… | |
… | |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use AnyEvent::Fork; |
7 | use AnyEvent::Fork; |
8 | |
8 | |
9 | ################################################################## |
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; |
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15 | |
|
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16 | =head1 DESCRIPTION |
|
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17 | |
|
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18 | This module allows you to create new processes, without actually forking |
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|
19 | them from your current process (avoiding the problems of forking), but |
|
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20 | preserving most of the advantages of fork. |
|
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21 | |
|
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22 | It can be used to create new worker processes or new independent |
|
|
23 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
|
|
24 | in pre-forked servers) but also to spawn new external processes (such as |
|
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25 | CGI scripts from a web server), which can be faster (and more well behaved) |
|
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26 | than using fork+exec in big processes. |
|
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27 | |
|
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28 | Special care has been taken to make this module useful from other modules, |
|
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29 | while still supporting specialised environments such as L<App::Staticperl> |
|
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30 | or L<PAR::Packer>. |
|
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31 | |
|
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32 | =head2 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 | |
|
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45 | =head2 COMPARISON TO OTHER MODULES |
|
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46 | |
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47 | There is an abundance of modules on CPAN that do "something fork", such as |
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48 | L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker> |
|
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49 | or L<AnyEvent::Subprocess>. There are modules that implement their own |
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50 | process management, such as L<AnyEvent::DBI>. |
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51 | |
|
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52 | The problems that all these modules try to solve are real, however, none |
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53 | of them (from what I have seen) tackle the very real problems of unwanted |
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54 | memory sharing, efficiency, not being able to use event processing or |
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55 | similar modules in the processes they create. |
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56 | |
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57 | This module doesn't try to replace any of them - instead it tries to solve |
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58 | the problem of creating processes with a minimum of fuss and overhead (and |
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59 | also luxury). Ideally, most of these would use AnyEvent::Fork internally, |
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60 | except they were written before AnyEvent:Fork was available, so obviously |
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61 | had to roll their own. |
|
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62 | |
|
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63 | =head2 PROBLEM STATEMENT |
|
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64 | |
|
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65 | There are two traditional ways to implement parallel processing on UNIX |
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66 | like operating systems - fork and process, and fork+exec and process. They |
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67 | have different advantages and disadvantages that I describe below, |
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68 | together with how this module tries to mitigate the disadvantages. |
|
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69 | |
|
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70 | =over 4 |
|
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71 | |
|
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72 | =item Forking from a big process can be very slow. |
|
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73 | |
|
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74 | A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This |
|
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75 | overhead is often shared with exec (because you have to fork first), but |
|
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76 | in some circumstances (e.g. when vfork is used), fork+exec can be much |
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77 | faster. |
|
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78 | |
|
