1 | NAME |
1 | NAME |
2 | Coro - the only real threads in perl |
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 |
9 | print "2\n"; |
9 | print "2\n"; |
10 | cede; # yield back to main |
10 | cede; # yield back to main |
11 | print "4\n"; |
11 | print "4\n"; |
12 | }; |
12 | }; |
13 | print "1\n"; |
13 | print "1\n"; |
14 | cede; # yield to coro |
14 | cede; # yield to coro |
15 | print "3\n"; |
15 | print "3\n"; |
16 | cede; # and again |
16 | cede; # and again |
17 | |
17 | |
18 | # use locking |
18 | # use locking |
19 | use Coro::Semaphore; |
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20 | my $lock = new Coro::Semaphore; |
19 | my $lock = new Coro::Semaphore; |
21 | my $locked; |
20 | my $locked; |
22 | |
21 | |
23 | $lock->down; |
22 | $lock->down; |
24 | $locked = 1; |
23 | $locked = 1; |
25 | $lock->up; |
24 | $lock->up; |
26 | |
25 | |
27 | DESCRIPTION |
26 | DESCRIPTION |
28 | For a tutorial-style introduction, please read the Coro::Intro manpage. |
27 | For a tutorial-style introduction, please read the Coro::Intro manpage. |
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37 | easily-identified points in your program, so locking and parallel access |
36 | easily-identified points in your program, so locking and parallel access |
38 | are rarely an issue, making thread programming much safer and easier |
37 | are rarely an issue, making thread programming much safer and easier |
39 | than using other thread models. |
38 | than using other thread models. |
40 | |
39 | |
41 | Unlike the so-called "Perl threads" (which are not actually real threads |
40 | Unlike the so-called "Perl threads" (which are not actually real threads |
42 | but only the windows process emulation ported to unix, and as such act |
41 | but only the windows process emulation (see section of same name for |
43 | as processes), Coro provides a full shared address space, which makes |
42 | more details) ported to UNIX, and as such act as processes), Coro |
44 | communication between threads very easy. And Coro's threads are fast, |
43 | provides a full shared address space, which makes communication between |
45 | too: disabling the Windows process emulation code in your perl and using |
44 | threads very easy. And coro threads are fast, too: disabling the Windows |
46 | Coro can easily result in a two to four times speed increase for your |
45 | process emulation code in your perl and using Coro can easily result in |
47 | programs. A parallel matrix multiplication benchmark runs over 300 times |
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 |
48 | faster on a single core than perl's pseudo-threads on a quad core using |
48 | times faster on a single core than perls pseudo-threads on a quad core |
49 | all four cores. |
49 | using all four cores. |
50 | |
50 | |
51 | Coro achieves that by supporting multiple running interpreters that |
51 | Coro achieves that by supporting multiple running interpreters that |
52 | share data, which is especially useful to code pseudo-parallel processes |
52 | share data, which is especially useful to code pseudo-parallel processes |
53 | and for event-based programming, such as multiple HTTP-GET requests |
53 | and for event-based programming, such as multiple HTTP-GET requests |
54 | running concurrently. See Coro::AnyEvent to learn more on how to |
54 | running concurrently. See Coro::AnyEvent to learn more on how to |
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61 | background info). |
61 | background info). |
62 | |
62 | |
63 | See also the "SEE ALSO" section at the end of this document - the Coro |
63 | See also the "SEE ALSO" section at the end of this document - the Coro |
64 | module family is quite large. |
64 | module family is quite large. |
65 | |
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 | |
66 | GLOBAL VARIABLES |
342 | GLOBAL VARIABLES |
67 | $Coro::main |
343 | $Coro::main |
68 | This variable stores the Coro object that represents the main |
344 | This variable stores the Coro object that represents the main |
69 | program. While you cna "ready" it and do most other things you can |
345 | program. While you can "ready" it and do most other things you can |
70 | do to coro, it is mainly useful to compare again $Coro::current, to |
346 | do to coro, it is mainly useful to compare again $Coro::current, to |
71 | see whether you are running in the main program or not. |
347 | see whether you are running in the main program or not. |
72 | |
348 | |
73 | $Coro::current |
349 | $Coro::current |
74 | The Coro object representing the current coro (the last coro that |
350 | The Coro object representing the current coro (the last coro that |
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82 | $Coro::idle |
358 | $Coro::idle |
83 | This variable is mainly useful to integrate Coro into event loops. |
359 | This variable is mainly useful to integrate Coro into event loops. |
84 | It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
360 | It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
