… | |
… | |
3 | AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
3 | AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use AnyEvent::Fork; |
7 | use AnyEvent::Fork; |
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8 | |
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9 | AnyEvent::Fork |
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10 | ->new |
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11 | ->require ("MyModule") |
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12 | ->run ("MyModule::server", my $cv = AE::cv); |
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13 | |
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14 | my $fh = $cv->recv; |
8 | |
15 | |
9 | =head1 DESCRIPTION |
16 | =head1 DESCRIPTION |
10 | |
17 | |
11 | This module allows you to create new processes, without actually forking |
18 | This module allows you to create new processes, without actually forking |
12 | them from your current process (avoiding the problems of forking), but |
19 | them from your current process (avoiding the problems of forking), but |
13 | preserving most of the advantages of fork. |
20 | preserving most of the advantages of fork. |
14 | |
21 | |
15 | It can be used to create new worker processes or new independent |
22 | It can be used to create new worker processes or new independent |
16 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
23 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
17 | in pre-forked servers) but also to spawn new external processes (such as |
24 | in pre-forked servers) but also to spawn new external processes (such as |
18 | CGI scripts from a webserver), which can be faster (and more well behaved) |
25 | CGI scripts from a web server), which can be faster (and more well behaved) |
19 | than using fork+exec in big processes. |
26 | than using fork+exec in big processes. |
20 | |
27 | |
21 | Special care has been taken to make this module useful from other modules, |
28 | Special care has been taken to make this module useful from other modules, |
22 | while still supporting specialised environments such as L<App::Staticperl> |
29 | while still supporting specialised environments such as L<App::Staticperl> |
23 | or L<PAR::Packer>. |
30 | or L<PAR::Packer>. |
24 | |
31 | |
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32 | =head1 WHAT THIS MODULE IS NOT |
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33 | |
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34 | This module only creates processes and lets you pass file handles and |
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35 | strings to it, and run perl code. It does not implement any kind of RPC - |
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36 | there is no back channel from the process back to you, and there is no RPC |
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37 | or message passing going on. |
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38 | |
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39 | If you need some form of RPC, you can either implement it yourself |
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40 | in whatever way you like, use some message-passing module such |
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41 | as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use |
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42 | L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages, |
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43 | and so on. |
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44 | |
25 | =head1 PROBLEM STATEMENT |
45 | =head1 PROBLEM STATEMENT |
26 | |
46 | |
27 | There are two ways to implement parallel processing on UNIX like operating |
47 | There are two traditional ways to implement parallel processing on UNIX |
28 | systems - fork and process, and fork+exec and process. They have different |
48 | like operating systems - fork and process, and fork+exec and process. They |
29 | advantages and disadvantages that I describe below, together with how this |
49 | have different advantages and disadvantages that I describe below, |
30 | module tries to mitigate the disadvantages. |
50 | together with how this module tries to mitigate the disadvantages. |
31 | |
51 | |
32 | =over 4 |
52 | =over 4 |
33 | |
53 | |
34 | =item Forking from a big process can be very slow (a 5GB process needs |
54 | =item Forking from a big process can be very slow. |
35 | 0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead |
55 | |
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56 | A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This |
36 | is often shared with exec (because you have to fork first), but in some |
57 | overhead is often shared with exec (because you have to fork first), but |
37 | circumstances (e.g. when vfork is used), fork+exec can be much faster. |
58 | in some circumstances (e.g. when vfork is used), fork+exec can be much |
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59 | faster. |
38 | |
60 | |
39 | This module can help here by telling a small(er) helper process to fork, |
61 | This module can help here by telling a small(er) helper process to fork, |
40 | or fork+exec instead. |
62 | which is faster then forking the main process, and also uses vfork where |
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63 | possible. This gives the speed of vfork, with the flexibility of fork. |
41 | |
64 | |
42 | =item Forking usually creates a copy-on-write copy of the parent |
65 | =item Forking usually creates a copy-on-write copy of the parent |
43 | process. Memory (for example, modules or data files that have been |
66 | process. |
44 | will not take additional memory). When exec'ing a new process, modules |
67 | |
45 | and data files might need to be loaded again, at extra cpu and memory |
68 | For example, modules or data files that are loaded will not use additional |
46 | cost. Likewise when forking, all data structures are copied as well - if |
69 | memory after a fork. When exec'ing a new process, modules and data files |
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70 | might need to be loaded again, at extra CPU and memory cost. But when |
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71 | forking, literally all data structures are copied - if the program frees |
47 | the program frees them and replaces them by new data, the child processes |
72 | them and replaces them by new data, the child processes will retain the |
48 | will retain the memory even if it isn't used. |
73 | old version even if it isn't used, which can suddenly and unexpectedly |
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74 | increase memory usage when freeing memory. |
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75 | |
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76 | The trade-off is between more sharing with fork (which can be good or |
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77 | bad), and no sharing with exec. |
49 | |
78 | |
50 | This module allows the main program to do a controlled fork, and allows |
79 | This module allows the main program to do a controlled fork, and allows |
51 | modules to exec processes safely at any time. When creating a custom |