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79 | This module can help here by telling a small(er) helper process to fork, |
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80 | which is faster then forking the main process, and also uses vfork where |
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81 | possible. This gives the speed of vfork, with the flexibility of fork. |
|
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82 | |
|
|
83 | =item Forking usually creates a copy-on-write copy of the parent |
|
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84 | process. |
|
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85 | |
|
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86 | For example, modules or data files that are loaded will not use additional |
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87 | memory after a fork. When exec'ing a new process, modules and data files |
|
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88 | might need to be loaded again, at extra CPU and memory cost. But when |
|
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89 | forking, literally all data structures are copied - if the program frees |
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90 | them and replaces them by new data, the child processes will retain the |
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91 | old version even if it isn't used, which can suddenly and unexpectedly |
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92 | increase memory usage when freeing memory. |
|
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93 | |
|
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94 | The trade-off is between more sharing with fork (which can be good or |
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95 | bad), and no sharing with exec. |
|
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96 | |
|
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97 | This module allows the main program to do a controlled fork, and allows |
|
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98 | modules to exec processes safely at any time. When creating a custom |
|
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99 | process pool you can take advantage of data sharing via fork without |
|
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100 | risking to share large dynamic data structures that will blow up child |
|
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101 | memory usage. |
|
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102 | |
|
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103 | In other words, this module puts you into control over what is being |
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104 | shared and what isn't, at all times. |
|
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105 | |
|
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106 | =item Exec'ing a new perl process might be difficult. |
|
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107 | |
|
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108 | For example, it is not easy to find the correct path to the perl |
|
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109 | interpreter - C<$^X> might not be a perl interpreter at all. |
|
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110 | |
|
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111 | This module tries hard to identify the correct path to the perl |
|
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112 | interpreter. With a cooperative main program, exec'ing the interpreter |
|
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113 | might not even be necessary, but even without help from the main program, |
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114 | it will still work when used from a module. |
|
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115 | |
|
|
116 | =item Exec'ing a new perl process might be slow, as all necessary modules |
|
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117 | have to be loaded from disk again, with no guarantees of success. |
|
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118 | |
|
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119 | Long running processes might run into problems when perl is upgraded |
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120 | and modules are no longer loadable because they refer to a different |
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121 | perl version, or parts of a distribution are newer than the ones already |
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122 | loaded. |
|
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123 | |
|
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124 | This module supports creating pre-initialised perl processes to be used as |
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125 | a template for new processes. |
|
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126 | |
|
|
127 | =item Forking might be impossible when a program is running. |
|
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128 | |
|
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129 | For example, POSIX makes it almost impossible to fork from a |
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130 | multi-threaded program while doing anything useful in the child - in |
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131 | fact, if your perl program uses POSIX threads (even indirectly via |