85 | is pretty low-level functionality. |
361 | is pretty low-level functionality. |
86 | |
362 | |
87 | This variable stores either a Coro object or a callback. |
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). |
88 | |
366 | |
89 | If it is a callback, the it is called whenever the scheduler finds |
367 | The default implementation dies with "FATAL: deadlock detected.", |
90 | no ready coros to run. The default implementation prints "FATAL: |
368 | followed by a thread listing, because the program has no other way |
91 | deadlock detected" and exits, because the program has no other way |
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92 | to continue. |
369 | to continue. |
93 | |
370 | |
94 | If it is a coro object, then this object will be readied (without |
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95 | invoking any ready hooks, however) when the scheduler finds no other |
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96 | ready coros to run. |
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97 | |
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98 | This hook is overwritten by modules such as "Coro::EV" and |
371 | This hook is overwritten by modules such as "Coro::EV" and |
99 | "Coro::AnyEvent" to wait on an external event that hopefully wake up |
372 | "Coro::AnyEvent" to wait on an external event that hopefully wakes |
100 | a coro so the scheduler can run it. |
373 | up a coro so the scheduler can run it. |
101 | |
374 | |
102 | Note that the callback *must not*, under any circumstances, block |
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103 | the current coro. Normally, this is achieved by having an "idle |
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104 | coro" that calls the event loop and then blocks again, and then |
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105 | readying that coro in the idle handler, or by simply placing the |
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106 | idle coro in this variable. |
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107 | |
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108 | See Coro::Event or Coro::AnyEvent for examples of using this |
375 | See Coro::EV or Coro::AnyEvent for examples of using this technique. |
109 | technique. |
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110 | |
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111 | Please note that if your callback recursively invokes perl (e.g. for |
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112 | event handlers), then it must be prepared to be called recursively |
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113 | itself. |
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114 | |
376 | |
115 | SIMPLE CORO CREATION |
377 | SIMPLE CORO CREATION |
116 | async { ... } [@args...] |
378 | async { ... } [@args...] |
117 | Create a new coro and return its Coro object (usually unused). The |
379 | Create a new coro and return its Coro object (usually unused). The |
118 | coro will be put into the ready queue, so it will start running |
380 | coro will be put into the ready queue, so it will start running |
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181 | |
443 | |
182 | schedule |
444 | schedule |
183 | Calls the scheduler. The scheduler will find the next coro that is |
445 | Calls the scheduler. The scheduler will find the next coro that is |
184 | to be run from the ready queue and switches to it. The next coro to |
446 | to be run from the ready queue and switches to it. The next coro to |
185 | be run is simply the one with the highest priority that is longest |
447 | be run is simply the one with the highest priority that is longest |
186 | in its ready queue. If there is no coro ready, it will clal the |
448 | in its ready queue. If there is no coro ready, it will call the |
187 | $Coro::idle hook. |
449 | $Coro::idle hook. |
188 | |
450 | |
189 | Please note that the current coro will *not* be put into the ready |
451 | Please note that the current coro will *not* be put into the ready |
190 | queue, so calling this function usually means you will never be |
452 | queue, so calling this function usually means you will never be |
191 | called again unless something else (e.g. an event handler) calls |
453 | called again unless something else (e.g. an event handler) calls |
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216 | *any* coro, regardless of priority. This is useful sometimes to |
478 | *any* coro, regardless of priority. This is useful sometimes to |
217 | ensure progress is made. |
479 | ensure progress is made. |
218 | |
480 | |
219 | terminate [arg...] |
481 | terminate [arg...] |
220 | Terminates the current coro with the given status values (see |
482 | Terminates the current coro with the given status values (see |
221 | cancel). |
483 | cancel). The values will not be copied, but referenced directly. |
222 | |
484 | |
223 | Coro::on_enter BLOCK, Coro::on_leave BLOCK |
