1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
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 | ATTENTION, this is a very early release, and very untested. Consider it a |
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6 | technology preview. |
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7 | |
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8 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
9 | |
6 | |
10 | use AnyEvent::Fork; |
7 | use AnyEvent::Fork; |
11 | |
8 | |
12 | ################################################################## |
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 |
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23 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
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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 | =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 | |
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45 | =head1 PROBLEM STATEMENT |
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46 | |
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47 | There are two traditional ways to implement parallel processing on UNIX |
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48 | like operating systems - fork and process, and fork+exec and process. They |
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49 | have different advantages and disadvantages that I describe below, |
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50 | together with how this module tries to mitigate the disadvantages. |
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51 | |
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52 | =over 4 |
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53 | |
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54 | =item Forking from a big process can be very slow. |
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55 | |
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56 | A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This |
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57 | overhead is often shared with exec (because you have to fork first), but |
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58 | in some circumstances (e.g. when vfork is used), fork+exec can be much |
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59 | faster. |
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60 | |
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61 | This module can help here by telling a small(er) helper process to fork, |
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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. |
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64 | |
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65 | =item Forking usually creates a copy-on-write copy of the parent |
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66 | process. |
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67 | |
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68 | For example, modules or data files that are loaded will not use additional |
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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 |
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72 | them and replaces them by new data, the child processes will retain the |
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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. |
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78 | |
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79 | This module allows the main program to do a controlled fork, and allows |
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80 | modules to exec processes safely at any time. When creating a custom |
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81 | process pool you can take advantage of data sharing via fork without |
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82 | risking to share large dynamic data structures that will blow up child |
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83 | memory usage. |
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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 | |
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88 | =item Exec'ing a new perl process might be difficult. |
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89 | |
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90 | For example, it is not easy to find the correct path to the perl |
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91 | interpreter - C<$^X> might not be a perl interpreter at all. |
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92 | |
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93 | This module tries hard to identify the correct path to the perl |
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94 | interpreter. With a cooperative main program, exec'ing the interpreter |
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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. |
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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 | |
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109 | =item Forking might be impossible when a program is running. |
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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 | |
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118 | This module can safely fork helper processes at any time, by calling |
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119 | fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>). |
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120 | |
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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 | |
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124 | For example, when a program uses an event loop and creates watchers it |