80 | modules to exec processes safely at any time. When creating a custom |
52 | process pool you can take advantage of data sharing via fork without |
81 | process pool you can take advantage of data sharing via fork without |
53 | risking to share large dynamic data structures that will blow up child |
82 | risking to share large dynamic data structures that will blow up child |
54 | memory usage. |
83 | memory usage. |
55 | |
84 | |
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85 | In other words, this module puts you into control over what is being |
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86 | shared and what isn't, at all times. |
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87 | |
56 | =item Exec'ing a new perl process might be difficult and slow. For |
88 | =item Exec'ing a new perl process might be difficult. |
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89 | |
57 | example, it is not easy to find the correct path to the perl interpreter, |
90 | For example, it is not easy to find the correct path to the perl |
58 | and all modules have to be loaded from disk again. Long running processes |
91 | interpreter - C<$^X> might not be a perl interpreter at all. |
59 | might run into problems when perl is upgraded for example. |
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60 | |
92 | |
61 | This module supports creating pre-initialised perl processes to be used |
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62 | as template, and also tries hard to identify the correct path to the perl |
93 | This module tries hard to identify the correct path to the perl |
63 | interpreter. With a cooperative main program, exec'ing the interpreter |
94 | interpreter. With a cooperative main program, exec'ing the interpreter |
64 | might not even be necessary. |
95 | might not even be necessary, but even without help from the main program, |
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96 | it will still work when used from a module. |
65 | |
97 | |
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98 | =item Exec'ing a new perl process might be slow, as all necessary modules |
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99 | have to be loaded from disk again, with no guarantees of success. |
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100 | |
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101 | Long running processes might run into problems when perl is upgraded |
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102 | and modules are no longer loadable because they refer to a different |
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103 | perl version, or parts of a distribution are newer than the ones already |
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104 | loaded. |
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105 | |
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106 | This module supports creating pre-initialised perl processes to be used as |
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107 | a template for new processes. |
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108 | |
66 | =item Forking might be impossible when a program is running. For example, |
109 | =item Forking might be impossible when a program is running. |
67 | POSIX makes it almost impossible to fork from a multithreaded program and |
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68 | do anything useful in the child - strictly speaking, if your perl program |
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69 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
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70 | you cannot call fork on the perl level anymore, at all. |
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71 | |
110 | |
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111 | For example, POSIX makes it almost impossible to fork from a |
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112 | multi-threaded program while doing anything useful in the child - in |
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113 | fact, if your perl program uses POSIX threads (even indirectly via |
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114 | e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level |
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115 | anymore without risking corruption issues on a number of operating |
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116 | systems. |
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117 | |
72 | This module can safely fork helper processes at any time, by caling |
118 | This module can safely fork helper processes at any time, by calling |
73 | fork+exec in C, in a POSIX-compatible way. |
119 | fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>). |
74 | |
120 | |
75 | =item Parallel processing with fork might be inconvenient or difficult |
121 | =item Parallel processing with fork might be inconvenient or difficult |
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122 | to implement. Modules might not work in both parent and child. |
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123 | |
76 | to implement. For example, when a program uses an event loop and creates |
124 | For example, when a program uses an event loop and creates watchers it |
77 | watchers it becomes very hard to use the event loop from a child |
125 | becomes very hard to use the event loop from a child program, as the |
78 | program, as the watchers already exist but are only meaningful in the |
126 | watchers already exist but are only meaningful in the parent. Worse, a |
79 | parent. Worse, a module might want to use such a system, not knowing |
127 | module might want to use such a module, not knowing whether another module |
80 | whether another module or the main program also does, leading to problems. |
128 | or the main program also does, leading to problems. |
81 | |
129 | |
82 | This module only lets the main program create pools by forking (because |
130 | Apart from event loops, graphical toolkits also commonly fall into the |
83 | only the main program can know when it is still safe to do so) - all other |
131 | "unsafe module" category, or just about anything that communicates with |
84 | pools are created by fork+exec, after which such modules can again be |
132 | the external world, such as network libraries and file I/O modules, which |
85 | loaded. |
133 | usually don't like being copied and then allowed to continue in two |
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134 | processes. |
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135 | |
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136 | With this module only the main program is allowed to create new processes |
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137 | by forking (because only the main program can know when it is still safe |
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138 | to do so) - all other processes are created via fork+exec, which makes it |
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139 | possible to use modules such as event loops or window interfaces safely. |
86 | |
140 | |
87 | =back |
141 | =back |