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132 | e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level |
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133 | anymore without risking corruption issues on a number of operating |
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134 | systems. |
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135 | |
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136 | This module can safely fork helper processes at any time, by calling |
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137 | fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>). |
|
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138 | |
|
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139 | =item Parallel processing with fork might be inconvenient or difficult |
|
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140 | to implement. Modules might not work in both parent and child. |
|
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141 | |
|
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142 | For example, when a program uses an event loop and creates watchers it |
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143 | becomes very hard to use the event loop from a child program, as the |
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144 | watchers already exist but are only meaningful in the parent. Worse, a |
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145 | module might want to use such a module, not knowing whether another module |
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146 | or the main program also does, leading to problems. |
|
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147 | |
|
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148 | Apart from event loops, graphical toolkits also commonly fall into the |
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149 | "unsafe module" category, or just about anything that communicates with |
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150 | the external world, such as network libraries and file I/O modules, which |
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151 | usually don't like being copied and then allowed to continue in two |
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152 | processes. |
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153 | |
|
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154 | With this module only the main program is allowed to create new processes |
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155 | by forking (because only the main program can know when it is still safe |
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156 | to do so) - all other processes are created via fork+exec, which makes it |
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157 | possible to use modules such as event loops or window interfaces safely. |
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158 | |
|
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159 | =back |
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160 | |
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161 | =head1 EXAMPLES |
|
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162 | |
10 | # create a single new process, tell it to run your worker function |
163 | =head2 Create a single new process, tell it to run your worker function. |
11 | |
164 | |
12 | AnyEvent::Fork |
165 | AnyEvent::Fork |
13 | ->new |
166 | ->new |
14 | ->require ("MyModule") |
167 | ->require ("MyModule") |
15 | ->run ("MyModule::worker, sub { |
168 | ->run ("MyModule::worker, sub { |
… | |
… | |
17 | |
170 | |
18 | # now $master_filehandle is connected to the |
171 | # now $master_filehandle is connected to the |
19 | # $slave_filehandle in the new process. |
172 | # $slave_filehandle in the new process. |
20 | }); |
173 | }); |
21 | |
174 | |
22 | # MyModule::worker might look like this |
175 | C<MyModule> might look like this: |
|
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176 | |
|
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177 | package MyModule; |
|
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178 | |
23 | sub MyModule::worker { |
179 | sub worker { |
24 | my ($slave_filehandle) = @_; |
180 | my ($slave_filehandle) = @_; |
25 | |
181 | |
26 | # now $slave_filehandle is connected to the $master_filehandle |
182 | # now $slave_filehandle is connected to the $master_filehandle |
27 | # in the original prorcess. have fun! |
183 | # in the original prorcess. have fun! |
28 | } |
184 | } |
29 | |
185 | |
30 | ################################################################## |
|
|
31 | # create a pool of server processes all accepting on the same socket |
186 | =head2 Create a pool of server processes all accepting on the same socket. |
32 | |
187 | |
33 | # create listener socket |
188 | # create listener socket |
34 | my $listener = ...; |
189 | my $listener = ...; |
35 | |
190 | |
36 | # create a pool template, initialise it and give it the socket |
191 | # create a pool template, initialise it and give it the socket |
… | |
… | |
48 | } |
203 | } |
49 | |
204 | |
50 | # now do other things - maybe use the filehandle provided by run |
205 | # now do other things - maybe use the filehandle provided by run |
51 | # to wait for the processes to die. or whatever. |
206 | # to wait for the processes to die. or whatever. |
52 | |
207 | |
53 | # My::Server::run might look like this |