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125 | becomes very hard to use the event loop from a child program, as the |
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126 | watchers already exist but are only meaningful in the parent. Worse, a |
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127 | module might want to use such a module, not knowing whether another module |
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128 | or the main program also does, leading to problems. |
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129 | |
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130 | Apart from event loops, graphical toolkits also commonly fall into the |
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131 | "unsafe module" category, or just about anything that communicates with |
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132 | the external world, such as network libraries and file I/O modules, which |
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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. |
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140 | |
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141 | =back |
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142 | |
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143 | =head1 EXAMPLES |
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144 | |
13 | # create a single new process, tell it to run your worker function |
145 | =head2 Create a single new process, tell it to run your worker function. |
14 | |
146 | |
15 | AnyEvent::Fork |
147 | AnyEvent::Fork |
16 | ->new |
148 | ->new |
17 | ->require ("MyModule") |
149 | ->require ("MyModule") |
18 | ->run ("MyModule::worker, sub { |
150 | ->run ("MyModule::worker, sub { |
… | |
… | |
20 | |
152 | |
21 | # now $master_filehandle is connected to the |
153 | # now $master_filehandle is connected to the |
22 | # $slave_filehandle in the new process. |
154 | # $slave_filehandle in the new process. |
23 | }); |
155 | }); |
24 | |
156 | |
25 | # MyModule::worker might look like this |
157 | MyModule might look like this: |
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158 | |
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159 | package MyModule; |
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160 | |
26 | sub MyModule::worker { |
161 | sub worker { |
27 | my ($slave_filehandle) = @_; |
162 | my ($slave_filehandle) = @_; |
28 | |
163 | |
29 | # now $slave_filehandle is connected to the $master_filehandle |
164 | # now $slave_filehandle is connected to the $master_filehandle |
30 | # in the original prorcess. have fun! |
165 | # in the original prorcess. have fun! |
31 | } |
166 | } |
32 | |
167 | |
33 | ################################################################## |
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34 | # create a pool of server processes all accepting on the same socket |
168 | =head2 Create a pool of server processes all accepting on the same socket. |
35 | |
169 | |
36 | # create listener socket |
170 | # create listener socket |
37 | my $listener = ...; |
171 | my $listener = ...; |
38 | |
172 | |
39 | # create a pool template, initialise it and give it the socket |
173 | # create a pool template, initialise it and give it the socket |
… | |
… | |
51 | } |
185 | } |
52 | |
186 | |
53 | # now do other things - maybe use the filehandle provided by run |
187 | # now do other things - maybe use the filehandle provided by run |
54 | # to wait for the processes to die. or whatever. |
188 | # to wait for the processes to die. or whatever. |
55 | |
189 | |
56 | # My::Server::run might look like this |
190 | My::Server might look like this: |
57 | sub My::Server::run { |
191 | |
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192 | package My::Server; |
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193 | |
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194 | sub run { |
58 | my ($slave, $listener, $id) = @_; |
195 | my ($slave, $listener, $id) = @_; |
59 | |
196 | |
60 | close $slave; # we do not use the socket, so close it to save resources |
197 | close $slave; # we do not use the socket, so close it to save resources |
61 | |
198 | |
62 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
199 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
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64 | while (my $socket = $listener->accept) { |
201 | while (my $socket = $listener->accept) { |
65 | # do sth. with new socket |
202 | # do sth. with new socket |
66 | } |
203 | } |
67 | } |
204 | } |
68 | |
205 | |
69 | =head1 DESCRIPTION |
206 | =head2 use AnyEvent::Fork as a faster fork+exec |
70 | |
207 | |
71 | This module allows you to create new processes, without actually forking |
208 | This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to |
72 | them from your current process (avoiding the problems of forking), but |
209 | the communications socket. It is usually faster than fork+exec, but still |
73 | preserving most of the advantages of fork. |
210 | let's you prepare the environment. |
74 | |
211 | |
75 | It can be used to create new worker processes or new independent |
212 | open my $output, ">/tmp/log" or die "$!"; |
76 | subprocesses for short- and long-running jobs, process pools (e.g. for use |
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77 | in pre-forked servers) but also to spawn new external processes (such as |
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78 | CGI scripts from a webserver), which can be faster (and more well behaved) |
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79 | than using fork+exec in big processes. |
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80 | |
213 | |
81 | Special care has been taken to make this module useful from other modules, |
