |
128 | $current->ready; |
524 | $ENV{TZ} = "Antarctica/South_Pole"; |
129 | undef $current; |
525 | tzset; # enable new value |
130 | }; |
526 | }; |
131 | |
527 | |
132 | # call schedule until event occurred. |
528 | Coro::on_leave { |
133 | # in case we are woken up for other reasons |
529 | $ENV{TZ} = $old_tz; |
134 | # (current still defined), loop. |
530 | tzset; # restore old value |
135 | Coro::schedule while $current; |
531 | }; |
|
|
532 | |
|
|
533 | # at this place, the timezone is Antarctica/South_Pole, |
|
|
534 | # without disturbing the TZ of any other coro. |
|
|
535 | }; |
|
|
536 | |
|
|
537 | This can be used to localise about any resource (locale, uid, |
|
|
538 | current working directory etc.) to a block, despite the existance of |
|
|
539 | other coros. |
|
|
540 | |
|
|
541 | Another interesting example implements time-sliced multitasking |
|
|
542 | using interval timers (this could obviously be optimised, but does |
|
|
543 | the job): |
|
|
544 | |
|
|
545 | # "timeslice" the given block |
|
|
546 | sub timeslice(&) { |
|
|
547 | use Time::HiRes (); |
|
|
548 | |
|
|
549 | Coro::on_enter { |
|
|
550 | # on entering the thread, we set an VTALRM handler to cede |
|
|
551 | $SIG{VTALRM} = sub { cede }; |
|
|
552 | # and then start the interval timer |
|
|
553 | Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01; |
|
|
554 | }; |
|
|
555 | Coro::on_leave { |
|
|
556 | # on leaving the thread, we stop the interval timer again |
|
|
557 | Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0; |
|
|
558 | }; |
|
|
559 | |
|
|
560 | &{+shift}; |
136 | } |
561 | } |
137 | |
562 | |
138 | cede |
563 | # use like this: |
139 | "Cede" to other coroutines. This function puts the current coroutine |
564 | timeslice { |
140 | into the ready queue and calls "schedule", which has the effect of |
565 | # The following is an endless loop that would normally |
141 | giving up the current "timeslice" to other coroutines of the same or |
566 | # monopolise the process. Since it runs in a timesliced |
142 | higher priority. |
567 | # environment, it will regularly cede to other threads. |
143 | |
568 | while () { } |
144 | Returns true if at least one coroutine switch has happened. |
569 | }; |
145 | |
|
|
146 | Coro::cede_notself |
|
|
147 | Works like cede, but is not exported by default and will cede to any |
|
|
148 | coroutine, regardless of priority, once. |
|
|
149 | |
|
|
150 | Returns true if at least one coroutine switch has happened. |
|
|
151 | |
|
|
152 | terminate [arg...] |
|
|
153 | Terminates the current coroutine with the given status values (see |
|
|
154 | cancel). |
|
|
155 | |
570 | |
156 | killall |
571 | killall |
157 | Kills/terminates/cancels all coroutines except the currently running |
572 | Kills/terminates/cancels all coros except the currently running one. |
158 | one. This is useful after a fork, either in the child or the parent, |
|
|
159 | as usually only one of them should inherit the running coroutines. |
|
|
160 | |
573 | |
161 | # dynamic methods |
574 | Note that while this will try to free some of the main interpreter |
|
|
575 | resources if the calling coro isn't the main coro, but one cannot |
|
|
576 | free all of them, so if a coro that is not the main coro calls this |
|
|
577 | function, there will be some one-time resource leak. |
162 | |
578 | |
163 | COROUTINE METHODS |
579 | CORO OBJECT METHODS |
164 | These are the methods you can call on coroutine objects. |
580 | These are the methods you can call on coro objects (or to create them). |
165 | |
581 | |
166 | new Coro \&sub [, @args...] |
582 | new Coro \&sub [, @args...] |
167 | Create a new coroutine and return it. When the sub returns the |
583 | Create a new coro and return it. When the sub returns, the coro |
168 | coroutine automatically terminates as if "terminate" with the |
584 | automatically terminates as if "terminate" with the returned values |
169 | returned values were called. To make the coroutine run you must |
585 | were called. To make the coro run you must first put it into the |
170 | first put it into the ready queue by calling the ready method. |
586 | ready queue by calling the ready method. |
171 | |
587 | |
172 | See "async" and "Coro::State::new" for additional info about the |
588 | See "async" and "Coro::State::new" for additional info about the |
173 | coroutine environment. |
589 | coro environment. |
174 | |
590 | |
175 | $success = $coroutine->ready |