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142 | |
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143 | =head1 EXAMPLES |
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144 | |
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145 | =head2 Create a single new process, tell it to run your worker function. |
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146 | |
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147 | AnyEvent::Fork |
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148 | ->new |
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149 | ->require ("MyModule") |
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150 | ->run ("MyModule::worker, sub { |
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151 | my ($master_filehandle) = @_; |
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152 | |
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153 | # now $master_filehandle is connected to the |
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154 | # $slave_filehandle in the new process. |
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155 | }); |
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156 | |
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157 | C<MyModule> might look like this: |
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158 | |
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159 | package MyModule; |
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160 | |
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161 | sub worker { |
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162 | my ($slave_filehandle) = @_; |
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163 | |
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164 | # now $slave_filehandle is connected to the $master_filehandle |
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165 | # in the original prorcess. have fun! |
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166 | } |
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167 | |
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168 | =head2 Create a pool of server processes all accepting on the same socket. |
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169 | |
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170 | # create listener socket |
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171 | my $listener = ...; |
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172 | |
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173 | # create a pool template, initialise it and give it the socket |
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174 | my $pool = AnyEvent::Fork |
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175 | ->new |
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176 | ->require ("Some::Stuff", "My::Server") |
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177 | ->send_fh ($listener); |
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178 | |
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179 | # now create 10 identical workers |
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180 | for my $id (1..10) { |
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181 | $pool |
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182 | ->fork |
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183 | ->send_arg ($id) |
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184 | ->run ("My::Server::run"); |
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185 | } |
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186 | |
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187 | # now do other things - maybe use the filehandle provided by run |
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188 | # to wait for the processes to die. or whatever. |
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189 | |
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190 | C<My::Server> might look like this: |
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191 | |
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192 | package My::Server; |
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193 | |
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194 | sub run { |
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195 | my ($slave, $listener, $id) = @_; |
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196 | |
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197 | close $slave; # we do not use the socket, so close it to save resources |
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198 | |
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199 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
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200 | # or anything we usually couldn't do in a process forked normally. |
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201 | while (my $socket = $listener->accept) { |
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202 | # do sth. with new socket |
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203 | } |
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204 | } |
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205 | |
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206 | =head2 use AnyEvent::Fork as a faster fork+exec |
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207 | |
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208 | This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log |
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209 | and standard error redirected to the communications socket. It is usually |
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210 | faster than fork+exec, but still lets you prepare the environment. |
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211 | |
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212 | open my $output, ">/tmp/log" or die "$!"; |
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213 | |
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214 | AnyEvent::Fork |
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215 | ->new |
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216 | ->eval (' |
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217 | sub run { |
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218 | my ($fh, $output, @cmd) = @_; |
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219 | |
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220 | # perl will clear close-on-exec on STDOUT/STDERR |
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221 | open STDOUT, ">&", $output or die; |
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222 | open STDERR, ">&", $fh or die; |
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223 | |
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224 | exec @cmd; |
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225 | } |
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226 | ') |
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227 | ->send_fh ($output) |
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228 | ->send_arg ("/bin/echo", "hi") |
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229 | ->run ("run", my $cv = AE::cv); |
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230 | |
