… | |
… | |
40 | points in your program, so locking and parallel access are rarely an |
40 | points in your program, so locking and parallel access are rarely an |
41 | issue, making thread programming much safer and easier than using other |
41 | issue, making thread programming much safer and easier than using other |
42 | thread models. |
42 | thread models. |
43 | |
43 | |
44 | Unlike the so-called "Perl threads" (which are not actually real threads |
44 | Unlike the so-called "Perl threads" (which are not actually real threads |
45 | but only the windows process emulation (see section of same name for more |
45 | but only the windows process emulation (see section of same name for |
46 | details) ported to unix, and as such act as processes), Coro provides |
46 | more details) ported to UNIX, and as such act as processes), Coro |
47 | a full shared address space, which makes communication between threads |
47 | provides a full shared address space, which makes communication between |
48 | very easy. And Coro's threads are fast, too: disabling the Windows |
48 | threads very easy. And coro threads are fast, too: disabling the Windows |
49 | process emulation code in your perl and using Coro can easily result in |
49 | process emulation code in your perl and using Coro can easily result in |
50 | a two to four times speed increase for your programs. A parallel matrix |
50 | a two to four times speed increase for your programs. A parallel matrix |
51 | multiplication benchmark runs over 300 times faster on a single core than |
51 | multiplication benchmark (very communication-intensive) runs over 300 |
52 | perl's pseudo-threads on a quad core using all four cores. |
52 | times faster on a single core than perls pseudo-threads on a quad core |
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53 | using all four cores. |
53 | |
54 | |
54 | Coro achieves that by supporting multiple running interpreters that share |
55 | Coro achieves that by supporting multiple running interpreters that share |
55 | data, which is especially useful to code pseudo-parallel processes and |
56 | data, which is especially useful to code pseudo-parallel processes and |
56 | for event-based programming, such as multiple HTTP-GET requests running |
57 | for event-based programming, such as multiple HTTP-GET requests running |
57 | concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro |
58 | concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro |
… | |
… | |
63 | variables (see L<Coro::State> for more configuration and background info). |
64 | variables (see L<Coro::State> for more configuration and background info). |
64 | |
65 | |
65 | See also the C<SEE ALSO> section at the end of this document - the Coro |
66 | See also the C<SEE ALSO> section at the end of this document - the Coro |
66 | module family is quite large. |
67 | module family is quite large. |
67 | |
68 | |
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69 | =head1 CORO THREAD LIFE CYCLE |
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70 | |
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71 | During the long and exciting (or not) life of a coro thread, it goes |
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72 | through a number of states: |
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73 | |
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74 | =over 4 |
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75 | |
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76 | =item 1. Creation |
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77 | |
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78 | The first thing in the life of a coro thread is it's creation - |
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79 | obviously. The typical way to create a thread is to call the C<async |
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80 | BLOCK> function: |
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81 | |
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82 | async { |
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83 | # thread code goes here |
|
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84 | }; |
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85 | |
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86 | You can also pass arguments, which are put in C<@_>: |
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87 | |
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88 | async { |
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89 | print $_[1]; # prints 2 |
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90 | } 1, 2, 3; |
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91 | |
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92 | This creates a new coro thread and puts it into the ready queue, meaning |
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93 | it will run as soon as the CPU is free for it. |
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94 | |
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95 | C<async> will return a coro object - you can store this for future |
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96 | reference or ignore it, the thread itself will keep a reference to it's |
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97 | thread object - threads are alive on their own. |
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98 | |
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99 | Another way to create a thread is to call the C<new> constructor with a |
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100 | code-reference: |
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101 | |
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102 | new Coro sub { |
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103 | # thread code goes here |
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104 | }, @optional_arguments; |
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105 | |
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106 | This is quite similar to calling C<async>, but the important difference is |
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107 | that the new thread is not put into the ready queue, so the thread will |
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108 | not run until somebody puts it there. C<async> is, therefore, identical to |
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109 | this sequence: |
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110 | |
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111 | my $coro = new Coro sub { |
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112 | # thread code goes here |
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113 | }; |
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114 | $coro->ready; |
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115 | return $coro; |
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116 | |
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117 | =item 2. Startup |
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118 | |
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119 | When a new coro thread is created, only a copy of the code reference |
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120 | and the arguments are stored, no extra memory for stacks and so on is |
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121 | allocated, keeping the coro thread in a low-memory state. |
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122 | |
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123 | Only when it actually starts executing will all the resources be finally |
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124 | allocated. |
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125 | |
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126 | The optional arguments specified at coro creation are available in C<@_>, |
|
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127 | similar to function calls. |
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128 | |
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129 | =item 3. Running / Blocking |
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130 | |
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131 | A lot can happen after the coro thread has started running. Quite usually, |
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132 | it will not run to the end in one go (because you could use a function |