214 | AnyEvent::Fork |
82 | while still supporting specialised environments such as L<App::Staticperl> |
215 | ->new |
83 | or L<PAR::Packer>. |
216 | ->eval (' |
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217 | sub run { |
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218 | my ($fh, $output, @cmd) = @_; |
84 | |
219 | |
85 | =head1 PROBLEM STATEMENT |
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, ">&", $fh or die; |
86 | |
223 | |
87 | There are two ways to implement parallel processing on UNIX like operating |
224 | exec @cmd; |
88 | systems - fork and process, and fork+exec and process. They have different |
225 | } |
89 | advantages and disadvantages that I describe below, together with how this |
226 | ') |
90 | module tries to mitigate the disadvantages. |
227 | ->send_fh ($output) |
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228 | ->send_arg ("/bin/echo", "hi") |
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229 | ->run ("run", my $cv = AE::cv); |
91 | |
230 | |
92 | =over 4 |
231 | my $stderr = $cv->recv; |
93 | |
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94 | =item Forking from a big process can be very slow (a 5GB process needs |
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95 | 0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead |
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96 | is often shared with exec (because you have to fork first), but in some |
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97 | circumstances (e.g. when vfork is used), fork+exec can be much faster. |
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98 | |
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99 | This module can help here by telling a small(er) helper process to fork, |
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100 | or fork+exec instead. |
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101 | |
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102 | =item Forking usually creates a copy-on-write copy of the parent |
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103 | process. Memory (for example, modules or data files that have been |
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104 | will not take additional memory). When exec'ing a new process, modules |
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105 | and data files might need to be loaded again, at extra cpu and memory |
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106 | cost. Likewise when forking, all data structures are copied as well - if |
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107 | the program frees them and replaces them by new data, the child processes |
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108 | will retain the memory even if it isn't used. |
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109 | |
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110 | This module allows the main program to do a controlled fork, and allows |
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111 | modules to exec processes safely at any time. When creating a custom |
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112 | process pool you can take advantage of data sharing via fork without |
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113 | risking to share large dynamic data structures that will blow up child |
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114 | memory usage. |
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115 | |
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116 | =item Exec'ing a new perl process might be difficult and slow. For |
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117 | example, it is not easy to find the correct path to the perl interpreter, |
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118 | and all modules have to be loaded from disk again. Long running processes |
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119 | might run into problems when perl is upgraded for example. |
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120 | |
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121 | This module supports creating pre-initialised perl processes to be used |
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122 | as template, and also tries hard to identify the correct path to the perl |
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123 | interpreter. With a cooperative main program, exec'ing the interpreter |
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124 | might not even be necessary. |
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125 | |
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126 | =item Forking might be impossible when a program is running. For example, |
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127 | POSIX makes it almost impossible to fork from a multithreaded program and |
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128 | do anything useful in the child - strictly speaking, if your perl program |
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129 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
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130 | you cannot call fork on the perl level anymore, at all. |
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131 | |
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132 | This module can safely fork helper processes at any time, by caling |
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133 | fork+exec in C, in a POSIX-compatible way. |
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134 | |
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135 | =item Parallel processing with fork might be inconvenient or difficult |
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136 | to implement. For example, when a program uses an event loop and creates |