208 | C<My::Server> might look like this: |
54 | sub My::Server::run { |
209 | |
|
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210 | package My::Server; |
|
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211 | |
|
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212 | sub run { |
55 | my ($slave, $listener, $id) = @_; |
213 | my ($slave, $listener, $id) = @_; |
56 | |
214 | |
57 | close $slave; # we do not use the socket, so close it to save resources |
215 | close $slave; # we do not use the socket, so close it to save resources |
58 | |
216 | |
59 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
217 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
… | |
… | |
61 | while (my $socket = $listener->accept) { |
219 | while (my $socket = $listener->accept) { |
62 | # do sth. with new socket |
220 | # do sth. with new socket |
63 | } |
221 | } |
64 | } |
222 | } |
65 | |
223 | |
66 | =head1 DESCRIPTION |
224 | =head2 use AnyEvent::Fork as a faster fork+exec |
67 | |
225 | |
68 | This module allows you to create new processes, without actually forking |
226 | This runs C</bin/echo hi>, with stdandard output redirected to /tmp/log |
69 | them from your current process (avoiding the problems of forking), but |
227 | and standard error redirected to the communications socket. It is usually |
70 | preserving most of the advantages of fork. |
228 | faster than fork+exec, but still lets you prepare the environment. |
71 | |
229 | |
72 | It can be used to create new worker processes or new independent |
230 | open my $output, ">/tmp/log" or die "$!"; |
73 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
|
|
74 | in pre-forked servers) but also to spawn new external processes (such as |
|
|
75 | CGI scripts from a web server), which can be faster (and more well behaved) |
|
|
76 | than using fork+exec in big processes. |
|
|
77 | |
231 | |
78 | Special care has been taken to make this module useful from other modules, |
232 | AnyEvent::Fork |
79 | while still supporting specialised environments such as L<App::Staticperl> |
233 | ->new |
80 | or L<PAR::Packer>. |
234 | ->eval (' |
|
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235 | sub run { |
|
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236 | my ($fh, $output, @cmd) = @_; |
81 | |
237 | |
82 | =head1 WHAT THIS MODULE IS NOT |
238 | # perl will clear close-on-exec on STDOUT/STDERR |
|
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239 | open STDOUT, ">&", $output or die; |
|
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240 | open STDERR, ">&", $fh or die; |
83 | |
241 | |
84 | This module only creates processes and lets you pass file handles and |
242 | exec @cmd; |
85 | strings to it, and run perl code. It does not implement any kind of RPC - |
243 | } |
86 | there is no back channel from the process back to you, and there is no RPC |
244 | ') |
87 | or message passing going on. |
245 | ->send_fh ($output) |
|
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246 | ->send_arg ("/bin/echo", "hi") |
|
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247 | ->run ("run", my $cv = AE::cv); |
88 | |
248 | |
89 | If you need some form of RPC, you can either implement it yourself |
249 | my $stderr = $cv->recv; |
90 | in whatever way you like, use some message-passing module such |
|
|
91 | as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use |
|
|
92 | L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages, |
|
|
93 | and so on. |
|
|
94 | |
|
|
95 | =head1 PROBLEM STATEMENT |
|
|
96 | |
|
|
97 | There are two ways to implement parallel processing on UNIX like operating |
|
|
98 | systems - fork and process, and fork+exec and process. They have different |
|
|
99 | advantages and disadvantages that I describe below, together with how this |
|
|
100 | module tries to mitigate the disadvantages. |
|
|
101 | |
|
|
102 | =over 4 |
|
|
103 | |
|
|
104 | =item Forking from a big process can be very slow (a 5GB process needs |
|
|
105 | 0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead |
|
|
106 | is often shared with exec (because you have to fork first), but in some |
|
|
107 | circumstances (e.g. when vfork is used), fork+exec can be much faster. |
|
|
108 | |
|
|
109 | This module can help here by telling a small(er) helper process to fork, |
|
|
110 | or fork+exec instead. |
|
|
111 | |
|
|
112 | =item Forking usually creates a copy-on-write copy of the parent |
|
|
113 | process. Memory (for example, modules or data files that have been |
|
|
114 | will not take additional memory). When exec'ing a new process, modules |
|
|
115 | and data files might need to be loaded again, at extra CPU and memory |
|
|
116 | cost. Likewise when forking, all data structures are copied as well - if |
|
|
117 | the program frees them and replaces them by new data, the child processes |
|
|
118 | will retain the memory even if it isn't used. |
|
|
119 | |
|
|
120 | This module allows the main program to do a controlled fork, and allows |
|
|
121 | modules to exec processes safely at any time. When creating a custom |
|
|
122 | process pool you can take advantage of data sharing via fork without |
|
|
123 | risking to share large dynamic data structures that will blow up child |
|
|
124 | memory usage. |
|
|
125 | |
|
|
126 | =item Exec'ing a new perl process might be difficult and slow. For |
|
|
127 | example, it is not easy to find the correct path to the perl interpreter, |
|
|
128 | and all modules have to be loaded from disk again. Long running processes |