485 | Coro::on_enter BLOCK, Coro::on_leave BLOCK |
224 | These function install enter and leave winders in the current scope. |
486 | These function install enter and leave winders in the current scope. |
225 | The enter block will be executed when on_enter is called and |
487 | The enter block will be executed when on_enter is called and |
226 | whenever the current coro is re-entered by the scheduler, while the |
488 | whenever the current coro is re-entered by the scheduler, while the |
… | |
… | |
238 | |
500 | |
239 | These functions implement the same concept as "dynamic-wind" in |
501 | These functions implement the same concept as "dynamic-wind" in |
240 | scheme does, and are useful when you want to localise some resource |
502 | scheme does, and are useful when you want to localise some resource |
241 | to a specific coro. |
503 | to a specific coro. |
242 | |
504 | |
243 | They slow down coro switching considerably for coros that use them |
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 |
244 | (But coro switching is still reasonably fast if the handlers are |
507 | is still reasonably fast if the handlers are fast). |
245 | fast). |
|
|
246 | |
508 | |
247 | These functions are best understood by an example: The following |
509 | These functions are best understood by an example: The following |
248 | function will change the current timezone to |
510 | function will change the current timezone to |
249 | "Antarctica/South_Pole", which requires a call to "tzset", but by |
511 | "Antarctica/South_Pole", which requires a call to "tzset", but by |
250 | using "on_enter" and "on_leave", which remember/change the current |
512 | using "on_enter" and "on_leave", which remember/change the current |
… | |
… | |
274 | |
536 | |
275 | This can be used to localise about any resource (locale, uid, |
537 | This can be used to localise about any resource (locale, uid, |
276 | current working directory etc.) to a block, despite the existance of |
538 | current working directory etc.) to a block, despite the existance of |
277 | other coros. |
539 | other coros. |
278 | |
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}; |
|
|
561 | } |
|
|
562 | |
|
|
563 | # use like this: |
|
|
564 | timeslice { |
|
|
565 | # The following is an endless loop that would normally |
|
|
566 | # monopolise the process. Since it runs in a timesliced |
|
|
567 | # environment, it will regularly cede to other threads. |
|
|
568 | while () { } |
|
|
569 | }; |
|
|
570 | |
279 | killall |
571 | killall |
280 | Kills/terminates/cancels all coros except the currently running one. |
572 | Kills/terminates/cancels all coros except the currently running one. |
281 | |
573 | |
282 | Note that while this will try to free some of the main interpreter |
574 | Note that while this will try to free some of the main interpreter |
283 | resources if the calling coro isn't the main coro, but one cannot |
575 | resources if the calling coro isn't the main coro, but one cannot |
… | |
… | |
328 | To avoid this, it is best to put a suspended coro into the ready |
620 | To avoid this, it is best to put a suspended coro into the ready |
329 | queue unconditionally, as every synchronisation mechanism must |
621 | queue unconditionally, as every synchronisation mechanism must |
330 | protect itself against spurious wakeups, and the one in the Coro |
622 | protect itself against spurious wakeups, and the one in the Coro |
331 | family certainly do that. |
623 | family certainly do that. |
332 | |
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 | |
333 | $is_ready = $coro->is_ready |
641 | $is_ready = $coro->is_ready |
334 | Returns true iff the Coro object is in the ready queue. Unless the |
642 | Returns true iff the Coro object is in the ready queue. Unless the |
335 | Coro object gets destroyed, it will eventually be scheduled by the |
643 | Coro object gets destroyed, it will eventually be scheduled by the |
336 | scheduler. |
644 | scheduler. |
337 | |
645 | |
… | |
… | |
343 | $is_suspended = $coro->is_suspended |
651 | $is_suspended = $coro->is_suspended |
344 | Returns true iff this Coro object has been suspended. Suspended |
652 | Returns true iff this Coro object has been suspended. Suspended |
345 | Coros will not ever be scheduled. |
653 | Coros will not ever be scheduled. |
346 | |
654 | |
347 | $coro->cancel (arg...) |
655 | $coro->cancel (arg...) |
348 | Terminates the given Coro and makes it return the given arguments as |
656 | Terminates the given Coro thread and makes it return the given |
349 | status (default: the empty list). Never returns if the Coro is the |
657 | arguments as status (default: an empty list). Never returns if the |
350 | current Coro. |
658 | Coro is the current Coro. |
|
|
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. |
351 | |
733 | |
352 | $coro->schedule_to |
734 | $coro->schedule_to |
353 | Puts the current coro to sleep (like "Coro::schedule"), but instead |
735 | Puts the current coro to sleep (like "Coro::schedule"), but instead |