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137 | watchers it becomes very hard to use the event loop from a child |
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138 | program, as the watchers already exist but are only meaningful in the |
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139 | parent. Worse, a module might want to use such a system, not knowing |
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140 | whether another module or the main program also does, leading to problems. |
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141 | |
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142 | This module only lets the main program create pools by forking (because |
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143 | only the main program can know when it is still safe to do so) - all other |
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144 | pools are created by fork+exec, after which such modules can again be |
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145 | loaded. |
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146 | |
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147 | =back |
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148 | |
232 | |
149 | =head1 CONCEPTS |
233 | =head1 CONCEPTS |
150 | |
234 | |
151 | 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 |
152 | process, or by forking from an existing "template" process. |
236 | process, or by forking from an existing "template" process. |
… | |
… | |
169 | 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 |
170 | 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 |
171 | time, and the memory is not shared with anything else. |
255 | time, and the memory is not shared with anything else. |
172 | |
256 | |
173 | 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 |
174 | option of starting and stipping it on demand. |
258 | option of starting and stopping it on demand. |
175 | |
259 | |
176 | Example: |
260 | Example: |
177 | |
261 | |
178 | AnyEvent::Fork |
262 | AnyEvent::Fork |
179 | ->new |
263 | ->new |
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194 | 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 |
195 | consumes relatively little memory of its own. |
279 | consumes relatively little memory of its own. |
196 | |
280 | |
197 | 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 |
198 | 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 |
199 | 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 |
200 | the template process. |
284 | the template process. |
201 | |
285 | |
202 | Example: |
286 | Example: |
203 | |
287 | |
204 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
288 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
… | |
… | |
231 | my ($fork_fh) = @_; |
315 | my ($fork_fh) = @_; |
232 | }); |
316 | }); |
233 | |
317 | |
234 | =back |
318 | =back |
235 | |
319 | |
236 | =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. |
237 | |
340 | |
238 | =over 4 |
341 | =over 4 |
239 | |
342 | |
240 | =cut |
343 | =cut |
241 | |
344 | |
242 | package AnyEvent::Fork; |
345 | package AnyEvent::Fork; |
243 | |
346 | |
244 | use common::sense; |
347 | use common::sense; |
245 | |
348 | |
246 | use Socket (); |
349 | use Errno (); |
247 | |
350 | |
248 | use AnyEvent; |
351 | use AnyEvent; |
249 | use AnyEvent::Fork::Util; |
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250 | use AnyEvent::Util (); |
352 | use AnyEvent::Util (); |
251 | |
353 | |
252 | our $VERSION = $AnyEvent::Fork::Util::VERSION; |
354 | use IO::FDPass; |
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355 | |
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356 | our $VERSION = 0.5; |
253 | |
357 | |
254 | 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 |
255 | |
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256 | =item my $pool = new AnyEvent::Fork key => value... |
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257 | |
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258 | Create a new process pool. The following named parameters are supported: |
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259 | |
359 | |
260 | =over 4 |
360 | =over 4 |
261 | |
361 | |
262 | =back |
362 | =back |
263 | |
363 | |
… | |
… | |
270 | our $TEMPLATE; |
370 | our $TEMPLATE; |
271 | |
371 | |
272 | sub _cmd { |
372 | sub _cmd { |
273 | my $self = shift; |
373 | my $self = shift; |
274 | |
374 | |
275 | #TODO: maybe append the packet to any existing string command already in the queue |
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276 | |
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277 | # 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 |
278 | # 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 |
279 | 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]; |
280 | |
379 | |
281 | $self->[3] ||= AE::io $self->[1], 1, sub { |
380 | $self->[3] ||= AE::io $self->[1], 1, sub { |
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381 | do { |
282 | # send the next "thing" in the queue - either a reference to an fh, |
382 | # send the next "thing" in the queue - either a reference to an fh, |
283 | # or a plain string. |
383 | # or a plain string. |
284 | |
384 | |
285 | if (ref $self->[2][0]) { |
385 | if (ref $self->[2][0]) { |
286 | # send fh |
386 | # send fh |
287 | AnyEvent::Fork::Util::fd_send fileno $self->[1], fileno ${ $self->[2][0] } |
387 | unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) { |
|
|
388 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
|
|
389 | undef $self->[3]; |
|
|
390 | die "AnyEvent::Fork: file descriptor send failure: $!"; |
|
|
391 | } |
|
|
392 | |
288 | and shift @{ $self->[2] }; |
393 | shift @{ $self->[2] }; |
289 | |
394 | |
290 | } else { |
395 | } else { |
291 | # send string |
396 | # send string |
292 | 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]; |