|
|
129 | might run into problems when perl is upgraded for example. |
|
|
130 | |
|
|
131 | This module supports creating pre-initialised perl processes to be used |
|
|
132 | as template, and also tries hard to identify the correct path to the perl |
|
|
133 | interpreter. With a cooperative main program, exec'ing the interpreter |
|
|
134 | might not even be necessary. |
|
|
135 | |
|
|
136 | =item Forking might be impossible when a program is running. For example, |
|
|
137 | POSIX makes it almost impossible to fork from a multi-threaded program and |
|
|
138 | do anything useful in the child - strictly speaking, if your perl program |
|
|
139 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
|
|
140 | you cannot call fork on the perl level anymore, at all. |
|
|
141 | |
|
|
142 | This module can safely fork helper processes at any time, by calling |
|
|
143 | fork+exec in C, in a POSIX-compatible way. |
|
|
144 | |
|
|
145 | =item Parallel processing with fork might be inconvenient or difficult |
|
|
146 | to implement. For example, when a program uses an event loop and creates |
|
|
147 | watchers it becomes very hard to use the event loop from a child |
|
|
148 | program, as the watchers already exist but are only meaningful in the |
|
|
149 | parent. Worse, a module might want to use such a system, not knowing |
|
|
150 | whether another module or the main program also does, leading to problems. |
|
|
151 | |
|
|
152 | This module only lets the main program create pools by forking (because |
|
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153 | only the main program can know when it is still safe to do so) - all other |
|
|
154 | pools are created by fork+exec, after which such modules can again be |
|
|
155 | loaded. |
|
|
156 | |
|
|
157 | =back |
|
|
158 | |
250 | |
159 | =head1 CONCEPTS |
251 | =head1 CONCEPTS |
160 | |
252 | |
161 | This module can create new processes either by executing a new perl |
253 | This module can create new processes either by executing a new perl |
162 | process, or by forking from an existing "template" process. |
254 | process, or by forking from an existing "template" process. |
… | |
… | |
241 | my ($fork_fh) = @_; |
333 | my ($fork_fh) = @_; |
242 | }); |
334 | }); |
243 | |
335 | |
244 | =back |
336 | =back |
245 | |
337 | |
246 | =head1 FUNCTIONS |
338 | =head1 THE C<AnyEvent::Fork> CLASS |
|
|
339 | |
|
|
340 | This module exports nothing, and only implements a single class - |
|
|
341 | C<AnyEvent::Fork>. |
|
|
342 | |
|
|
343 | There are two class constructors that both create new processes - C<new> |
|
|
344 | and C<new_exec>. The C<fork> method creates a new process by forking an |
|
|
345 | existing one and could be considered a third constructor. |
|
|
346 | |
|
|
347 | Most of the remaining methods deal with preparing the new process, by |
|
|
348 | loading code, evaluating code and sending data to the new process. They |
|
|
349 | usually return the process object, so you can chain method calls. |
|
|
350 | |
|
|
351 | If a process object is destroyed before calling its C<run> method, then |
|
|
352 | the process simply exits. After C<run> is called, all responsibility is |
|
|
353 | passed to the specified function. |
|
|
354 | |
|
|
355 | As long as there is any outstanding work to be done, process objects |
|
|
356 | resist being destroyed, so there is no reason to store them unless you |
|
|
357 | need them later - configure and forget works just fine. |
247 | |
358 | |
248 | =over 4 |
359 | =over 4 |
249 | |
360 | |
250 | =cut |
361 | =cut |
251 | |
362 | |
… | |
… | |
261 | use IO::FDPass; |
372 | use IO::FDPass; |
262 | |
373 | |
263 | our $VERSION = 0.5; |
374 | our $VERSION = 0.5; |
264 | |
375 | |
265 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
376 | our $PERL; # the path to the perl interpreter, deduces with various forms of magic |
266 | |
|
|
267 | =item my $pool = new AnyEvent::Fork key => value... |
|
|
268 | |
|
|
269 | Create a new process pool. The following named parameters are supported: |
|
|
270 | |
377 | |
271 | =over 4 |
378 | =over 4 |
272 | |
379 | |
273 | =back |
380 | =back |
274 | |
381 | |
… | |
… | |
370 | Create a new "empty" perl interpreter process and returns its process |
477 | Create a new "empty" perl interpreter process and returns its process |
371 | object for further manipulation. |
478 | object for further manipulation. |
372 | |
479 | |
373 | The new process is forked from a template process that is kept around |
480 | The new process is forked from a template process that is kept around |
374 | for this purpose. When it doesn't exist yet, it is created by a call to |
481 | for this purpose. When it doesn't exist yet, it is created by a call to |
375 | C<new_exec> and kept around for future calls. |
482 | C<new_exec> first and then stays around for future calls. |
376 | |
|
|
377 | When the process object is destroyed, it will release the file handle |
|
|
378 | that connects it with the new process. When the new process has not yet |
|
|
379 | called C<run>, then the process will exit. Otherwise, what happens depends |
|
|
380 | entirely on the code that is executed. |
|
|
381 | |
483 | |
382 | =cut |
484 | =cut |
383 | |
485 | |
384 | sub new { |
486 | sub new { |
385 | my $class = shift; |
487 | my $class = shift; |
… | |
… | |
475 | } |
577 | } |
476 | |
578 | |
477 | =item $pid = $proc->pid |
579 | =item $pid = $proc->pid |
478 | |
580 | |
479 | Returns the process id of the process I<iff it is a direct child of the |