591 | $success = $coro->ready |
176 | Put the given coroutine into the ready queue (according to it's |
592 | Put the given coro into the end of its ready queue (there is one |
177 | priority) and return true. If the coroutine is already in the ready |
593 | queue for each priority) and return true. If the coro is already in |
178 | queue, do nothing and return false. |
594 | the ready queue, do nothing and return false. |
179 | |
595 | |
|
|
596 | This ensures that the scheduler will resume this coro automatically |
|
|
597 | once all the coro of higher priority and all coro of the same |
|
|
598 | priority that were put into the ready queue earlier have been |
|
|
599 | resumed. |
|
|
600 | |
|
|
601 | $coro->suspend |
|
|
602 | Suspends the specified coro. A suspended coro works just like any |
|
|
603 | other coro, except that the scheduler will not select a suspended |
|
|
604 | coro for execution. |
|
|
605 | |
|
|
606 | Suspending a coro can be useful when you want to keep the coro from |
|
|
607 | running, but you don't want to destroy it, or when you want to |
|
|
608 | temporarily freeze a coro (e.g. for debugging) to resume it later. |
|
|
609 | |
|
|
610 | A scenario for the former would be to suspend all (other) coros |
|
|
611 | after a fork and keep them alive, so their destructors aren't |
|
|
612 | called, but new coros can be created. |
|
|
613 | |
|
|
614 | $coro->resume |
|
|
615 | If the specified coro was suspended, it will be resumed. Note that |
|
|
616 | when the coro was in the ready queue when it was suspended, it might |
|
|
617 | have been unreadied by the scheduler, so an activation might have |
|
|
618 | been lost. |
|
|
619 | |
|
|
620 | To avoid this, it is best to put a suspended coro into the ready |
|
|
621 | queue unconditionally, as every synchronisation mechanism must |
|
|
622 | protect itself against spurious wakeups, and the one in the Coro |
|
|
623 | family certainly do that. |
|
|
624 | |
|
|
625 | $state->is_new |
|
|
626 | Returns true iff this Coro object is "new", i.e. has never been run |
|
|
627 | yet. Those states basically consist of only the code reference to |
|
|
628 | call and the arguments, but consumes very little other resources. |
|
|
629 | New states will automatically get assigned a perl interpreter when |
|
|
630 | they are transfered to. |
|
|
631 | |
|
|
632 | $state->is_zombie |
|
|
633 | Returns true iff the Coro object has been cancelled, i.e. it's |
|
|
634 | resources freed because they were "cancel"'ed, "terminate"'d, |
|
|
635 | "safe_cancel"'ed or simply went out of scope. |
|
|
636 | |
|
|
637 | The name "zombie" stems from UNIX culture, where a process that has |
|
|
638 | exited and only stores and exit status and no other resources is |
|
|
639 | called a "zombie". |
|
|
640 | |
180 | $is_ready = $coroutine->is_ready |
641 | $is_ready = $coro->is_ready |
181 | Return wether the coroutine is currently the ready queue or not, |
642 | Returns true iff the Coro object is in the ready queue. Unless the |
|
|
643 | Coro object gets destroyed, it will eventually be scheduled by the |
|
|
644 | scheduler. |
182 | |
645 | |
|
|
646 | $is_running = $coro->is_running |
|
|
647 | Returns true iff the Coro object is currently running. Only one Coro |
|
|
648 | object can ever be in the running state (but it currently is |
|
|
649 | possible to have multiple running Coro::States). |
|
|
650 | |
|
|
651 | $is_suspended = $coro->is_suspended |
|
|
652 | Returns true iff this Coro object has been suspended. Suspended |
|
|
653 | Coros will not ever be scheduled. |
|
|
654 | |
183 | $coroutine->cancel (arg...) |
655 | $coro->cancel (arg...) |
184 | Terminates the given coroutine and makes it return the given |
656 | Terminates the given Coro thread and makes it return the given |
185 | arguments as status (default: the empty list). Never returns if the |
657 | arguments as status (default: an empty list). Never returns if the |
186 | coroutine is the current coroutine. |
658 | Coro is the current Coro. |
187 | |
659 | |
|
|
660 | This is a rather brutal way to free a coro, with some limitations - |
|
|
661 | if the thread is inside a C callback that doesn't expect to be |
|
|
662 | canceled, bad things can happen, or if the cancelled thread insists |
|
|
663 | on running complicated cleanup handlers that rely on its thread |
|
|
664 | context, things will not work. |
|
|
665 | |
|
|