293 | or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" }; |
402 | die "AnyEvent::Fork: command write failure: $!"; |
|
|
403 | } |
294 | |
404 | |
295 | substr $self->[2][0], 0, $len, ""; |
405 | substr $self->[2][0], 0, $len, ""; |
296 | shift @{ $self->[2] } unless length $self->[2][0]; |
406 | shift @{ $self->[2] } unless length $self->[2][0]; |
297 | } |
407 | } |
|
|
408 | } while @{ $self->[2] }; |
298 | |
409 | |
299 | unless (@{ $self->[2] }) { |
410 | # everything written |
300 | undef $self->[3]; |
411 | undef $self->[3]; |
|
|
412 | |
301 | # invoke run callback |
413 | # invoke run callback, if any |
302 | $self->[0]->($self->[1]) if $self->[0]; |
414 | $self->[4]->($self->[1]) if $self->[4]; |
303 | } |
|
|
304 | }; |
415 | }; |
|
|
416 | |
|
|
417 | () # make sure we don't leak the watcher |
305 | } |
418 | } |
306 | |
419 | |
307 | sub _new { |
420 | sub _new { |
308 | my ($self, $fh) = @_; |
421 | my ($self, $fh, $pid) = @_; |
309 | |
422 | |
310 | AnyEvent::Util::fh_nonblocking $fh, 1; |
423 | AnyEvent::Util::fh_nonblocking $fh, 1; |
311 | |
424 | |
312 | $self = bless [ |
425 | $self = bless [ |
313 | undef, # run callback |
426 | $pid, |
314 | $fh, |
427 | $fh, |
315 | [], # write queue - strings or fd's |
428 | [], # write queue - strings or fd's |
316 | undef, # AE watcher |
429 | undef, # AE watcher |
317 | ], $self; |
430 | ], $self; |
318 | |
431 | |
… | |
… | |
329 | if ($pid eq 0) { |
442 | if ($pid eq 0) { |
330 | require AnyEvent::Fork::Serve; |
443 | require AnyEvent::Fork::Serve; |
331 | $AnyEvent::Fork::Serve::OWNER = $parent; |
444 | $AnyEvent::Fork::Serve::OWNER = $parent; |
332 | close $fh; |
445 | close $fh; |
333 | $0 = "$_[1] of $parent"; |
446 | $0 = "$_[1] of $parent"; |
|
|
447 | $SIG{CHLD} = 'IGNORE'; |
334 | AnyEvent::Fork::Serve::serve ($slave); |
448 | AnyEvent::Fork::Serve::serve ($slave); |
335 | AnyEvent::Fork::Util::_exit 0; |
449 | exit 0; |
336 | } elsif (!$pid) { |
450 | } elsif (!$pid) { |
337 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
451 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
338 | } |
452 | } |
339 | |
453 | |
340 | AnyEvent::Fork->_new ($fh) |
454 | AnyEvent::Fork->_new ($fh, $pid) |
341 | } |
455 | } |
342 | |
456 | |
343 | =item my $proc = new AnyEvent::Fork |
457 | =item my $proc = new AnyEvent::Fork |
344 | |
458 | |
345 | Create a new "empty" perl interpreter process and returns its process |
459 | Create a new "empty" perl interpreter process and returns its process |
346 | object for further manipulation. |
460 | object for further manipulation. |
347 | |
461 | |
348 | 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 |
349 | 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 |
350 | C<new_exec> and kept around for future calls. |
464 | C<new_exec> first and then stays around for future calls. |
351 | |
|
|
352 | When the process object is destroyed, it will release the file handle |
|
|
353 | that connects it with the new process. When the new process has not yet |
|
|
354 | called C<run>, then the process will exit. Otherwise, what happens depends |
|
|
355 | entirely on the code that is executed. |
|
|
356 | |
465 | |
357 | =cut |
466 | =cut |
358 | |
467 | |
359 | sub new { |
468 | sub new { |
360 | my $class = shift; |
469 | my $class = shift; |
… | |
… | |
396 | reduces the amount of memory sharing that is possible, and is also slower. |
505 | reduces the amount of memory sharing that is possible, and is also slower. |
397 | |
506 | |
398 | You should use C<new> whenever possible, except when having a template |
507 | You should use C<new> whenever possible, except when having a template |
399 | process around is unacceptable. |
508 | process around is unacceptable. |
400 | |
509 | |
401 | The path to the perl interpreter is divined usign various methods - first |
510 | The path to the perl interpreter is divined using various methods - first |
402 | C<$^X> is investigated to see if the path ends with something that sounds |
511 | C<$^X> is investigated to see if the path ends with something that sounds |
403 | as if it were the perl interpreter. Failing this, the module falls back to |
512 | as if it were the perl interpreter. Failing this, the module falls back to |
404 | using C<$Config::Config{perlpath}>. |
513 | using C<$Config::Config{perlpath}>. |
405 | |
514 | |
406 | =cut |
515 | =cut |
… | |
… | |
415 | my $perl = $; |
524 | my $perl = $; |
416 | |
525 | |
417 | # 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. |
418 | # 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 |
419 | unless ( |
528 | unless ( |
420 | (AnyEvent::Fork::Util::WIN32 || $perl =~ m%^/%) |
529 | ($^O eq "MSWin32" || $perl =~ m%^/%) |
421 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
530 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
422 | ) { |
531 | ) { |
423 | # if it doesn't look perlish enough, try Config |
532 | # if it doesn't look perlish enough, try Config |
424 | require Config; |
533 | require Config; |
425 | $perl = $Config::Config{perlpath}; |
534 | $perl = $Config::Config{perlpath}; |
… | |
… | |
436 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
545 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
437 | |
546 | |
438 | # 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 |
439 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
548 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
440 | my %env = %ENV; |
549 | my %env = %ENV; |
441 | $env{PERL5LIB} = join +(AnyEvent::Fork::Util::WIN32 ? ";" : ":"), grep !ref, @INC; |
550 | $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; |
442 | |
551 | |
443 | Proc::FastSpawn::spawn ( |
552 | my $pid = Proc::FastSpawn::spawn ( |
444 | $perl, |
553 | $perl, |
445 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
554 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
446 | [map "$_=$env{$_}", keys %env], |
555 | [map "$_=$env{$_}", keys %env], |