581 | Returns the process id of the process I<iff it is a direct child of the |
480 | process> running AnyEvent::Fork, and C<undef> otherwise. |
582 | process running AnyEvent::Fork>, and C<undef> otherwise. |
481 | |
583 | |
482 | Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and |
584 | Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and |
483 | L<AnyEvent::Fork::Template> are direct children, and you are responsible |
585 | L<AnyEvent::Fork::Template> are direct children, and you are responsible |
484 | to clean up their zombies when they die. |
586 | to clean up their zombies when they die. |
485 | |
587 | |
486 | All other processes are not direct children, and will be cleaned up by |
588 | All other processes are not direct children, and will be cleaned up by |
487 | AnyEvent::Fork. |
589 | AnyEvent::Fork itself. |
488 | |
590 | |
489 | =cut |
591 | =cut |
490 | |
592 | |
491 | sub pid { |
593 | sub pid { |
492 | $_[0][0] |
594 | $_[0][0] |
493 | } |
595 | } |
494 | |
596 | |
495 | =item $proc = $proc->eval ($perlcode, @args) |
597 | =item $proc = $proc->eval ($perlcode, @args) |
496 | |
598 | |
497 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
599 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
498 | the strings specified by C<@args>. |
600 | the strings specified by C<@args>, in the "main" package. |
499 | |
601 | |
500 | This call is meant to do any custom initialisation that might be required |
602 | This call is meant to do any custom initialisation that might be required |
501 | (for example, the C<require> method uses it). It's not supposed to be used |
603 | (for example, the C<require> method uses it). It's not supposed to be used |
502 | to completely take over the process, use C<run> for that. |
604 | to completely take over the process, use C<run> for that. |
503 | |
605 | |
504 | The code will usually be executed after this call returns, and there is no |
606 | The code will usually be executed after this call returns, and there is no |
505 | way to pass anything back to the calling process. Any evaluation errors |
607 | way to pass anything back to the calling process. Any evaluation errors |
506 | will be reported to stderr and cause the process to exit. |
608 | will be reported to stderr and cause the process to exit. |
507 | |
609 | |
|
|
610 | If you want to execute some code (that isn't in a module) to take over the |
|
|
611 | process, you should compile a function via C<eval> first, and then call |
|
|
612 | it via C<run>. This also gives you access to any arguments passed via the |
|
|
613 | C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as |
|
|
614 | a faster fork+exec> example to see it in action. |
|
|
615 | |
508 | Returns the process object for easy chaining of method calls. |
616 | Returns the process object for easy chaining of method calls. |
509 | |
617 | |
510 | =cut |
618 | =cut |
511 | |
619 | |
512 | sub eval { |
620 | sub eval { |
… | |
… | |
537 | =item $proc = $proc->send_fh ($handle, ...) |
645 | =item $proc = $proc->send_fh ($handle, ...) |
538 | |
646 | |
539 | Send one or more file handles (I<not> file descriptors) to the process, |
647 | Send one or more file handles (I<not> file descriptors) to the process, |
540 | to prepare a call to C<run>. |
648 | to prepare a call to C<run>. |
541 | |
649 | |
542 | The process object keeps a reference to the handles until this is done, |
650 | The process object keeps a reference to the handles until they have |
543 | so you must not explicitly close the handles. This is most easily |
651 | been passed over to the process, so you must not explicitly close the |
544 | accomplished by simply not storing the file handles anywhere after passing |
652 | handles. This is most easily accomplished by simply not storing the file |
545 | them to this method. |
653 | handles anywhere after passing them to this method - when AnyEvent::Fork |
|
|
654 | is finished using them, perl will automatically close them. |
546 | |
655 | |
547 | Returns the process object for easy chaining of method calls. |
656 | Returns the process object for easy chaining of method calls. |
548 | |
657 | |
549 | Example: pass a file handle to a process, and release it without |
658 | Example: pass a file handle to a process, and release it without |
550 | closing. It will be closed automatically when it is no longer used. |
659 | closing. It will be closed automatically when it is no longer used. |
… | |
… | |
566 | } |
675 | } |
567 | |
676 | |
568 | =item $proc = $proc->send_arg ($string, ...) |
677 | =item $proc = $proc->send_arg ($string, ...) |
569 | |
678 | |
570 | Send one or more argument strings to the process, to prepare a call to |
679 | Send one or more argument strings to the process, to prepare a call to |
571 | C<run>. The strings can be any octet string. |
680 | C<run>. The strings can be any octet strings. |
572 | |
681 | |
573 | The protocol is optimised to pass a moderate number of relatively short |
682 | The protocol is optimised to pass a moderate number of relatively short |
574 | strings - while you can pass up to 4GB of data in one go, this is more |
683 | strings - while you can pass up to 4GB of data in one go, this is more |
575 | meant to pass some ID information or other startup info, not big chunks of |
684 | meant to pass some ID information or other startup info, not big chunks of |
576 | data. |
685 | data. |
… | |
… | |
587 | $self |
696 | $self |
588 | } |
697 | } |
589 | |
698 | |