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133 | instead), but it will give up the CPU regularly because it waits for |
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134 | external events. |
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135 | |
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136 | As long as a coro thread runs, it's coro object is available in the global |
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137 | variable C<$Coro::current>. |
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138 | |
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139 | The low-level way to give up the CPU is to call the scheduler, which |
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140 | selects a new coro thread to run: |
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141 | |
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142 | Coro::schedule; |
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143 | |
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144 | Since running threads are not in the ready queue, calling the scheduler |
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145 | without doing anything else will block the coro thread forever - you need |
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146 | to arrange either for the coro to put woken up (readied) by some other |
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147 | event or some other thread, or you can put it into the ready queue before |
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148 | scheduling: |
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149 | |
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150 | # this is exactly what Coro::cede does |
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151 | $Coro::current->ready; |
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152 | Coro::schedule; |
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153 | |
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154 | All the higher-level synchronisation methods (Coro::Semaphore, |
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155 | Coro::rouse_*...) are actually implemented via C<< ->ready >> and C<< |
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156 | Coro::schedule >>. |
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157 | |
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158 | While the coro thread is running it also might get assigned a C-level |
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159 | thread, or the C-level thread might be unassigned from it, as the Coro |
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160 | runtime wishes. A C-level thread needs to be assigned when your perl |
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161 | thread calls into some C-level function and that function in turn calls |
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162 | perl and perl then wants to switch coroutines. This happens most often |
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163 | when you run an event loop and block in the callback, or when perl |
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164 | itself calls some function such as C<AUTOLOAD> or methods via the C<tie> |
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165 | mechanism. |
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166 | |
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167 | =item 4. Termination |
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168 | |
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169 | Many threads actually terminate after some time. There are a number of |
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170 | ways to terminate a coro thread, the simplest is returning from the |
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171 | top-level code reference: |
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172 | |
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173 | async { |
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174 | # after returning from here, the coro thread is terminated |
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175 | }; |
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176 | |
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177 | async { |
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178 | return if 0.5 < rand; # terminate a little earlier, maybe |
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179 | print "got a chance to print this\n"; |
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180 | # or here |
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181 | }; |
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182 | |
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183 | Any values returned from the coroutine can be recovered using C<< ->join |
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184 | >>: |
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185 | |
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186 | my $coro = async { |
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187 | "hello, world\n" # return a string |
|
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188 | }; |
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189 | |
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190 | my $hello_world = $coro->join; |
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191 | |
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192 | print $hello_world; |
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193 | |
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194 | Another way to terminate is to call C<< Coro::terminate >>, which at any |
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195 | subroutine call nesting level: |
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196 | |
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197 | async { |
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198 | Coro::terminate "return value 1", "return value 2"; |
|
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199 | }; |
|
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200 | |
|
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201 | And yet another way is to C<< ->cancel >> the coro thread from another |
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202 | thread: |
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203 | |
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204 | my $coro = async { |
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205 | exit 1; |
|
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206 | }; |
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207 | |
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208 | $coro->cancel; # an also accept values for ->join to retrieve |
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209 | |
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210 | Cancellation I<can> be dangerous - it's a bit like calling C<exit> without |
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211 | actually exiting, and might leave C libraries and XS modules in a weird |
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212 | state. Unlike other thread implementations, however, Coro is exceptionally |
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213 | safe with regards to cancellation, as perl will always be in a consistent |
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214 | state. |
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215 | |
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216 | So, cancelling a thread that runs in an XS event loop might not be the |
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217 | best idea, but any other combination that deals with perl only (cancelling |
|
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218 | when a thread is in a C<tie> method or an C<AUTOLOAD> for example) is |
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219 | safe. |
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220 | |
|
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221 | =item 5. Cleanup |
|
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222 | |
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223 | Threads will allocate various resources. Most but not all will be returned |
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224 | when a thread terminates, during clean-up. |
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225 | |