666 | Any cleanup code being run (e.g. from "guard" blocks, destructors |
|
|
667 | and so on) will be run without a thread context, and is not allowed |
|
|
668 | to switch to other threads. A common mistake is to call "->cancel" |
|
|
669 | from a destructor called by die'ing inside the thread to be |
|
|
670 | cancelled for example. |
|
|
671 | |
|
|
672 | On the plus side, "->cancel" will always clean up the thread, no |
|
|
673 | matter what. If your cleanup code is complex or you want to avoid |
|
|
674 | cancelling a C-thread that doesn't know how to clean up itself, it |
|
|
675 | can be better to "->throw" an exception, or use "->safe_cancel". |
|
|
676 | |
|
|
677 | The arguments to "->cancel" are not copied, but instead will be |
|
|
678 | referenced directly (e.g. if you pass $var and after the call change |
|
|
679 | that variable, then you might change the return values passed to |
|
|
680 | e.g. "join", so don't do that). |
|
|
681 | |
|
|
682 | The resources of the Coro are usually freed (or destructed) before |
|
|
683 | this call returns, but this can be delayed for an indefinite amount |
|
|
684 | of time, as in some cases the manager thread has to run first to |
|
|
685 | actually destruct the Coro object. |
|
|
686 | |
|
|
687 | $coro->safe_cancel ($arg...) |
|
|
688 | Works mostly like "->cancel", but is inherently "safer", and |
|
|
689 | consequently, can fail with an exception in cases the thread is not |
|
|
690 | in a cancellable state. Essentially, "->safe_cancel" is a "->cancel" |
|
|
691 | with extra checks before canceling. |
|
|
692 | |
|
|
693 | It works a bit like throwing an exception that cannot be caught - |
|
|
694 | specifically, it will clean up the thread from within itself, so all |
|
|
695 | cleanup handlers (e.g. "guard" blocks) are run with full thread |
|
|
696 | context and can block if they wish. The downside is that there is no |
|
|
697 | guarantee that the thread can be cancelled when you call this |
|
|
698 | method, and therefore, it might fail. It is also considerably slower |
|
|
699 | than "cancel" or "terminate". |
|
|
700 | |
|
|
701 | A thread is in a safe-cancellable state if it either hasn't been run |
|
|
702 | yet, or it has no C context attached and is inside an SLF function. |
|
|
703 | |
|
|
704 | The latter two basically mean that the thread isn't currently inside |
|
|
705 | a perl callback called from some C function (usually via some XS |
|
|
706 | modules) and isn't currently executing inside some C function itself |
|
|
707 | (via Coro's XS API). |
|
|
708 | |
|
|
709 | This call returns true when it could cancel the thread, or croaks |
|
|
710 | with an error otherwise (i.e. it either returns true or doesn't |
|
|
711 | return at all). |
|
|
712 | |
|
|
713 | Why the weird interface? Well, there are two common models on how |
|
|
714 | and when to cancel things. In the first, you have the expectation |
|
|
715 | that your coro thread can be cancelled when you want to cancel it - |
|
|
716 | if the thread isn't cancellable, this would be a bug somewhere, so |
|
|
717 | "->safe_cancel" croaks to notify of the bug. |
|
|
718 | |
|
|
719 | In the second model you sometimes want to ask nicely to cancel a |
|
|
720 | thread, but if it's not a good time, well, then don't cancel. This |
|
|
721 | can be done relatively easy like this: |
|
|
722 | |
|
|
723 | if (! eval { $coro->safe_cancel }) { |
|
|
724 | warn "unable to cancel thread: $@"; |
|
|
725 | } |
|
|
726 | |
|
|
727 | However, what you never should do is first try to cancel "safely" |
|
|
728 | and if that fails, cancel the "hard" way with "->cancel". That makes |
|
|
729 | no sense: either you rely on being able to execute cleanup code in |
|
|
730 | your thread context, or you don't. If you do, then "->safe_cancel" |
|
|
731 | is the only way, and if you don't, then "->cancel" is always faster |
|
|
732 | and more direct. |
|
|
733 | |
|
|
734 | $coro->schedule_to |
|
|
735 | Puts the current coro to sleep (like "Coro::schedule"), but instead |
|
|
736 | of continuing with the next coro from the ready queue, always switch |
|
|
737 | to the given coro object (regardless of priority etc.). The |
|
|
738 | readyness state of that coro isn't changed. |
|
|
739 | |
|
|
740 | This is an advanced method for special cases - I'd love to hear |
|
|
741 | about any uses for this one. |
|
|
742 | |
|
|
743 | $coro->cede_to |
|
|
744 | Like "schedule_to", but puts the current coro into the ready queue. |