590 | =item $proc->run ($func, $cb->($fh)) |
699 | =item $proc->run ($func, $cb->($fh)) |
591 | |
700 | |
592 | Enter the function specified by the fully qualified name in C<$func> in |
701 | Enter the function specified by the function name in C<$func> in the |
593 | the process. The function is called with the communication socket as first |
702 | process. The function is called with the communication socket as first |
594 | argument, followed by all file handles and string arguments sent earlier |
703 | argument, followed by all file handles and string arguments sent earlier |
595 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
704 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
596 | |
705 | |
597 | If the called function returns, the process exits. |
|
|
598 | |
|
|
599 | Preparing the process can take time - when the process is ready, the |
|
|
600 | callback is invoked with the local communications socket as argument. |
|
|
601 | |
|
|
602 | The process object becomes unusable on return from this function. |
706 | The process object becomes unusable on return from this function - any |
|
|
707 | further method calls result in undefined behaviour. |
|
|
708 | |
|
|
709 | The function name should be fully qualified, but if it isn't, it will be |
|
|
710 | looked up in the C<main> package. |
|
|
711 | |
|
|
712 | If the called function returns, doesn't exist, or any error occurs, the |
|
|
713 | process exits. |
|
|
714 | |
|
|
715 | Preparing the process is done in the background - when all commands have |
|
|
716 | been sent, the callback is invoked with the local communications socket |
|
|
717 | as argument. At this point you can start using the socket in any way you |
|
|
718 | like. |
603 | |
719 | |
604 | If the communication socket isn't used, it should be closed on both sides, |
720 | If the communication socket isn't used, it should be closed on both sides, |
605 | to save on kernel memory. |
721 | to save on kernel memory. |
606 | |
722 | |
607 | The socket is non-blocking in the parent, and blocking in the newly |
723 | The socket is non-blocking in the parent, and blocking in the newly |
608 | created process. The close-on-exec flag is set on both. Even if not used |
724 | created process. The close-on-exec flag is set in both. |
|
|
725 | |
609 | otherwise, the socket can be a good indicator for the existence of the |
726 | Even if not used otherwise, the socket can be a good indicator for the |
610 | process - if the other process exits, you get a readable event on it, |
727 | existence of the process - if the other process exits, you get a readable |
611 | because exiting the process closes the socket (if it didn't create any |
728 | event on it, because exiting the process closes the socket (if it didn't |
612 | children using fork). |
729 | create any children using fork). |
613 | |
730 | |
614 | Example: create a template for a process pool, pass a few strings, some |
731 | Example: create a template for a process pool, pass a few strings, some |
615 | file handles, then fork, pass one more string, and run some code. |
732 | file handles, then fork, pass one more string, and run some code. |
616 | |
733 | |
617 | my $pool = AnyEvent::Fork |
734 | my $pool = AnyEvent::Fork |
… | |
… | |
625 | ->send_arg ("str3") |
742 | ->send_arg ("str3") |
626 | ->run ("Some::function", sub { |
743 | ->run ("Some::function", sub { |
627 | my ($fh) = @_; |
744 | my ($fh) = @_; |
628 | |
745 | |
629 | # fh is nonblocking, but we trust that the OS can accept these |
746 | # fh is nonblocking, but we trust that the OS can accept these |
630 | # extra 3 octets anyway. |
747 | # few octets anyway. |
631 | syswrite $fh, "hi #$_\n"; |
748 | syswrite $fh, "hi #$_\n"; |
632 | |
749 | |
633 | # $fh is being closed here, as we don't store it anywhere |
750 | # $fh is being closed here, as we don't store it anywhere |
634 | }); |
751 | }); |
635 | } |
752 | } |
… | |
… | |
637 | # Some::function might look like this - all parameters passed before fork |
754 | # Some::function might look like this - all parameters passed before fork |
638 | # and after will be passed, in order, after the communications socket. |
755 | # and after will be passed, in order, after the communications socket. |
639 | sub Some::function { |
756 | sub Some::function { |
640 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
757 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
641 | |
758 | |
642 | print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" |
759 | print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order |
643 | } |
760 | } |
644 | |
761 | |
645 | =cut |
762 | =cut |
646 | |
763 | |
647 | sub run { |
764 | sub run { |
… | |
… | |
681 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
798 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
682 | |
799 | |
683 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
800 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
684 | though it uses the same operations, but adds a lot of overhead? |
801 | though it uses the same operations, but adds a lot of overhead? |
685 | |
802 | |
686 | The difference is simply the process size: forking the 6MB process takes |
803 | The difference is simply the process size: forking the 5MB process takes |
687 | so much longer than forking the 2.5MB template process that the overhead |
804 | so much longer than forking the 2.5MB template process that the extra |
688 | introduced is canceled out. |
805 | overhead introduced is canceled out. |