354 | of continuing with the next coro from the ready queue, always switch |
736 | of continuing with the next coro from the ready queue, always switch |
355 | to the given coro object (regardless of priority etc.). The |
737 | to the given coro object (regardless of priority etc.). The |
… | |
… | |
372 | Otherwise clears the exception object. |
754 | Otherwise clears the exception object. |
373 | |
755 | |
374 | Coro will check for the exception each time a schedule-like-function |
756 | Coro will check for the exception each time a schedule-like-function |
375 | returns, i.e. after each "schedule", "cede", |
757 | returns, i.e. after each "schedule", "cede", |
376 | "Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of |
758 | "Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of |
377 | these functions detect this case and return early in case an |
759 | those functions (all that are part of Coro itself) detect this case |
378 | exception is pending. |
760 | and return early in case an exception is pending. |
379 | |
761 | |
380 | The exception object will be thrown "as is" with the specified |
762 | The exception object will be thrown "as is" with the specified |
381 | scalar in $@, i.e. if it is a string, no line number or newline will |
763 | scalar in $@, i.e. if it is a string, no line number or newline will |
382 | be appended (unlike with "die"). |
764 | be appended (unlike with "die"). |
383 | |
765 | |
384 | This can be used as a softer means than "cancel" to ask a coro to |
766 | This can be used as a softer means than either "cancel" or |
385 | end itself, although there is no guarantee that the exception will |
767 | "safe_cancel "to ask a coro to end itself, although there is no |
386 | lead to termination, and if the exception isn't caught it might well |
768 | guarantee that the exception will lead to termination, and if the |
387 | end the whole program. |
769 | exception isn't caught it might well end the whole program. |
388 | |
770 | |
389 | You might also think of "throw" as being the moral equivalent of |
771 | You might also think of "throw" as being the moral equivalent of |
390 | "kill"ing a coro with a signal (in this case, a scalar). |
772 | "kill"ing a coro with a signal (in this case, a scalar). |
391 | |
773 | |
392 | $coro->join |
774 | $coro->join |
393 | Wait until the coro terminates and return any values given to the |
775 | Wait until the coro terminates and return any values given to the |
394 | "terminate" or "cancel" functions. "join" can be called concurrently |
776 | "terminate" or "cancel" functions. "join" can be called concurrently |
395 | from multiple coro, and all will be resumed and given the status |
777 | from multiple threads, and all will be resumed and given the status |
396 | return once the $coro terminates. |
778 | return once the $coro terminates. |
397 | |
779 | |
398 | $coro->on_destroy (\&cb) |
780 | $coro->on_destroy (\&cb) |
399 | Registers a callback that is called when this coro gets destroyed, |
781 | Registers a callback that is called when this coro thread gets |
|
|
782 | destroyed, that is, after it's resources have been freed but before |
400 | but before it is joined. The callback gets passed the terminate |
783 | it is joined. The callback gets passed the terminate/cancel |
401 | arguments, if any, and *must not* die, under any circumstances. |
784 | arguments, if any, and *must not* die, under any circumstances. |
402 | |
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 | |
403 | $oldprio = $coro->prio ($newprio) |
789 | $oldprio = $coro->prio ($newprio) |
404 | Sets (or gets, if the argument is missing) the priority of the coro. |
790 | Sets (or gets, if the argument is missing) the priority of the coro |
405 | Higher priority coro get run before lower priority coro. Priorities |
791 | thread. Higher priority coro get run before lower priority coros. |
406 | are small signed integers (currently -4 .. +3), that you can refer |
792 | Priorities are small signed integers (currently -4 .. +3), that you |
407 | to using PRIO_xxx constants (use the import tag :prio to get then): |
793 | can refer to using PRIO_xxx constants (use the import tag :prio to |
|
|
794 | get then): |
408 | |
795 | |
409 | 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 |
410 | 3 > 1 > 0 > -1 > -3 > -4 |
797 | 3 > 1 > 0 > -1 > -3 > -4 |
411 | |
798 | |
412 | # set priority to HIGH |
799 | # set priority to HIGH |
413 | current->prio (PRIO_HIGH); |
800 | current->prio (PRIO_HIGH); |
414 | |
801 | |
415 | The idle coro ($Coro::idle) always has a lower priority than any |
802 | The idle coro thread ($Coro::idle) always has a lower priority than |
416 | existing coro. |
803 | any existing coro. |
417 | |
804 | |
418 | Changing the priority of the current coro will take effect |
805 | Changing the priority of the current coro will take effect |
419 | immediately, but changing the priority of coro in the ready queue |
806 | immediately, but changing the priority of a coro in the ready queue |