|
|
745 | This has the effect of temporarily switching to the given coro, and |
|
|
746 | continuing some time later. |
|
|
747 | |
|
|
748 | This is an advanced method for special cases - I'd love to hear |
|
|
749 | about any uses for this one. |
|
|
750 | |
|
|
751 | $coro->throw ([$scalar]) |
|
|
752 | If $throw is specified and defined, it will be thrown as an |
|
|
753 | exception inside the coro at the next convenient point in time. |
|
|
754 | Otherwise clears the exception object. |
|
|
755 | |
|
|
756 | Coro will check for the exception each time a schedule-like-function |
|
|
757 | returns, i.e. after each "schedule", "cede", |
|
|
758 | "Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of |
|
|
759 | those functions (all that are part of Coro itself) detect this case |
|
|
760 | and return early in case an exception is pending. |
|
|
761 | |
|
|
762 | The exception object will be thrown "as is" with the specified |
|
|
763 | scalar in $@, i.e. if it is a string, no line number or newline will |
|
|
764 | be appended (unlike with "die"). |
|
|
765 | |
|
|
766 | This can be used as a softer means than either "cancel" or |
|
|
767 | "safe_cancel "to ask a coro to end itself, although there is no |
|
|
768 | guarantee that the exception will lead to termination, and if the |
|
|
769 | exception isn't caught it might well end the whole program. |
|
|
770 | |
|
|
771 | You might also think of "throw" as being the moral equivalent of |
|
|
772 | "kill"ing a coro with a signal (in this case, a scalar). |
|
|
773 | |
188 | $coroutine->join |
774 | $coro->join |
189 | Wait until the coroutine terminates and return any values given to |
775 | Wait until the coro terminates and return any values given to the |
190 | the "terminate" or "cancel" functions. "join" can be called |
776 | "terminate" or "cancel" functions. "join" can be called concurrently |
191 | concurrently from multiple coroutines. |
777 | from multiple threads, and all will be resumed and given the status |
|
|
778 | return once the $coro terminates. |
192 | |
779 | |
193 | $coroutine->on_destroy (\&cb) |
780 | $coro->on_destroy (\&cb) |
194 | Registers a callback that is called when this coroutine gets |
781 | Registers a callback that is called when this coro thread gets |
195 | destroyed, but before it is joined. The callback gets passed the |
782 | destroyed, that is, after it's resources have been freed but before |
196 | terminate arguments, if any. |
783 | it is joined. The callback gets passed the terminate/cancel |
|
|
784 | arguments, if any, and *must not* die, under any circumstances. |
197 | |
785 | |
|
|
786 | There can be any number of "on_destroy" callbacks per coro, and |
|
|
787 | there is currently no way to remove a callback once added. |
|
|
788 | |
198 | $oldprio = $coroutine->prio ($newprio) |
789 | $oldprio = $coro->prio ($newprio) |
199 | Sets (or gets, if the argument is missing) the priority of the |
790 | Sets (or gets, if the argument is missing) the priority of the coro |
200 | coroutine. Higher priority coroutines get run before lower priority |
791 | thread. Higher priority coro get run before lower priority coros. |
201 | coroutines. Priorities are small signed integers (currently -4 .. |
792 | Priorities are small signed integers (currently -4 .. +3), that you |
202 | +3), that you can refer to using PRIO_xxx constants (use the import |
793 | can refer to using PRIO_xxx constants (use the import tag :prio to |
203 | tag :prio to get then): |
794 | get then): |
204 | |
795 | |
205 | PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
796 | PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
206 | 3 > 1 > 0 > -1 > -3 > -4 |
797 | 3 > 1 > 0 > -1 > -3 > -4 |
207 | |
798 | |
208 | # set priority to HIGH |
799 | # set priority to HIGH |
209 | current->prio(PRIO_HIGH); |
800 | current->prio (PRIO_HIGH); |
210 | |
801 | |
211 | The idle coroutine ($Coro::idle) always has a lower priority than |
802 | The idle coro thread ($Coro::idle) always has a lower priority than |
212 | any existing coroutine. |
803 | any existing coro. |
213 | |
804 | |
214 | Changing the priority of the current coroutine will take effect |
805 | Changing the priority of the current coro will take effect |
215 | immediately, but changing the priority of coroutines in the ready |
806 | immediately, but changing the priority of a coro in the ready queue |
216 | queue (but not running) will only take effect after the next |