689 | |
806 | |
690 | If the benchmark process grows, the normal fork becomes even slower: |
807 | If the benchmark process grows, the normal fork becomes even slower: |
691 | |
808 | |
692 | 1340 new processes, manual fork in a 20MB process |
809 | 1340 new processes, manual fork of a 20MB process |
693 | 731 new processes, manual fork in a 200MB process |
810 | 731 new processes, manual fork of a 200MB process |
694 | 235 new processes, manual fork in a 2000MB process |
811 | 235 new processes, manual fork of a 2000MB process |
695 | |
812 | |
696 | What that means (to me) is that I can use this module without having a |
813 | What that means (to me) is that I can use this module without having a bad |
697 | very bad conscience because of the extra overhead required to start new |
814 | conscience because of the extra overhead required to start new processes. |
698 | processes. |
|
|
699 | |
815 | |
700 | =head1 TYPICAL PROBLEMS |
816 | =head1 TYPICAL PROBLEMS |
701 | |
817 | |
702 | This section lists typical problems that remain. I hope by recognising |
818 | This section lists typical problems that remain. I hope by recognising |
703 | them, most can be avoided. |
819 | them, most can be avoided. |
704 | |
820 | |
705 | =over 4 |
821 | =over 4 |
706 | |
822 | |
707 | =item "leaked" file descriptors for exec'ed processes |
823 | =item leaked file descriptors for exec'ed processes |
708 | |
824 | |
709 | POSIX systems inherit file descriptors by default when exec'ing a new |
825 | POSIX systems inherit file descriptors by default when exec'ing a new |
710 | process. While perl itself laudably sets the close-on-exec flags on new |
826 | process. While perl itself laudably sets the close-on-exec flags on new |
711 | file handles, most C libraries don't care, and even if all cared, it's |
827 | file handles, most C libraries don't care, and even if all cared, it's |
712 | often not possible to set the flag in a race-free manner. |
828 | often not possible to set the flag in a race-free manner. |
… | |
… | |
732 | libraries or the code that leaks those file descriptors. |
848 | libraries or the code that leaks those file descriptors. |
733 | |
849 | |
734 | Fortunately, most of these leaked descriptors do no harm, other than |
850 | Fortunately, most of these leaked descriptors do no harm, other than |
735 | sitting on some resources. |
851 | sitting on some resources. |
736 | |
852 | |
737 | =item "leaked" file descriptors for fork'ed processes |
853 | =item leaked file descriptors for fork'ed processes |
738 | |
854 | |
739 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
855 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
740 | which closes file descriptors not marked for being inherited. |
856 | which closes file descriptors not marked for being inherited. |
741 | |
857 | |
742 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
858 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
… | |
… | |
751 | |
867 | |
752 | The solution is to either not load these modules before use'ing |
868 | The solution is to either not load these modules before use'ing |
753 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
869 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
754 | initialising them, for example, by calling C<init Gtk2> manually. |
870 | initialising them, for example, by calling C<init Gtk2> manually. |
755 | |
871 | |
756 | =item exit runs destructors |
872 | =item exiting calls object destructors |
757 | |
873 | |
758 | This only applies to users of Lc<AnyEvent::Fork:Early> and |
874 | This only applies to users of L<AnyEvent::Fork:Early> and |
759 | L<AnyEvent::Fork::Template>. |
875 | L<AnyEvent::Fork::Template>, or when initialiasing code creates objects |
|
|
876 | that reference external resources. |
760 | |
877 | |
761 | When a process created by AnyEvent::Fork exits, it might do so by calling |
878 | When a process created by AnyEvent::Fork exits, it might do so by calling |
762 | exit, or simply letting perl reach the end of the program. At which point |
879 | exit, or simply letting perl reach the end of the program. At which point |
763 | Perl runs all destructors. |
880 | Perl runs all destructors. |
764 | |
881 | |
… | |
… | |
783 | to make it so, mostly due to the bloody broken perl that nobody seems to |
900 | to make it so, mostly due to the bloody broken perl that nobody seems to |
784 | care about. The fork emulation is a bad joke - I have yet to see something |
901 | care about. The fork emulation is a bad joke - I have yet to see something |
785 | useful that you can do with it without running into memory corruption |
902 | useful that you can do with it without running into memory corruption |
786 | issues or other braindamage. Hrrrr. |
903 | issues or other braindamage. Hrrrr. |
787 | |
904 | |
788 | Cygwin perl is not supported at the moment, as it should implement fd |
905 | Cygwin perl is not supported at the moment due to some hilarious |
789 | passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
906 | shortcomings of its API - see L<IO::FDPoll> for more details. |
790 | support enough functionality to do it. |
|
|
791 | |
907 | |
792 | =head1 SEE ALSO |
908 | =head1 SEE ALSO |
793 | |
909 | |
794 | L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
910 | L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
795 | L<AnyEvent::Fork::Template> (to create a process by forking the main |
911 | L<AnyEvent::Fork::Template> (to create a process by forking the main |