420 | (but not running) will only take effect after the next schedule (of |
807 | (but not running) will only take effect after the next schedule (of |
421 | that coro). This is a bug that will be fixed in some future version. |
808 | that coro). This is a bug that will be fixed in some future version. |
422 | |
809 | |
423 | $newprio = $coro->nice ($change) |
810 | $newprio = $coro->nice ($change) |
424 | Similar to "prio", but subtract the given value from the priority |
811 | Similar to "prio", but subtract the given value from the priority |
425 | (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). |
426 | |
814 | |
427 | $olddesc = $coro->desc ($newdesc) |
815 | $olddesc = $coro->desc ($newdesc) |
428 | 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 |
429 | this coro. This is just a free-form string you can associate with a |
817 | this coro thread. This is just a free-form string you can associate |
430 | coro. |
818 | with a coro. |
431 | |
819 | |
432 | This method simply sets the "$coro->{desc}" member to the given |
820 | This method simply sets the "$coro->{desc}" member to the given |
433 | 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: |
|
|
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 | $Coro::current->{desc} = "my_long_function: phase 2"; |
|
|
831 | ... |
|
|
832 | } |
434 | |
833 | |
435 | GLOBAL FUNCTIONS |
834 | GLOBAL FUNCTIONS |
436 | Coro::nready |
835 | Coro::nready |
437 | Returns the number of coro that are currently in the ready state, |
836 | Returns the number of coro that are currently in the ready state, |
438 | i.e. that can be switched to by calling "schedule" directory or |
837 | i.e. that can be switched to by calling "schedule" directory or |
… | |
… | |
455 | The reason this function exists is that many event libraries (such |
854 | The reason this function exists is that many event libraries (such |
456 | as the venerable Event module) are not thread-safe (a weaker form of |
855 | as the venerable Event module) are not thread-safe (a weaker form of |
457 | reentrancy). This means you must not block within event callbacks, |
856 | reentrancy). This means you must not block within event callbacks, |
458 | otherwise you might suffer from crashes or worse. The only event |
857 | otherwise you might suffer from crashes or worse. The only event |
459 | library currently known that is safe to use without "unblock_sub" is |
858 | library currently known that is safe to use without "unblock_sub" is |
460 | EV. |
859 | EV (but you might still run into deadlocks if all event loops are |
|
|
860 | blocked). |
|
|
861 | |
|
|
862 | Coro will try to catch you when you block in the event loop |
|
|
863 | ("FATAL:$Coro::IDLE blocked itself"), but this is just best effort |
|
|
864 | and only works when you do not run your own event loop. |
461 | |
865 | |
462 | This function allows your callbacks to block by executing them in |
866 | This function allows your callbacks to block by executing them in |
463 | another coro where it is safe to block. One example where blocking |
867 | another coro where it is safe to block. One example where blocking |
464 | is handy is when you use the Coro::AIO functions to save results to |
868 | is handy is when you use the Coro::AIO functions to save results to |
465 | disk, for example. |
869 | disk, for example. |
… | |
… | |
476 | when you use a module that uses AnyEvent (and you use |
880 | when you use a module that uses AnyEvent (and you use |
477 | Coro::AnyEvent) and it provides callbacks that are the result of |
881 | Coro::AnyEvent) and it provides callbacks that are the result of |
478 | some event callback, then you must not block either, or use |
882 | some event callback, then you must not block either, or use |
479 | "unblock_sub". |
883 | "unblock_sub". |
480 | |
884 | |
481 | $cb = Coro::rouse_cb |
885 | $cb = rouse_cb |
482 | Create and return a "rouse callback". That's a code reference that, |
886 | Create and return a "rouse callback". That's a code reference that, |
483 | when called, will remember a copy of its arguments and notify the |
887 | when called, will remember a copy of its arguments and notify the |
484 | owner coro of the callback. |
888 | owner coro of the callback. |
485 | |
889 | |
486 | See the next function. |
890 | See the next function. |
487 | |
891 | |
488 | @args = Coro::rouse_wait [$cb] |
892 | @args = rouse_wait [$cb] |
489 | Wait for the specified rouse callback (or the last one that was |
893 | Wait for the specified rouse callback (or the last one that was |
490 | created in this coro). |
894 | created in this coro). |
491 | |
895 | |
492 | As soon as the callback is invoked (or when the callback was invoked |
896 | As soon as the callback is invoked (or when the callback was invoked |
493 | before "rouse_wait"), it will return the arguments originally passed |
897 | before "rouse_wait"), it will return the arguments originally passed |
494 | to the rouse callback. |
898 | to the rouse callback. In scalar context, that means you get the |
|