807 | (but not running) will only take effect after the next schedule (of |
217 | schedule (of that coroutine). This is a bug that will be fixed in |
808 | that coro). This is a bug that will be fixed in some future version. |
218 | some future version. |
|
|
219 | |
809 | |
220 | $newprio = $coroutine->nice ($change) |
810 | $newprio = $coro->nice ($change) |
221 | Similar to "prio", but subtract the given value from the priority |
811 | Similar to "prio", but subtract the given value from the priority |
222 | (i.e. higher values mean lower priority, just as in unix). |
812 | (i.e. higher values mean lower priority, just as in UNIX's nice |
|
|
813 | command). |
223 | |
814 | |
224 | $olddesc = $coroutine->desc ($newdesc) |
815 | $olddesc = $coro->desc ($newdesc) |
225 | Sets (or gets in case the argument is missing) the description for |
816 | Sets (or gets in case the argument is missing) the description for |
226 | this coroutine. This is just a free-form string you can associate |
817 | this coro thread. This is just a free-form string you can associate |
227 | with a coroutine. |
818 | with a coro. |
228 | |
819 | |
229 | This method simply sets the "$coroutine->{desc}" member to the given |
820 | This method simply sets the "$coro->{desc}" member to the given |
230 | string. You can modify this member directly if you wish. |
821 | string. You can modify this member directly if you wish, and in |
|
|
822 | fact, this is often preferred to indicate major processing states |
|
|
823 | that can then be seen for example in a Coro::Debug session: |
231 | |
824 | |
|
|
825 | sub my_long_function { |
|
|
826 | local $Coro::current->{desc} = "now in my_long_function"; |
|
|
827 | ... |
|
|
828 | $Coro::current->{desc} = "my_long_function: phase 1"; |
|
|
829 | ... |
|
|
830 | $Coro::current->{desc} = "my_long_function: phase 2"; |
|
|
831 | ... |
|
|
832 | } |
|
|
833 | |
232 | GLOBAL FUNCTIONS |
834 | GLOBAL FUNCTIONS |
233 | Coro::nready |
835 | Coro::nready |
234 | Returns the number of coroutines that are currently in the ready |
836 | Returns the number of coro that are currently in the ready state, |
235 | state, i.e. that can be switched to. The value 0 means that the only |
837 | i.e. that can be switched to by calling "schedule" directory or |
236 | runnable coroutine is the currently running one, so "cede" would |
838 | indirectly. The value 0 means that the only runnable coro is the |
237 | have no effect, and "schedule" would cause a deadlock unless there |
839 | currently running one, so "cede" would have no effect, and |
238 | is an idle handler that wakes up some coroutines. |
840 | "schedule" would cause a deadlock unless there is an idle handler |
|
|
841 | that wakes up some coro. |
239 | |
842 | |
240 | my $guard = Coro::guard { ... } |
843 | my $guard = Coro::guard { ... } |
241 | This creates and returns a guard object. Nothing happens until the |
844 | This function still exists, but is deprecated. Please use the |
242 | object gets destroyed, in which case the codeblock given as argument |
845 | "Guard::guard" function instead. |
243 | will be executed. This is useful to free locks or other resources in |
|
|
244 | case of a runtime error or when the coroutine gets canceled, as in |
|
|
245 | both cases the guard block will be executed. The guard object |
|
|
246 | supports only one method, "->cancel", which will keep the codeblock |
|
|
247 | from being executed. |
|
|
248 | |
|
|
249 | Example: set some flag and clear it again when the coroutine gets |
|
|
250 | canceled or the function returns: |
|
|
251 | |
|
|
252 | sub do_something { |
|
|
253 | my $guard = Coro::guard { $busy = 0 }; |
|
|
254 | $busy = 1; |
|
|
255 | |
|
|
256 | # do something that requires $busy to be true |
|
|
257 | } |
|
|
258 | |
846 | |
259 | unblock_sub { ... } |
847 | unblock_sub { ... } |
260 | This utility function takes a BLOCK or code reference and "unblocks" |
848 | This utility function takes a BLOCK or code reference and "unblocks" |
261 | it, returning the new coderef. This means that the new coderef will |
849 | it, returning a new coderef. Unblocking means that calling the new |
262 | return immediately without blocking, returning nothing, while the |
850 | coderef will return immediately without blocking, returning nothing, |
263 | original code ref will be called (with parameters) from within its |
851 | while the original code ref will be called (with parameters) from |