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231 | my $stderr = $cv->recv; |
88 | |
232 | |
89 | =head1 CONCEPTS |
233 | =head1 CONCEPTS |
90 | |
234 | |
91 | This module can create new processes either by executing a new perl |
235 | This module can create new processes either by executing a new perl |
92 | process, or by forking from an existing "template" process. |
236 | process, or by forking from an existing "template" process. |
… | |
… | |
109 | needed the first time. Forking from this process shares the memory used |
253 | needed the first time. Forking from this process shares the memory used |
110 | for the perl interpreter with the new process, but loading modules takes |
254 | for the perl interpreter with the new process, but loading modules takes |
111 | time, and the memory is not shared with anything else. |
255 | time, and the memory is not shared with anything else. |
112 | |
256 | |
113 | This is ideal for when you only need one extra process of a kind, with the |
257 | This is ideal for when you only need one extra process of a kind, with the |
114 | option of starting and stipping it on demand. |
258 | option of starting and stopping it on demand. |
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259 | |
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260 | Example: |
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261 | |
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262 | AnyEvent::Fork |
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263 | ->new |
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264 | ->require ("Some::Module") |
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265 | ->run ("Some::Module::run", sub { |
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266 | my ($fork_fh) = @_; |
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267 | }); |
115 | |
268 | |
116 | =item fork a new template process, load code, then fork processes off of |
269 | =item fork a new template process, load code, then fork processes off of |
117 | it and run the code |
270 | it and run the code |
118 | |
271 | |
119 | When you need to have a bunch of processes that all execute the same (or |
272 | When you need to have a bunch of processes that all execute the same (or |
… | |
… | |
125 | modules you loaded) is shared between the processes, and each new process |
278 | modules you loaded) is shared between the processes, and each new process |
126 | consumes relatively little memory of its own. |
279 | consumes relatively little memory of its own. |
127 | |
280 | |
128 | The disadvantage of this approach is that you need to create a template |
281 | The disadvantage of this approach is that you need to create a template |
129 | process for the sole purpose of forking new processes from it, but if you |
282 | process for the sole purpose of forking new processes from it, but if you |
130 | only need a fixed number of proceses you can create them, and then destroy |
283 | only need a fixed number of processes you can create them, and then destroy |
131 | the template process. |
284 | the template process. |
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285 | |
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286 | Example: |
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287 | |
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288 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
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289 | |
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290 | for (1..10) { |
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291 | $template->fork->run ("Some::Module::run", sub { |
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292 | my ($fork_fh) = @_; |
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293 | }); |
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294 | } |
|
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295 | |
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296 | # at this point, you can keep $template around to fork new processes |
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297 | # later, or you can destroy it, which causes it to vanish. |
132 | |
298 | |
133 | =item execute a new perl interpreter, load some code, run it |
299 | =item execute a new perl interpreter, load some code, run it |
134 | |
300 | |
135 | This is relatively slow, and doesn't allow you to share memory between |
301 | This is relatively slow, and doesn't allow you to share memory between |
136 | multiple processes. |
302 | multiple processes. |
… | |
… | |
138 | The only advantage is that you don't have to have a template process |
304 | The only advantage is that you don't have to have a template process |
139 | hanging around all the time to fork off some new processes, which might be |
305 | hanging around all the time to fork off some new processes, which might be |
140 | an advantage when there are long time spans where no extra processes are |
306 | an advantage when there are long time spans where no extra processes are |
141 | needed. |
307 | needed. |
142 | |
308 | |
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309 | Example: |
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310 | |
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311 | AnyEvent::Fork |
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312 | ->new_exec |
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313 | ->require ("Some::Module") |
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314 | ->run ("Some::Module::run", sub { |
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315 | my ($fork_fh) = @_; |
|
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316 | }); |
|
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317 | |
143 | =back |
318 | =back |
144 | |
319 | |
145 | =head1 FUNCTIONS |
320 | =head1 THE C<AnyEvent::Fork> CLASS |
|
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321 | |
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322 | This module exports nothing, and only implements a single class - |
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323 | C<AnyEvent::Fork>. |
|
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324 | |
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325 | There are two class constructors that both create new processes - C<new> |
|
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326 | and C<new_exec>. The C<fork> method creates a new process by forking an |
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327 | existing one and could be considered a third constructor. |
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328 | |
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329 | Most of the remaining methods deal with preparing the new process, by |
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330 | loading code, evaluating code and sending data to the new process. They |
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331 | usually return the process object, so you can chain method calls. |
|
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332 | |
|
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333 | If a process object is destroyed before calling its C<run> method, then |