447 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
556 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
448 | |
557 | |
449 | $self->_new ($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] |
450 | } |
577 | } |
451 | |
578 | |
452 | =item $proc = $proc->eval ($perlcode, @args) |
579 | =item $proc = $proc->eval ($perlcode, @args) |
453 | |
580 | |
454 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
581 | Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to |
455 | the strings specified by C<@args>. |
582 | the strings specified by C<@args>, in the "main" package. |
456 | |
583 | |
457 | This call is meant to do any custom initialisation that might be required |
584 | This call is meant to do any custom initialisation that might be required |
458 | (for example, the C<require> method uses it). It's not supposed to be used |
585 | (for example, the C<require> method uses it). It's not supposed to be used |
459 | to completely take over the process, use C<run> for that. |
586 | to completely take over the process, use C<run> for that. |
460 | |
587 | |
461 | The code will usually be executed after this call returns, and there is no |
588 | The code will usually be executed after this call returns, and there is no |
462 | way to pass anything back to the calling process. Any evaluation errors |
589 | way to pass anything back to the calling process. Any evaluation errors |
463 | will be reported to stderr and cause the process to exit. |
590 | will be reported to stderr and cause the process to exit. |
464 | |
591 | |
|
|
592 | If you want to execute some code to take over the process (see the |
|
|
593 | "fork+exec" example in the SYNOPSIS), you should compile a function via |
|
|
594 | C<eval> first, and then call it via C<run>. This also gives you access to |
|
|
595 | any arguments passed via the C<send_xxx> methods, such as file handles. |
|
|
596 | |
465 | Returns the process object for easy chaining of method calls. |
597 | Returns the process object for easy chaining of method calls. |
466 | |
598 | |
467 | =cut |
599 | =cut |
468 | |
600 | |
469 | sub eval { |
601 | sub eval { |
470 | my ($self, $code, @args) = @_; |
602 | my ($self, $code, @args) = @_; |
471 | |
603 | |
472 | $self->_cmd (e => $code, @args); |
604 | $self->_cmd (e => pack "(w/a*)*", $code, @args); |
473 | |
605 | |
474 | $self |
606 | $self |
475 | } |
607 | } |
476 | |
608 | |
477 | =item $proc = $proc->require ($module, ...) |
609 | =item $proc = $proc->require ($module, ...) |
… | |
… | |
501 | accomplished by simply not storing the file handles anywhere after passing |
633 | accomplished by simply not storing the file handles anywhere after passing |
502 | them to this method. |
634 | them to this method. |
503 | |
635 | |
504 | Returns the process object for easy chaining of method calls. |
636 | Returns the process object for easy chaining of method calls. |
505 | |
637 | |
506 | Example: pass an fh to a process, and release it without closing. it will |
638 | Example: pass a file handle to a process, and release it without |
507 | be closed automatically when it is no longer used. |
639 | closing. It will be closed automatically when it is no longer used. |
508 | |
640 | |
509 | $proc->send_fh ($my_fh); |
641 | $proc->send_fh ($my_fh); |
510 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
642 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
511 | |
643 | |
512 | =cut |
644 | =cut |
… | |
… | |
525 | =item $proc = $proc->send_arg ($string, ...) |
657 | =item $proc = $proc->send_arg ($string, ...) |
526 | |
658 | |
527 | Send one or more argument strings to the process, to prepare a call to |
659 | Send one or more argument strings to the process, to prepare a call to |
528 | C<run>. The strings can be any octet string. |
660 | C<run>. The strings can be any octet string. |
529 | |
661 | |
|
|
662 | The protocol is optimised to pass a moderate number of relatively short |
|
|
663 | strings - while you can pass up to 4GB of data in one go, this is more |
|
|
664 | meant to pass some ID information or other startup info, not big chunks of |
|
|
665 | data. |
|
|
666 | |
530 | Returns the process object for easy chaining of emthod calls. |
667 | Returns the process object for easy chaining of method calls. |
531 | |
668 | |
532 | =cut |
669 | =cut |
533 | |
670 | |
534 | sub send_arg { |
671 | sub send_arg { |
535 | my ($self, @arg) = @_; |
672 | my ($self, @arg) = @_; |
536 | |
673 | |
537 | $self->_cmd (a => @arg); |
674 | $self->_cmd (a => pack "(w/a*)*", @arg); |
538 | |
675 | |
539 | $self |
676 | $self |
540 | } |
677 | } |
541 | |
678 | |
542 | =item $proc->run ($func, $cb->($fh)) |
679 | =item $proc->run ($func, $cb->($fh)) |
543 | |
680 | |
544 | Enter the function specified by the fully qualified name in C<$func> in |
681 | Enter the function specified by the function name in C<$func> in the |
545 | the process. The function is called with the communication socket as first |
682 | process. The function is called with the communication socket as first |
546 | argument, followed by all file handles and string arguments sent earlier |
683 | argument, followed by all file handles and string arguments sent earlier |
547 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
684 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
548 | |
685 | |
549 | If the called function returns, the process exits. |
686 | The function name should be fully qualified, but if it isn't, it will be |
|
|
687 | looked up in the main package. |
550 | |
688 | |
551 | Preparing the process can take time - when the process is ready, the |
689 | If the called function returns, doesn't exist, or any error occurs, the |
|
|
690 | process exits. |
|
|
691 | |
|
|
692 | Preparing the process is done in the background - when all commands have |
552 | callback is invoked with the local communications socket as argument. |
693 | been sent, the callback is invoked with the local communications socket |