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226 | Cleanup is quite similar to throwing an uncaught exception: perl will |
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227 | work it's way up through all subroutine calls and blocks. On it's way, it |
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228 | will release all C<my> variables, undo all C<local>'s and free any other |
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229 | resources truly local to the thread. |
|
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230 | |
|
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231 | So, a common way to free resources is to keep them referenced only by my |
|
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232 | variables: |
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233 | |
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234 | async { |
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235 | my $big_cache = new Cache ...; |
|
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236 | }; |
|
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237 | |
|
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238 | If there are no other references, then the C<$big_cache> object will be |
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239 | freed when the thread terminates, regardless of how it does so. |
|
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240 | |
|
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241 | What it does C<NOT> do is unlock any Coro::Semaphores or similar |
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242 | resources, but that's where the C<guard> methods come in handy: |
|
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243 | |
|
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244 | my $sem = new Coro::Semaphore; |
|
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245 | |
|
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246 | async { |
|
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247 | my $lock_guard = $sem->guard; |
|
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248 | # if we reutrn, or die or get cancelled, here, |
|
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249 | # then the semaphore will be "up"ed. |
|
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250 | }; |
|
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251 | |
|
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252 | The C<Guard::guard> function comes in handy for any custom cleanup you |
|
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253 | might want to do: |
|
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254 | |
|
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255 | async { |
|
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256 | my $window = new Gtk2::Window "toplevel"; |
|
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257 | # The window will not be cleaned up automatically, even when $window |
|
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258 | # gets freed, so use a guard to ensure it's destruction |
|
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259 | # in case of an error: |
|
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260 | my $window_guard = Guard::guard { $window->destroy }; |
|
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261 | |
|
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262 | # we are safe here |
|
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263 | }; |
|
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264 | |
|
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265 | Last not least, C<local> can often be handy, too, e.g. when temporarily |
|
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266 | replacing the coro thread description: |
|
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267 | |
|
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268 | sub myfunction { |
|
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269 | local $Coro::current->{desc} = "inside myfunction(@_)"; |
|
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270 | |
|
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271 | # if we return or die here, the description will be restored |
|
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272 | } |
|
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273 | |
|
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274 | =item 6. Viva La Zombie Muerte |
|
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275 | |
|
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276 | Even after a thread has terminated and cleaned up it's resources, the coro |
|
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277 | object still is there and stores the return values of the thread. Only in |
|
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278 | this state will the coro object be "reference counted" in the normal perl |
|
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279 | sense: the thread code keeps a reference to it when it is active, but not |
|
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280 | after it has terminated. |
|
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281 | |
|
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282 | The means the coro object gets freed automatically when the thread has |
|
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283 | terminated and cleaned up and there arenot other references. |
|
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284 | |
|
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285 | If there are, the coro object will stay around, and you can call C<< |
|
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286 | ->join >> as many times as you wish to retrieve the result values: |
|
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287 | |
|
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288 | async { |
|
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289 | print "hi\n"; |
|
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290 | 1 |
|
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291 | }; |
|
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292 | |
|
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293 | # run the async above, and free everything before returning |
|
|
294 | # from Coro::cede: |
|
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295 | Coro::cede; |
|
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296 | |
|
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297 | { |
|
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298 | my $coro = async { |
|
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299 | print "hi\n"; |
|
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300 | 1 |
|
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301 | }; |
|
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302 | |
|
|
303 | # run the async above, and clean up, but do not free the coro |
|
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304 | # object: |
|
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305 | Coro::cede; |
|
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306 | |
|
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307 | # optionally retrieve the result values |
|
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308 | my @results = $coro->join; |
|
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309 | |
|
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310 | # now $coro goes out of scope, and presumably gets freed |
|
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311 | }; |
|
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312 | |
|
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313 | =back |
|
|
314 | |
68 | =cut |
315 | =cut |
69 | |
316 | |
70 | package Coro; |
317 | package Coro; |
71 | |
318 | |
72 | use common::sense; |
319 | use common::sense; |
… | |
… | |
81 | |
328 | |
82 | our $idle; # idle handler |
329 | our $idle; # idle handler |
83 | our $main; # main coro |
330 | our $main; # main coro |
84 | our $current; # current coro |
331 | our $current; # current coro |
85 | |
332 | |
86 | our $VERSION = 5.26; |
333 | our $VERSION = 5.371; |
87 | |
334 | |
88 | our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait); |
335 | our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub rouse_cb rouse_wait); |
89 | our %EXPORT_TAGS = ( |
336 | our %EXPORT_TAGS = ( |
90 | prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], |
337 | prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)], |
91 | ); |
338 | ); |