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334 | the process simply exits. After C<run> is called, all responsibility is |
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335 | passed to the specified function. |
|
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336 | |
|
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337 | As long as there is any outstanding work to be done, process objects |
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338 | resist being destroyed, so there is no reason to store them unless you |
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339 | need them later - configure and forget works just fine. |
146 | |
340 | |
147 | =over 4 |
341 | =over 4 |
148 | |
342 | |
149 | =cut |
343 | =cut |
150 | |
344 | |
151 | package AnyEvent::Fork; |
345 | package AnyEvent::Fork; |
152 | |
346 | |
153 | use common::sense; |
347 | use common::sense; |
154 | |
348 | |
155 | use Socket (); |
349 | use Errno (); |
156 | |
350 | |
157 | use AnyEvent; |
351 | use AnyEvent; |
158 | use AnyEvent::Fork::Util; |
|
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159 | use AnyEvent::Util (); |
352 | use AnyEvent::Util (); |
160 | |
353 | |
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354 | use IO::FDPass; |
|
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355 | |
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356 | our $VERSION = 0.5; |
|
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357 | |
161 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
358 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
162 | |
|
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163 | =item my $pool = new AnyEvent::Fork key => value... |
|
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164 | |
|
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165 | Create a new process pool. The following named parameters are supported: |
|
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166 | |
359 | |
167 | =over 4 |
360 | =over 4 |
168 | |
361 | |
169 | =back |
362 | =back |
170 | |
363 | |
… | |
… | |
177 | our $TEMPLATE; |
370 | our $TEMPLATE; |
178 | |
371 | |
179 | sub _cmd { |
372 | sub _cmd { |
180 | my $self = shift; |
373 | my $self = shift; |
181 | |
374 | |
182 | # ideally, we would want to use "a (w/a)*" as format string, but perl versions |
375 | # ideally, we would want to use "a (w/a)*" as format string, but perl |
183 | # from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it. |
376 | # versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack |
184 | push @{ $self->[2] }, pack "N/a", pack "(w/a)*", @_; |
377 | # it. |
|
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378 | push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1]; |
185 | |
379 | |
186 | $self->[3] ||= AE::io $self->[1], 1, sub { |
380 | $self->[3] ||= AE::io $self->[1], 1, sub { |
|
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381 | do { |
|
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382 | # send the next "thing" in the queue - either a reference to an fh, |
|
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383 | # or a plain string. |
|
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384 | |
187 | if (ref $self->[2][0]) { |
385 | if (ref $self->[2][0]) { |
|
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386 | # send fh |
188 | AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] } |
387 | unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) { |
|
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388 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
|
|
389 | undef $self->[3]; |
|
|
390 | die "AnyEvent::Fork: file descriptor send failure: $!"; |
|
|
391 | } |
|
|
392 | |
189 | and shift @{ $self->[2] }; |
393 | shift @{ $self->[2] }; |
190 | |
394 | |
191 | } else { |
395 | } else { |
|
|
396 | # send string |
192 | my $len = syswrite $self->[1], $self->[2][0] |
397 | my $len = syswrite $self->[1], $self->[2][0]; |
|
|
398 | |
|
|
399 | unless ($len) { |
|
|
400 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
|
|
401 | undef $self->[3]; |
193 | or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" }; |
402 | die "AnyEvent::Fork: command write failure: $!"; |
|
|
403 | } |
194 | |
404 | |
195 | substr $self->[2][0], 0, $len, ""; |
405 | substr $self->[2][0], 0, $len, ""; |
196 | shift @{ $self->[2] } unless length $self->[2][0]; |
406 | shift @{ $self->[2] } unless length $self->[2][0]; |
197 | } |
407 | } |
|
|
408 | } while @{ $self->[2] }; |
198 | |
409 | |
199 | unless (@{ $self->[2] }) { |
410 | # everything written |
200 | undef $self->[3]; |
411 | undef $self->[3]; |
|
|
412 | |
|
|
413 | # invoke run callback, if any |
201 | $self->[0]->($self->[1]) if $self->[0]; |
414 | $self->[4]->($self->[1]) if $self->[4]; |
202 | } |
|
|
203 | }; |
415 | }; |
|
|
416 | |
|
|
417 | () # make sure we don't leak the watcher |
204 | } |
418 | } |
205 | |
419 | |
206 | sub _new { |
420 | sub _new { |
207 | my ($self, $fh) = @_; |
421 | my ($self, $fh, $pid) = @_; |
208 | |
422 | |
209 | AnyEvent::Util::fh_nonblocking $fh, 1; |
423 | AnyEvent::Util::fh_nonblocking $fh, 1; |
210 | |
424 | |
211 | $self = bless [ |
425 | $self = bless [ |
212 | undef, # run callback |
426 | $pid, |
213 | $fh, |
427 | $fh, |
214 | [], # write queue - strings or fd's |
428 | [], # write queue - strings or fd's |
215 | undef, # AE watcher |
429 | undef, # AE watcher |
216 | ], $self; |
430 | ], $self; |
217 | |
431 | |
218 | # my ($a, $b) = AnyEvent::Util::portable_socketpair; |
|
|
219 | |
|
|
220 | # queue_cmd $template, "Iabc"; |
|
|
221 | # push @{ $template->[2] }, \$b; |
|
|
222 | |
|
|
223 | # use Coro::AnyEvent; Coro::AnyEvent::sleep 1; |
|
|
224 | # undef $b; |
|
|
225 | # die "x" . <$a>; |
|
|
226 | |
|
|
227 | $self |
432 | $self |
228 | } |
433 | } |
229 | |
434 | |
230 | # fork template from current process, used by AnyEvent::Fork::Early/Template |
435 | # fork template from current process, used by AnyEvent::Fork::Early/Template |
231 | sub _new_fork { |
436 | sub _new_fork { |
232 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
437 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
|
|
438 | my $parent = $$; |
|
|
439 | |
233 | my $pid = fork; |
440 | my $pid = fork; |
234 | |
441 | |
235 | if ($pid eq 0) { |
442 | if ($pid eq 0) { |
236 | require AnyEvent::Fork::Serve; |
443 | require AnyEvent::Fork::Serve; |
|
|
444 | $AnyEvent::Fork::Serve::OWNER = $parent; |
237 | close $fh; |
445 | close $fh; |
|
|
446 | $0 = "$_[1] of $parent"; |
|
|
447 | $SIG{CHLD} = 'IGNORE'; |
238 | AnyEvent::Fork::Serve::serve ($slave); |
448 | AnyEvent::Fork::Serve::serve ($slave); |
239 | AnyEvent::Fork::Util::_exit 0; |
449 | exit 0; |
240 | } elsif (!$pid) { |
450 | } elsif (!$pid) { |
241 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
451 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
242 | } |
452 | } |
243 | |
453 | |
244 | AnyEvent::Fork->_new ($fh) |
454 | AnyEvent::Fork->_new ($fh, $pid) |
245 | } |
455 | } |
246 | |
456 | |
247 | =item my $proc = new AnyEvent::Fork |
457 | =item my $proc = new AnyEvent::Fork |
248 | |
458 | |
249 | Create a new "empty" perl interpreter process and returns its process |
459 | Create a new "empty" perl interpreter process and returns its process |