|
|
694 | as argument. At this point you can start using the socket in any way you |
|
|
695 | like. |
553 | |
696 | |
554 | The process object becomes unusable on return from this function. |
697 | The process object becomes unusable on return from this function - any |
|
|
698 | further method calls result in undefined behaviour. |
555 | |
699 | |
556 | If the communication socket isn't used, it should be closed on both sides, |
700 | If the communication socket isn't used, it should be closed on both sides, |
557 | to save on kernel memory. |
701 | to save on kernel memory. |
558 | |
702 | |
559 | The socket is non-blocking in the parent, and blocking in the newly |
703 | The socket is non-blocking in the parent, and blocking in the newly |
560 | created process. The close-on-exec flag is set on both. Even if not used |
704 | created process. The close-on-exec flag is set in both. |
|
|
705 | |
561 | otherwise, the socket can be a good indicator for the existance of the |
706 | Even if not used otherwise, the socket can be a good indicator for the |
562 | process - if the other process exits, you get a readable event on it, |
707 | existence of the process - if the other process exits, you get a readable |
563 | because exiting the process closes the socket (if it didn't create any |
708 | event on it, because exiting the process closes the socket (if it didn't |
564 | children using fork). |
709 | create any children using fork). |
565 | |
710 | |
566 | Example: create a template for a process pool, pass a few strings, some |
711 | Example: create a template for a process pool, pass a few strings, some |
567 | file handles, then fork, pass one more string, and run some code. |
712 | file handles, then fork, pass one more string, and run some code. |
568 | |
713 | |
569 | my $pool = AnyEvent::Fork |
714 | my $pool = AnyEvent::Fork |
… | |
… | |
577 | ->send_arg ("str3") |
722 | ->send_arg ("str3") |
578 | ->run ("Some::function", sub { |
723 | ->run ("Some::function", sub { |
579 | my ($fh) = @_; |
724 | my ($fh) = @_; |
580 | |
725 | |
581 | # fh is nonblocking, but we trust that the OS can accept these |
726 | # fh is nonblocking, but we trust that the OS can accept these |
582 | # extra 3 octets anyway. |
727 | # few octets anyway. |
583 | syswrite $fh, "hi #$_\n"; |
728 | syswrite $fh, "hi #$_\n"; |
584 | |
729 | |
585 | # $fh is being closed here, as we don't store it anywhere |
730 | # $fh is being closed here, as we don't store it anywhere |
586 | }); |
731 | }); |
587 | } |
732 | } |
… | |
… | |
589 | # Some::function might look like this - all parameters passed before fork |
734 | # Some::function might look like this - all parameters passed before fork |
590 | # and after will be passed, in order, after the communications socket. |
735 | # and after will be passed, in order, after the communications socket. |
591 | sub Some::function { |
736 | sub Some::function { |
592 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
737 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
593 | |
738 | |
594 | print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" |
739 | print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order |
595 | } |
740 | } |
596 | |
741 | |
597 | =cut |
742 | =cut |
598 | |
743 | |
599 | sub run { |
744 | sub run { |
600 | my ($self, $func, $cb) = @_; |
745 | my ($self, $func, $cb) = @_; |
601 | |
746 | |
602 | $self->[0] = $cb; |
747 | $self->[4] = $cb; |
603 | $self->_cmd (r => $func); |
748 | $self->_cmd (r => $func); |
604 | } |
749 | } |
|
|
750 | |
|
|
751 | =back |
|
|
752 | |
|
|
753 | =head1 PERFORMANCE |
|
|
754 | |
|
|
755 | Now for some unscientific benchmark numbers (all done on an amd64 |
|
|
756 | GNU/Linux box). These are intended to give you an idea of the relative |
|
|
757 | performance you can expect, they are not meant to be absolute performance |
|
|
758 | numbers. |
|
|
759 | |
|
|
760 | OK, so, I ran a simple benchmark that creates a socket pair, forks, calls |
|
|
761 | exit in the child and waits for the socket to close in the parent. I did |
|
|
762 | load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB. |
|
|
763 | |
|
|
764 | 2079 new processes per second, using manual socketpair + fork |
|
|
765 | |
|
|
766 | Then I did the same thing, but instead of calling fork, I called |
|
|
767 | AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the |
|
|
768 | socket form the child to close on exit. This does the same thing as manual |
|
|
769 | socket pair + fork, except that what is forked is the template process |
|
|
770 | (2440kB), and the socket needs to be passed to the server at the other end |
|
|
771 | of the socket first. |
|
|
772 | |
|
|
773 | 2307 new processes per second, using AnyEvent::Fork->new |
|
|
774 | |
|
|
775 | And finally, using C<new_exec> instead C<new>, using vforks+execs to exec |
|
|
776 | a new perl interpreter and compile the small server each time, I get: |
|
|
777 | |
|
|
778 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
|
|
779 | |
|
|
780 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
|
|
781 | though it uses the same operations, but adds a lot of overhead? |
|
|
782 | |
|
|
783 | The difference is simply the process size: forking the 6MB process takes |
|
|
784 | so much longer than forking the 2.5MB template process that the overhead |
|
|
785 | introduced is canceled out. |
|
|
786 | |
|
|
787 | If the benchmark process grows, the normal fork becomes even slower: |
|
|
788 | |
|
|
789 | 1340 new processes, manual fork in a 20MB process |
|
|
790 | 731 new processes, manual fork in a 200MB process |
|
|
791 | 235 new processes, manual fork in a 2000MB process |
|
|
792 | |
|
|
793 | What that means (to me) is that I can use this module without having a |
|
|
794 | very bad conscience because of the extra overhead required to start new |
|
|
795 | processes. |
|
|
796 | |
|
|