264 | own coroutine. |
852 | within another coro. |
265 | |
853 | |
266 | The reason this function exists is that many event libraries (such |
854 | The reason this function exists is that many event libraries (such |
267 | as the venerable Event module) are not coroutine-safe (a weaker form |
855 | as the venerable Event module) are not thread-safe (a weaker form of |
268 | of thread-safety). This means you must not block within event |
856 | reentrancy). This means you must not block within event callbacks, |
269 | callbacks, otherwise you might suffer from crashes or worse. |
857 | otherwise you might suffer from crashes or worse. The only event |
|
|
858 | library currently known that is safe to use without "unblock_sub" is |
|
|
859 | EV (but you might still run into deadlocks if all event loops are |
|
|
860 | blocked). |
|
|
861 | |
|
|
862 | Coro will try to catch you when you block in the event loop |
|
|
863 | ("FATAL:$Coro::idle blocked itself"), but this is just best effort |
|
|
864 | and only works when you do not run your own event loop. |
270 | |
865 | |
271 | This function allows your callbacks to block by executing them in |
866 | This function allows your callbacks to block by executing them in |
272 | another coroutine where it is safe to block. One example where |
867 | another coro where it is safe to block. One example where blocking |
273 | blocking is handy is when you use the Coro::AIO functions to save |
868 | is handy is when you use the Coro::AIO functions to save results to |
274 | results to disk. |
869 | disk, for example. |
275 | |
870 | |
276 | In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
871 | In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
277 | when creating event callbacks that want to block. |
872 | when creating event callbacks that want to block. |
278 | |
873 | |
|
|
874 | If your handler does not plan to block (e.g. simply sends a message |
|
|
875 | to another coro, or puts some other coro into the ready queue), |
|
|
876 | there is no reason to use "unblock_sub". |
|
|
877 | |
|
|
878 | Note that you also need to use "unblock_sub" for any other callbacks |
|
|
879 | that are indirectly executed by any C-based event loop. For example, |
|
|
880 | when you use a module that uses AnyEvent (and you use |
|
|
881 | Coro::AnyEvent) and it provides callbacks that are the result of |
|
|
882 | some event callback, then you must not block either, or use |
|
|
883 | "unblock_sub". |
|
|
884 | |
|
|
885 | $cb = rouse_cb |
|
|
886 | Create and return a "rouse callback". That's a code reference that, |
|
|
887 | when called, will remember a copy of its arguments and notify the |
|
|
888 | owner coro of the callback. |
|
|
889 | |
|
|
890 | See the next function. |
|
|
891 | |
|
|
892 | @args = rouse_wait [$cb] |
|
|
893 | Wait for the specified rouse callback (or the last one that was |
|
|
894 | created in this coro). |
|
|
895 | |
|
|
896 | As soon as the callback is invoked (or when the callback was invoked |
|
|
897 | before "rouse_wait"), it will return the arguments originally passed |
|
|
898 | to the rouse callback. In scalar context, that means you get the |
|
|
899 | *last* argument, just as if "rouse_wait" had a "return ($a1, $a2, |
|
|
900 | $a3...)" statement at the end. |
|
|
901 | |
|
|
902 | See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
|
|
903 | example. |
|
|
904 | |
|
|
905 | HOW TO WAIT FOR A CALLBACK |
|
|
906 | It is very common for a coro to wait for some callback to be called. |
|
|
907 | This occurs naturally when you use coro in an otherwise event-based |
|
|
908 | program, or when you use event-based libraries. |
|
|
909 | |
|
|
910 | These typically register a callback for some event, and call that |
|
|
911 | callback when the event occured. In a coro, however, you typically want |
|
|
912 | to just wait for the event, simplyifying things. |
|
|
913 | |
|
|
914 | For example "AnyEvent->child" registers a callback to be called when a |
|
|
915 | specific child has exited: |
|
|
916 | |
|
|
917 | my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... }); |
|
|
918 | |
|
|
919 | But from within a coro, you often just want to write this: |
|
|
920 | |
|
|
921 | my $status = wait_for_child $pid; |
|
|
922 | |
|
|
923 | Coro offers two functions specifically designed to make this easy, |
|
|
924 | "rouse_cb" and "rouse_wait". |
|
|
925 | |
|
|