250 | object for further manipulation. |
460 | object for further manipulation. |
251 | |
461 | |
252 | The new process is forked from a template process that is kept around |
462 | The new process is forked from a template process that is kept around |
253 | for this purpose. When it doesn't exist yet, it is created by a call to |
463 | for this purpose. When it doesn't exist yet, it is created by a call to |
254 | C<new_exec> and kept around for future calls. |
464 | C<new_exec> first and then stays around for future calls. |
255 | |
465 | |
256 | =cut |
466 | =cut |
257 | |
467 | |
258 | sub new { |
468 | sub new { |
259 | my $class = shift; |
469 | my $class = shift; |
… | |
… | |
295 | reduces the amount of memory sharing that is possible, and is also slower. |
505 | reduces the amount of memory sharing that is possible, and is also slower. |
296 | |
506 | |
297 | You should use C<new> whenever possible, except when having a template |
507 | You should use C<new> whenever possible, except when having a template |
298 | process around is unacceptable. |
508 | process around is unacceptable. |
299 | |
509 | |
300 | The path to the perl interpreter is divined usign various methods - first |
510 | The path to the perl interpreter is divined using various methods - first |
301 | C<$^X> is investigated to see if the path ends with something that sounds |
511 | C<$^X> is investigated to see if the path ends with something that sounds |
302 | as if it were the perl interpreter. Failing this, the module falls back to |
512 | as if it were the perl interpreter. Failing this, the module falls back to |
303 | using C<$Config::Config{perlpath}>. |
513 | using C<$Config::Config{perlpath}>. |
304 | |
514 | |
305 | =cut |
515 | =cut |
… | |
… | |
314 | my $perl = $; |
524 | my $perl = $; |
315 | |
525 | |
316 | # first we try $^X, but the path must be absolute (always on win32), and end in sth. |
526 | # first we try $^X, but the path must be absolute (always on win32), and end in sth. |
317 | # that looks like perl. this obviously only works for posix and win32 |
527 | # that looks like perl. this obviously only works for posix and win32 |
318 | unless ( |
528 | unless ( |
319 | (AnyEvent::Fork::Util::WIN32 || $perl =~ m%^/%) |
529 | ($^O eq "MSWin32" || $perl =~ m%^/%) |
320 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
530 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
321 | ) { |
531 | ) { |
322 | # if it doesn't look perlish enough, try Config |
532 | # if it doesn't look perlish enough, try Config |
323 | require Config; |
533 | require Config; |
324 | $perl = $Config::Config{perlpath}; |
534 | $perl = $Config::Config{perlpath}; |
… | |
… | |
328 | require Proc::FastSpawn; |
538 | require Proc::FastSpawn; |
329 | |
539 | |
330 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
540 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
331 | Proc::FastSpawn::fd_inherit (fileno $slave); |
541 | Proc::FastSpawn::fd_inherit (fileno $slave); |
332 | |
542 | |
|
|
543 | # new fh's should always be set cloexec (due to $^F), |
|
|
544 | # but hey, not on win32, so we always clear the inherit flag. |
|
|
545 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
|
|
546 | |
333 | # quick. also doesn't work in win32. of course. what did you expect |
547 | # quick. also doesn't work in win32. of course. what did you expect |
334 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
548 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
335 | my %env = %ENV; |
549 | my %env = %ENV; |
336 | $env{PERL5LIB} = join ":", grep !ref, @INC; |
550 | $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; |
337 | |
551 | |
338 | Proc::FastSpawn::spawn ( |
552 | my $pid = Proc::FastSpawn::spawn ( |
339 | $perl, |
553 | $perl, |
340 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave], |
554 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
341 | [map "$_=$env{$_}", keys %env], |
555 | [map "$_=$env{$_}", keys %env], |
342 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
556 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
343 | |
557 | |
344 | $self->_new ($fh) |
558 | $self->_new ($fh, $pid) |
|
|
559 | } |
|
|
560 | |
|
|
561 | =item $pid = $proc->pid |
|
|
562 | |
|
|
563 | Returns the process id of the process I<iff it is a direct child of the |
|
|
564 | process running AnyEvent::Fork>, and C<undef> otherwise. |
|
|
565 | |
|
|
566 | Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and |
|
|
567 | L<AnyEvent::Fork::Template> are direct children, and you are responsible |
|
|
568 | to clean up their zombies when they die. |
|
|
569 | |
|
|
570 | All other processes are not direct children, and will be cleaned up by |
|
|
571 | AnyEvent::Fork itself. |
|
|
572 | |
|
|
573 | =cut |
|
|
574 | |
|
|
575 | sub pid { |
|
|
576 | $_[0][0] |
|
|
577 | } |
|
|
578 | |
|
|
579 | =item $proc = $proc->eval ($perlcode, @args) |
|
|
580 | |
|
|
581 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
|
|
582 | the strings specified by C<@args>, in the "main" package. |
|
|
583 | |
|
|
584 | This call is meant to do any custom initialisation that might be required |
|
|
585 | (for example, the C<require> method uses it). It's not supposed to be used |
|
|
586 | to completely take over the process, use C<run> for that. |
|
|
587 | |
|
|
588 | The code will usually be executed after this call returns, and there is no |
|
|
589 | way to pass anything back to the calling process. Any evaluation errors |
|
|
590 | will be reported to stderr and cause the process to exit. |
|
|
591 | |
|
|
592 | If you want to execute some code (that isn't in a module) to take over the |
|
|
593 | process, you should compile a function via C<eval> first, and then call |
|
|
594 | it via C<run>. This also gives you access to any arguments passed via the |
|
|
595 | C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as |
|
|
596 | a faster fork+exec> example to see it in action. |
|
|
597 | |
|
|
598 | Returns the process object for easy chaining of method calls. |
|
|
599 | |
|
|
600 | =cut |
|
|
601 | |
|
|
602 | sub eval { |
|
|
603 | my ($self, $code, @args) = @_; |
|
|
604 | |
|
|
605 | $self->_cmd (e => pack "(w/a*)*", $code, @args); |
|
|
606 | |
|
|
607 | $self |
345 | } |
608 | } |
346 | |
609 | |
347 | =item $proc = $proc->require ($module, ...) |
610 | =item $proc = $proc->require ($module, ...) |
348 | |
611 | |
349 | Tries to load the given modules into the process |
612 | Tries to load the given module(s) into the process |
350 | |
613 | |
351 | Returns the process object for easy chaining of method calls. |
614 | Returns the process object for easy chaining of method calls. |
|
|
615 | |
|
|
616 | =cut |
|
|
617 | |
|
|
618 | sub require { |
|
|
619 | my ($self, @modules) = @_; |
|
|
620 | |
|
|
621 | s%::%/%g for @modules; |
|
|
622 | $self->eval ('require "$_.pm" for @_', @modules); |
|
|
623 | |
|
|
624 | $self |
|
|
625 | } |
352 | |
626 | |
353 | =item $proc = $proc->send_fh ($handle, ...) |
627 | =item $proc = $proc->send_fh ($handle, ...) |
354 | |
628 | |
355 | Send one or more file handles (I<not> file descriptors) to the process, |
629 | Send one or more file handles (I<not> file descriptors) to the process, |
356 | to prepare a call to C<run>. |