797 | =head1 TYPICAL PROBLEMS |
|
|
798 | |
|
|
799 | This section lists typical problems that remain. I hope by recognising |
|
|
800 | them, most can be avoided. |
|
|
801 | |
|
|
802 | =over 4 |
|
|
803 | |
|
|
804 | =item "leaked" file descriptors for exec'ed processes |
|
|
805 | |
|
|
806 | POSIX systems inherit file descriptors by default when exec'ing a new |
|
|
807 | process. While perl itself laudably sets the close-on-exec flags on new |
|
|
808 | file handles, most C libraries don't care, and even if all cared, it's |
|
|
809 | often not possible to set the flag in a race-free manner. |
|
|
810 | |
|
|
811 | That means some file descriptors can leak through. And since it isn't |
|
|
812 | possible to know which file descriptors are "good" and "necessary" (or |
|
|
813 | even to know which file descriptors are open), there is no good way to |
|
|
814 | close the ones that might harm. |
|
|
815 | |
|
|
816 | As an example of what "harm" can be done consider a web server that |
|
|
817 | accepts connections and afterwards some module uses AnyEvent::Fork for the |
|
|
818 | first time, causing it to fork and exec a new process, which might inherit |
|
|
819 | the network socket. When the server closes the socket, it is still open |
|
|
820 | in the child (which doesn't even know that) and the client might conclude |
|
|
821 | that the connection is still fine. |
|
|
822 | |
|
|
823 | For the main program, there are multiple remedies available - |
|
|
824 | L<AnyEvent::Fork::Early> is one, creating a process early and not using |
|
|
825 | C<new_exec> is another, as in both cases, the first process can be exec'ed |
|
|
826 | well before many random file descriptors are open. |
|
|
827 | |
|
|
828 | In general, the solution for these kind of problems is to fix the |
|
|
829 | libraries or the code that leaks those file descriptors. |
|
|
830 | |
|
|
831 | Fortunately, most of these leaked descriptors do no harm, other than |
|
|
832 | sitting on some resources. |
|
|
833 | |
|
|
834 | =item "leaked" file descriptors for fork'ed processes |
|
|
835 | |
|
|
836 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
|
|
837 | which closes file descriptors not marked for being inherited. |
|
|
838 | |
|
|
839 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
|
|
840 | a way to create these processes by forking, and this leaks more file |
|
|
841 | descriptors than exec'ing them, as there is no way to mark descriptors as |
|
|
842 | "close on fork". |
|
|
843 | |
|
|
844 | An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create |
|
|
845 | pipes for internal uses, and L<Gtk2> might open a connection to the X |
|
|
846 | server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have |
|
|
847 | trouble with a fork. |
|
|
848 | |
|
|
849 | The solution is to either not load these modules before use'ing |
|
|
850 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
|
|
851 | initialising them, for example, by calling C<init Gtk2> manually. |
|
|
852 | |
|
|
853 | =item exit runs destructors |
|
|
854 | |
|
|
855 | This only applies to users of Lc<AnyEvent::Fork:Early> and |
|
|
856 | L<AnyEvent::Fork::Template>. |
|
|
857 | |
|
|
858 | When a process created by AnyEvent::Fork exits, it might do so by calling |
|
|
859 | exit, or simply letting perl reach the end of the program. At which point |
|
|
860 | Perl runs all destructors. |
|
|
861 | |
|
|
862 | Not all destructors are fork-safe - for example, an object that represents |
|
|
863 | the connection to an X display might tell the X server to free resources, |
|
|
864 | which is inconvenient when the "real" object in the parent still needs to |
|
|
865 | use them. |
|
|
866 | |
|
|
867 | This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used |
|
|
868 | it as the very first thing, right? |
|
|
869 | |
|
|
870 | It is a problem for L<AnyEvent::Fork::Template> though - and the solution |
|
|
871 | is to not create objects with nontrivial destructors that might have an |
|
|
872 | effect outside of Perl. |
605 | |
873 | |
606 | =back |
874 | =back |
607 | |
875 | |
608 | =head1 PORTABILITY NOTES |
876 | =head1 PORTABILITY NOTES |
609 | |
877 | |
610 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
878 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
611 | and ::Template is not going to work), and it cost a lot of blood and sweat |
879 | and ::Template is not going to work), and it cost a lot of blood and sweat |
612 | to make it so, mostly due to the bloody broken perl that nobody seems to |
880 | to make it so, mostly due to the bloody broken perl that nobody seems to |
613 | care about. The fork emulation is a bad joke - I have yet to see something |
881 | care about. The fork emulation is a bad joke - I have yet to see something |
614 | useful that you cna do with it without running into memory corruption |
882 | useful that you can do with it without running into memory corruption |
615 | issues or other braindamage. Hrrrr. |
883 | issues or other braindamage. Hrrrr. |
616 | |
884 | |
617 | Cygwin perl is not supported at the moment, as it should implement fd |
885 | Cygwin perl is not supported at the moment, as it should implement fd |
618 | passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
886 | passing, but doesn't, and rolling my own is hard, as cygwin doesn't |
619 | support enough functionality to do it. |
887 | support enough functionality to do it. |
620 | |
888 | |
|
|
889 | =head1 SEE ALSO |
|
|
890 | |
|
|
891 | L<AnyEvent::Fork::Early> (to avoid executing a perl interpreter), |
|
|
892 | L<AnyEvent::Fork::Template> (to create a process by forking the main |
|
|
893 | program at a convenient time). |
|
|
894 | |
621 | =head1 AUTHOR |
895 | =head1 AUTHOR |
622 | |
896 | |
623 | Marc Lehmann <schmorp@schmorp.de> |
897 | Marc Lehmann <schmorp@schmorp.de> |
624 | http://home.schmorp.de/ |
898 | http://home.schmorp.de/ |
625 | |
899 | |