|
899 | *last* argument, just as if "rouse_wait" had a "return ($a1, $a2, |
|
|
900 | $a3...)" statement at the end. |
495 | |
901 | |
496 | See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
902 | See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
497 | example. |
903 | example. |
498 | |
904 | |
499 | HOW TO WAIT FOR A CALLBACK |
905 | HOW TO WAIT FOR A CALLBACK |
… | |
… | |
513 | But from within a coro, you often just want to write this: |
919 | But from within a coro, you often just want to write this: |
514 | |
920 | |
515 | my $status = wait_for_child $pid; |
921 | my $status = wait_for_child $pid; |
516 | |
922 | |
517 | Coro offers two functions specifically designed to make this easy, |
923 | Coro offers two functions specifically designed to make this easy, |
518 | "Coro::rouse_cb" and "Coro::rouse_wait". |
924 | "rouse_cb" and "rouse_wait". |
519 | |
925 | |
520 | The first function, "rouse_cb", generates and returns a callback that, |
926 | The first function, "rouse_cb", generates and returns a callback that, |
521 | when invoked, will save its arguments and notify the coro that created |
927 | when invoked, will save its arguments and notify the coro that created |
522 | the callback. |
928 | the callback. |
523 | |
929 | |
… | |
… | |
529 | function mentioned above: |
935 | function mentioned above: |
530 | |
936 | |
531 | sub wait_for_child($) { |
937 | sub wait_for_child($) { |
532 | my ($pid) = @_; |
938 | my ($pid) = @_; |
533 | |
939 | |
534 | my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb); |
940 | my $watcher = AnyEvent->child (pid => $pid, cb => rouse_cb); |
535 | |
941 | |
536 | my ($rpid, $rstatus) = Coro::rouse_wait; |
942 | my ($rpid, $rstatus) = rouse_wait; |
537 | $rstatus |
943 | $rstatus |
538 | } |
944 | } |
539 | |
945 | |
540 | In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
946 | In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
541 | you can roll your own, using "schedule": |
947 | you can roll your own, using "schedule" and "ready": |
542 | |
948 | |
543 | sub wait_for_child($) { |
949 | sub wait_for_child($) { |
544 | my ($pid) = @_; |
950 | my ($pid) = @_; |
545 | |
951 | |
546 | # store the current coro in $current, |
952 | # store the current coro in $current, |
… | |
… | |
549 | my ($done, $rstatus); |
955 | my ($done, $rstatus); |
550 | |
956 | |
551 | # pass a closure to ->child |
957 | # pass a closure to ->child |
552 | my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
958 | my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
553 | $rstatus = $_[1]; # remember rstatus |
959 | $rstatus = $_[1]; # remember rstatus |
554 | $done = 1; # mark $rstatus as valud |
960 | $done = 1; # mark $rstatus as valid |
|
|
961 | $current->ready; # wake up the waiting thread |
555 | }); |
962 | }); |
556 | |
963 | |
557 | # wait until the closure has been called |
964 | # wait until the closure has been called |
558 | schedule while !$done; |
965 | schedule while !$done; |
559 | |
966 | |
… | |
… | |
573 | in the future to allow per-thread schedulers, but Coro::State does |
980 | in the future to allow per-thread schedulers, but Coro::State does |
574 | not yet allow this). I recommend disabling thread support and using |
981 | not yet allow this). I recommend disabling thread support and using |
575 | processes, as having the windows process emulation enabled under |
982 | processes, as having the windows process emulation enabled under |
576 | unix roughly halves perl performance, even when not used. |
983 | unix roughly halves perl performance, even when not used. |
577 | |
984 | |
|
|
985 | Attempts to use threads created in another emulated process will |
|
|
986 | crash ("cleanly", with a null pointer exception). |
|
|
987 | |
578 | coro switching is not signal safe |
988 | coro switching is not signal safe |
579 | You must not switch to another coro from within a signal handler |
989 | You must not switch to another coro from within a signal handler |
580 | (only relevant with %SIG - most event libraries provide safe |
990 | (only relevant with %SIG - most event libraries provide safe |
581 | signals). |
991 | signals), *unless* you are sure you are not interrupting a Coro |
|
|
992 | function. |
582 | |
993 | |
583 | That means you *MUST NOT* call any function that might "block" the |
994 | That means you *MUST NOT* call any function that might "block" the |
584 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
995 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
585 | anything that calls those. Everything else, including calling |
996 | anything that calls those. Everything else, including calling |
586 | "ready", works. |
997 | "ready", works. |
587 | |
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. |
|
|
1058 | |
588 | SEE ALSO |
1059 | SEE ALSO |
589 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
1060 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
590 | |
1061 | |
591 | Debugging: Coro::Debug. |
1062 | Debugging: Coro::Debug. |
592 | |
1063 | |