630 | to prepare a call to C<run>. |
357 | |
631 | |
358 | The process object keeps a reference to the handles until this is done, |
632 | The process object keeps a reference to the handles until they have |
359 | so you must not explicitly close the handles. This is most easily |
633 | been passed over to the process, so you must not explicitly close the |
360 | accomplished by simply not storing the file handles anywhere after passing |
634 | handles. This is most easily accomplished by simply not storing the file |
361 | them to this method. |
635 | handles anywhere after passing them to this method - when AnyEvent::Fork |
|
|
636 | is finished using them, perl will automatically close them. |
362 | |
637 | |
363 | Returns the process object for easy chaining of method calls. |
638 | Returns the process object for easy chaining of method calls. |
|
|
639 | |
|
|
640 | Example: pass a file handle to a process, and release it without |
|
|
641 | closing. It will be closed automatically when it is no longer used. |
|
|
642 | |
|
|
643 | $proc->send_fh ($my_fh); |
|
|
644 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
364 | |
645 | |
365 | =cut |
646 | =cut |
366 | |
647 | |
367 | sub send_fh { |
648 | sub send_fh { |
368 | my ($self, @fh) = @_; |
649 | my ($self, @fh) = @_; |
… | |
… | |
376 | } |
657 | } |
377 | |
658 | |
378 | =item $proc = $proc->send_arg ($string, ...) |
659 | =item $proc = $proc->send_arg ($string, ...) |
379 | |
660 | |
380 | Send one or more argument strings to the process, to prepare a call to |
661 | Send one or more argument strings to the process, to prepare a call to |
381 | C<run>. The strings can be any octet string. |
662 | C<run>. The strings can be any octet strings. |
382 | |
663 | |
|
|
664 | The protocol is optimised to pass a moderate number of relatively short |
|
|
665 | strings - while you can pass up to 4GB of data in one go, this is more |
|
|
666 | meant to pass some ID information or other startup info, not big chunks of |
|
|
667 | data. |
|
|
668 | |
383 | Returns the process object for easy chaining of emthod calls. |
669 | Returns the process object for easy chaining of method calls. |
384 | |
670 | |
385 | =cut |
671 | =cut |
386 | |
672 | |
387 | sub send_arg { |
673 | sub send_arg { |
388 | my ($self, @arg) = @_; |
674 | my ($self, @arg) = @_; |
389 | |
675 | |
390 | $self->_cmd (a => @arg); |
676 | $self->_cmd (a => pack "(w/a*)*", @arg); |
391 | |
677 | |
392 | $self |
678 | $self |
393 | } |
679 | } |
394 | |
680 | |
395 | =item $proc->run ($func, $cb->($fh)) |
681 | =item $proc->run ($func, $cb->($fh)) |
396 | |
682 | |
397 | Enter the function specified by the fully qualified name in C<$func> in |
683 | Enter the function specified by the function name in C<$func> in the |
398 | the process. The function is called with the communication socket as first |
684 | process. The function is called with the communication socket as first |
399 | argument, followed by all file handles and string arguments sent earlier |
685 | argument, followed by all file handles and string arguments sent earlier |
400 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
686 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
401 | |
687 | |
402 | If the called function returns, the process exits. |
|
|
403 | |
|
|
404 | Preparing the process can take time - when the process is ready, the |
|
|
405 | callback is invoked with the local communications socket as argument. |
|
|
406 | |
|
|
407 | The process object becomes unusable on return from this function. |
688 | The process object becomes unusable on return from this function - any |
|
|
689 | further method calls result in undefined behaviour. |
|
|
690 | |
|
|
691 | The function name should be fully qualified, but if it isn't, it will be |
|
|
692 | looked up in the C<main> package. |
|
|
693 | |
|
|
694 | If the called function returns, doesn't exist, or any error occurs, the |
|
|
695 | process exits. |
|
|
696 | |
|
|
697 | Preparing the process is done in the background - when all commands have |
|
|
698 | been sent, the callback is invoked with the local communications socket |
|
|
699 | as argument. At this point you can start using the socket in any way you |
|
|
700 | like. |
408 | |
701 | |
409 | If the communication socket isn't used, it should be closed on both sides, |
702 | If the communication socket isn't used, it should be closed on both sides, |
410 | to save on kernel memory. |
703 | to save on kernel memory. |
411 | |
704 | |
412 | The socket is non-blocking in the parent, and blocking in the newly |
705 | The socket is non-blocking in the parent, and blocking in the newly |
413 | created process. The close-on-exec flag is set on both. Even if not used |
706 | created process. The close-on-exec flag is set in both. |
|
|
707 | |
414 | otherwise, the socket can be a good indicator for the existance of the |
708 | Even if not used otherwise, the socket can be a good indicator for the |
415 | process - if the othe rprocess exits, you get a readable event on it, |
709 | existence of the process - if the other process exits, you get a readable |
416 | because exiting the process closes the socket (if it didn't create any |
710 | event on it, because exiting the process closes the socket (if it didn't |
417 | children using fork). |
711 | create any children using fork). |
|
|
712 | |
|
|
713 | Example: create a template for a process pool, pass a few strings, some |
|
|
714 | file handles, then fork, pass one more string, and run some code. |
|
|
715 | |
|
|
716 | my $pool = AnyEvent::Fork |
|
|
717 | ->new |
|
|
718 | ->send_arg ("str1", "str2") |
|
|
719 | ->send_fh ($fh1, $fh2); |
|
|
720 | |
|
|
721 | for (1..2) { |
|
|
722 | $pool |
|
|
723 | ->fork |
|
|
724 | ->send_arg ("str3") |
|
|
725 | ->run ("Some::function", sub { |
|
|
726 | my ($fh) = @_; |
|
|
727 | |
|
|
728 | # fh is nonblocking, but we trust that the OS can accept these |
|
|
729 | # few octets anyway. |
|
|
730 | syswrite $fh, "hi #$_\n"; |
|
|
731 | |
|
|
732 | # $fh is being closed here, as we don't store it anywhere |
|
|
733 | }); |
|
|
734 | } |
|
|
735 | |
|
|
736 | # Some::function might look like this - all parameters passed before fork |
|
|
737 | # and after will be passed, in order, after the communications socket. |
|
|
738 | sub Some::function { |
|
|
739 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
|
|
740 | |
|
|
741 | print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order |
|
|
742 | } |
418 | |
743 | |
419 | =cut |
744 | =cut |
420 | |
745 | |
421 | sub run { |
746 | sub run { |
422 | my ($self, $func, $cb) = @_; |
747 | my ($self, $func, $cb) = @_; |
423 | |
748 | |
424 | $self->[0] = $cb; |
749 | $self->[4] = $cb; |
425 | $self->_cmd ("r", $func); |
750 | $self->_cmd (r => $func); |
426 | } |
751 | } |
427 | |
752 | |
428 | =back |
753 | =back |
|
|
754 | |
|
|
755 | =head1 PERFORMANCE |
|
|
756 | |
|
|
757 | Now for some unscientific benchmark numbers (all done on an amd64 |
|
|
758 | GNU/Linux box). These are intended to give you an idea of the relative |
|
|
759 | performance you can expect, they are not meant to be absolute performance |
|
|
760 | numbers. |
|
|
761 | |
|
|
762 | OK, so, I ran a simple benchmark that creates a socket pair, forks, calls |
|
|