926 | The first function, "rouse_cb", generates and returns a callback that, |
|
|
927 | when invoked, will save its arguments and notify the coro that created |
|
|
928 | the callback. |
|
|
929 | |
|
|
930 | The second function, "rouse_wait", waits for the callback to be called |
|
|
931 | (by calling "schedule" to go to sleep) and returns the arguments |
|
|
932 | originally passed to the callback. |
|
|
933 | |
|
|
934 | Using these functions, it becomes easy to write the "wait_for_child" |
|
|
935 | function mentioned above: |
|
|
936 | |
|
|
937 | sub wait_for_child($) { |
|
|
938 | my ($pid) = @_; |
|
|
939 | |
|
|
940 | my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb); |
|
|
941 | |
|
|
942 | my ($rpid, $rstatus) = rouse_wait; |
|
|
943 | $rstatus |
|
|
944 | } |
|
|
945 | |
|
|
946 | In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
|
|
947 | you can roll your own, using "schedule" and "ready": |
|
|
948 | |
|
|
949 | sub wait_for_child($) { |
|
|
950 | my ($pid) = @_; |
|
|
951 | |
|
|
952 | # store the current coro in $current, |
|
|
953 | # and provide result variables for the closure passed to ->child |
|
|
954 | my $current = $Coro::current; |
|
|
955 | my ($done, $rstatus); |
|
|
956 | |
|
|
957 | # pass a closure to ->child |
|
|
958 | my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
|
|
959 | $rstatus = $_[1]; # remember rstatus |
|
|
960 | $done = 1; # mark $rstatus as valid |
|
|
961 | $current->ready; # wake up the waiting thread |
|
|
962 | }); |
|
|
963 | |
|
|
964 | # wait until the closure has been called |
|
|
965 | schedule while !$done; |
|
|
966 | |
|
|
967 | $rstatus |
|
|
968 | } |
|
|
969 | |
279 | BUGS/LIMITATIONS |
970 | BUGS/LIMITATIONS |
280 | - you must make very sure that no coro is still active on global |
971 | fork with pthread backend |
281 | destruction. very bad things might happen otherwise (usually segfaults). |
972 | When Coro is compiled using the pthread backend (which isn't |
|
|
973 | recommended but required on many BSDs as their libcs are completely |
|
|
974 | broken), then coro will not survive a fork. There is no known |
|
|
975 | workaround except to fix your libc and use a saner backend. |
282 | |
976 | |
|
|
977 | perl process emulation ("threads") |
283 | - this module is not thread-safe. You should only ever use this module |
978 | This module is not perl-pseudo-thread-safe. You should only ever use |
284 | from the same thread (this requirement might be loosened in the future |
979 | this module from the first thread (this requirement might be removed |
285 | to allow per-thread schedulers, but Coro::State does not yet allow |
980 | in the future to allow per-thread schedulers, but Coro::State does |
286 | this). |
981 | not yet allow this). I recommend disabling thread support and using |
|
|
982 | processes, as having the windows process emulation enabled under |
|
|
983 | unix roughly halves perl performance, even when not used. |
|
|
984 | |
|
|
985 | Attempts to use threads created in another emulated process will |
|
|
986 | crash ("cleanly", with a null pointer exception). |
|
|
987 | |
|
|
988 | coro switching is not signal safe |
|
|
989 | You must not switch to another coro from within a signal handler |
|
|
990 | (only relevant with %SIG - most event libraries provide safe |
|
|
991 | signals), *unless* you are sure you are not interrupting a Coro |
|
|
992 | function. |
|
|
993 | |
|
|
994 | That means you *MUST NOT* call any function that might "block" the |
|
|
995 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
|
|
996 | anything that calls those. Everything else, including calling |
|
|
997 | "ready", works. |
|
|
998 | |
|
|
999 | WINDOWS PROCESS EMULATION |
|
|
1000 | A great many people seem to be confused about ithreads (for example, |
|
|
1001 | Chip Salzenberg called me unintelligent, incapable, stupid and gullible, |
|
|
1002 | while in the same mail making rather confused statements about perl |
|
|
1003 | ithreads (for example, that memory or files would be shared), showing |
|
|
1004 | his lack of understanding of this area - if it is hard to understand for |
|
|
1005 | Chip, it is probably not obvious to everybody). |
|
|
1006 | |
|
|
1007 | What follows is an ultra-condensed version of my talk about threads in |
|
|
1008 | scripting languages given on the perl workshop 2009: |
|
|
1009 | |
|
|
1010 | The so-called "ithreads" were originally implemented for two reasons: |
|
|