763 | exit in the child and waits for the socket to close in the parent. I did |
|
|
764 | load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB. |
|
|
765 | |
|
|
766 | 2079 new processes per second, using manual socketpair + fork |
|
|
767 | |
|
|
768 | Then I did the same thing, but instead of calling fork, I called |
|
|
769 | AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the |
|
|
770 | socket form the child to close on exit. This does the same thing as manual |
|
|
771 | socket pair + fork, except that what is forked is the template process |
|
|
772 | (2440kB), and the socket needs to be passed to the server at the other end |
|
|
773 | of the socket first. |
|
|
774 | |
|
|
775 | 2307 new processes per second, using AnyEvent::Fork->new |
|
|
776 | |
|
|
777 | And finally, using C<new_exec> instead C<new>, using vforks+execs to exec |
|
|
778 | a new perl interpreter and compile the small server each time, I get: |
|
|
779 | |
|
|
780 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
|
|
781 | |
|
|
782 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
|
|
783 | though it uses the same operations, but adds a lot of overhead? |
|
|
784 | |
|
|
785 | The difference is simply the process size: forking the 5MB process takes |
|
|
786 | so much longer than forking the 2.5MB template process that the extra |
|
|
787 | overhead introduced is canceled out. |
|
|
788 | |
|
|
789 | If the benchmark process grows, the normal fork becomes even slower: |
|
|
790 | |
|
|
791 | 1340 new processes, manual fork of a 20MB process |
|
|
792 | 731 new processes, manual fork of a 200MB process |
|
|
793 | 235 new processes, manual fork of a 2000MB process |
|
|
794 | |
|
|
795 | What that means (to me) is that I can use this module without having a bad |
|
|
796 | conscience because of the extra overhead required to start new processes. |
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|
797 | |
|
|
798 | =head1 TYPICAL PROBLEMS |
|
|
799 | |
|
|
800 | This section lists typical problems that remain. I hope by recognising |
|
|
801 | them, most can be avoided. |
|
|
802 | |
|
|
803 | =over 4 |
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|
804 | |
|
|
805 | =item leaked file descriptors for exec'ed processes |
|
|
806 | |
|
|
807 | POSIX systems inherit file descriptors by default when exec'ing a new |
|
|
808 | process. While perl itself laudably sets the close-on-exec flags on new |
|
|
809 | file handles, most C libraries don't care, and even if all cared, it's |
|
|
810 | often not possible to set the flag in a race-free manner. |
|
|
811 | |
|
|
812 | That means some file descriptors can leak through. And since it isn't |
|
|
813 | possible to know which file descriptors are "good" and "necessary" (or |
|
|
814 | even to know which file descriptors are open), there is no good way to |
|
|
815 | close the ones that might harm. |
|
|
816 | |
|
|
817 | As an example of what "harm" can be done consider a web server that |
|
|
818 | accepts connections and afterwards some module uses AnyEvent::Fork for the |
|
|
819 | first time, causing it to fork and exec a new process, which might inherit |
|
|
820 | the network socket. When the server closes the socket, it is still open |
|
|
821 | in the child (which doesn't even know that) and the client might conclude |
|
|
822 | that the connection is still fine. |
|
|
823 | |
|
|
824 | For the main program, there are multiple remedies available - |
|
|
825 | L<AnyEvent::Fork::Early> is one, creating a process early and not using |
|
|
826 | C<new_exec> is another, as in both cases, the first process can be exec'ed |
|
|
827 | well before many random file descriptors are open. |
|
|
828 | |
|
|
829 | In general, the solution for these kind of problems is to fix the |
|
|
830 | libraries or the code that leaks those file descriptors. |
|
|
831 | |
|
|
832 | Fortunately, most of these leaked descriptors do no harm, other than |
|
|
833 | sitting on some resources. |
|
|
834 | |
|
|
835 | =item leaked file descriptors for fork'ed processes |
|
|
836 | |
|
|
837 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
|
|
838 | which closes file descriptors not marked for being inherited. |
|
|
839 | |
|
|
840 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
|
|
841 | a way to create these processes by forking, and this leaks more file |
|
|
842 | descriptors than exec'ing them, as there is no way to mark descriptors as |
|
|
843 | "close on fork". |
|
|
844 | |
|
|
845 | An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create |
|
|
846 | pipes for internal uses, and L<Gtk2> might open a connection to the X |
|
|
847 | server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have |
|
|
848 | trouble with a fork. |
|
|
849 | |
|
|
850 | The solution is to either not load these modules before use'ing |
|
|
851 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
|
|
852 | initialising them, for example, by calling C<init Gtk2> manually. |
|
|
853 | |
|
|
854 | =item exiting calls object destructors |
|
|
855 | |
|
|
856 | This only applies to users of L<AnyEvent::Fork:Early> and |
|
|
857 | L<AnyEvent::Fork::Template>, or when initialiasing code creates objects |
|
|
858 | that reference external resources. |
|
|
859 | |
|
|
860 | When a process created by AnyEvent::Fork exits, it might do so by calling |
|
|
861 | exit, or simply letting perl reach the end of the program. At which point |
|
|
862 | Perl runs all destructors. |
|
|
863 | |
|
|
864 | Not all destructors are fork-safe - for example, an object that represents |
|
|
865 | the connection to an X display might tell the X server to free resources, |
|
|
866 | which is inconvenient when the "real" object in the parent still needs to |
|
|
867 | use them. |
|
|
868 | |
|
|
869 | This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used |
|
|
870 | it as the very first thing, right? |
|
|
871 | |
|
|
872 | It is a problem for L<AnyEvent::Fork::Template> though - and the solution |
|
|
873 | is to not create objects with nontrivial destructors that might have an |
|
|
874 | effect outside of Perl. |
|
|
875 | |
|
|
876 | =back |
|
|
877 | |
|
|
878 | =head1 PORTABILITY NOTES |
|
|
879 | |
|
|
880 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
|
|
881 | and ::Template is not going to work), and it cost a lot of blood and sweat |
|
|
882 | to make it so, mostly due to the bloody broken perl that nobody seems to |
|
|
883 | care about. The fork emulation is a bad joke - I have yet to see something |
|
|
884 | useful that you can do with it without running into memory corruption |
|
|
885 | issues or other braindamage. Hrrrr. |
|
|
886 | |
|
|
887 | Cygwin perl is not supported at the moment due to some hilarious |
|
|
888 | shortcomings of its API - see L<IO::FDPoll> for more details. |
|
|
889 | |
|
|
890 | =head1 SEE ALSO |
|
|
891 | |
|
|
892 | L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
|
|
893 | L<AnyEvent::Fork::Template> (to create a process by forking the main |
|
|
894 | program at a convenient time). |
429 | |
895 | |
430 | =head1 AUTHOR |
896 | =head1 AUTHOR |
431 | |
897 | |
432 | Marc Lehmann <schmorp@schmorp.de> |
898 | Marc Lehmann <schmorp@schmorp.de> |
433 | http://home.schmorp.de/ |
899 | http://home.schmorp.de/ |