1011 | first, to (badly) emulate unix processes on native win32 perls, and |
|
|
1012 | secondly, to replace the older, real thread model ("5.005-threads"). |
|
|
1013 | |
|
|
1014 | It does that by using threads instead of OS processes. The difference |
|
|
1015 | between processes and threads is that threads share memory (and other |
|
|
1016 | state, such as files) between threads within a single process, while |
|
|
1017 | processes do not share anything (at least not semantically). That means |
|
|
1018 | that modifications done by one thread are seen by others, while |
|
|
1019 | modifications by one process are not seen by other processes. |
|
|
1020 | |
|
|
1021 | The "ithreads" work exactly like that: when creating a new ithreads |
|
|
1022 | process, all state is copied (memory is copied physically, files and |
|
|
1023 | code is copied logically). Afterwards, it isolates all modifications. On |
|
|
1024 | UNIX, the same behaviour can be achieved by using operating system |
|
|
1025 | processes, except that UNIX typically uses hardware built into the |
|
|
1026 | system to do this efficiently, while the windows process emulation |
|
|
1027 | emulates this hardware in software (rather efficiently, but of course it |
|
|
1028 | is still much slower than dedicated hardware). |
|
|
1029 | |
|
|
1030 | As mentioned before, loading code, modifying code, modifying data |
|
|
1031 | structures and so on is only visible in the ithreads process doing the |
|
|
1032 | modification, not in other ithread processes within the same OS process. |
|
|
1033 | |
|
|
1034 | This is why "ithreads" do not implement threads for perl at all, only |
|
|
1035 | processes. What makes it so bad is that on non-windows platforms, you |
|
|
1036 | can actually take advantage of custom hardware for this purpose (as |
|
|
1037 | evidenced by the forks module, which gives you the (i-) threads API, |
|
|
1038 | just much faster). |
|
|
1039 | |
|
|
1040 | Sharing data is in the i-threads model is done by transfering data |
|
|
1041 | structures between threads using copying semantics, which is very slow - |
|
|
1042 | shared data simply does not exist. Benchmarks using i-threads which are |
|
|
1043 | communication-intensive show extremely bad behaviour with i-threads (in |
|
|
1044 | fact, so bad that Coro, which cannot take direct advantage of multiple |
|
|
1045 | CPUs, is often orders of magnitude faster because it shares data using |
|
|
1046 | real threads, refer to my talk for details). |
|
|
1047 | |
|
|
1048 | As summary, i-threads *use* threads to implement processes, while the |
|
|
1049 | compatible forks module *uses* processes to emulate, uhm, processes. |
|
|
1050 | I-threads slow down every perl program when enabled, and outside of |
|
|
1051 | windows, serve no (or little) practical purpose, but disadvantages every |
|
|
1052 | single-threaded Perl program. |
|
|
1053 | |
|
|
1054 | This is the reason that I try to avoid the name "ithreads", as it is |
|
|
1055 | misleading as it implies that it implements some kind of thread model |
|
|
1056 | for perl, and prefer the name "windows process emulation", which |
|
|
1057 | describes the actual use and behaviour of it much better. |
287 | |
1058 | |
288 | SEE ALSO |
1059 | SEE ALSO |
|
|
1060 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
|
|
1061 | |
|
|
1062 | Debugging: Coro::Debug. |
|
|
1063 | |
289 | Support/Utility: Coro::Specific, Coro::State, Coro::Util. |
1064 | Support/Utility: Coro::Specific, Coro::Util. |
290 | |
1065 | |
291 | Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
1066 | Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
292 | Coro::SemaphoreSet, Coro::RWLock. |
1067 | Coro::SemaphoreSet, Coro::RWLock. |
293 | |
1068 | |
294 | Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket, |
1069 | I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO. |
|
|
1070 | |
|
|
1071 | Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP |
|
|
1072 | for a better-working alternative), Coro::BDB, Coro::Storable, |
295 | Coro::Select. |
1073 | Coro::Select. |
296 | |
1074 | |
297 | Embedding: <Coro:MakeMaker> |
1075 | XS API: Coro::MakeMaker. |
|
|
1076 | |
|
|
1077 | Low level Configuration, Thread Environment, Continuations: Coro::State. |
298 | |
1078 | |
299 | AUTHOR |
1079 | AUTHOR |
300 | Marc Lehmann <schmorp@schmorp.de> |
1080 | Marc Lehmann <schmorp@schmorp.de> |
301 | http://home.schmorp.de/ |
1081 | http://home.schmorp.de/ |
302 | |
1082 | |