1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | AnyEvent::ProcessPool - manage pools of perl worker processes, exec'ed or fork'ed |
3 | AnyEvent::Fork - everything you wanted to use fork() for, but couldn't |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use AnyEvent::ProcessPool; |
7 | use AnyEvent::Fork; |
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8 | |
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9 | AnyEvent::Fork |
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10 | ->new |
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11 | ->require ("MyModule") |
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12 | ->run ("MyModule::server", my $cv = AE::cv); |
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13 | |
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14 | my $fh = $cv->recv; |
8 | |
15 | |
9 | =head1 DESCRIPTION |
16 | =head1 DESCRIPTION |
10 | |
17 | |
11 | This module allows you to create single worker processes but also worker |
18 | This module allows you to create new processes, without actually forking |
12 | pool that share memory, by forking from the main program, or exec'ing new |
19 | them from your current process (avoiding the problems of forking), but |
13 | perl interpreters from a module. |
20 | preserving most of the advantages of fork. |
14 | |
21 | |
15 | You create a new processes in a pool by specifying a function to call |
22 | It can be used to create new worker processes or new independent |
16 | with any combination of string values and file handles. |
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. |
17 | |
27 | |
18 | A pool can have initialisation code which is executed before forking. The |
28 | Special care has been taken to make this module useful from other modules, |
19 | initialisation code is only executed once and the resulting process is |
29 | while still supporting specialised environments such as L<App::Staticperl> |
20 | cached, to be used as a template. |
30 | or L<PAR::Packer>. |
21 | |
31 | |
22 | Pools without such initialisation code don't cache an extra process. |
32 | =head2 WHAT THIS MODULE IS NOT |
23 | |
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 could use the L<AnyEvent::Fork::RPC> |
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40 | companion module, which adds simple RPC/job queueing to a process created |
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41 | by this module. |
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42 | |
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43 | And if you need some automatic process pool management on top of |
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44 | L<AnyEvent::Fork::RPC>, you can look at the L<AnyEvent::Fork::Pool> |
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45 | companion module. |
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46 | |
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47 | Or you can implement it yourself in whatever way you like: use some |
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48 | message-passing module such as L<AnyEvent::MP>, some pipe such as |
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49 | L<AnyEvent::ZeroMQ>, use L<AnyEvent::Handle> on both sides to send |
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50 | e.g. JSON or Storable messages, and so on. |
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51 | |
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52 | =head2 COMPARISON TO OTHER MODULES |
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53 | |
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54 | There is an abundance of modules on CPAN that do "something fork", such as |
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55 | L<Parallel::ForkManager>, L<AnyEvent::ForkManager>, L<AnyEvent::Worker> |
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56 | or L<AnyEvent::Subprocess>. There are modules that implement their own |
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57 | process management, such as L<AnyEvent::DBI>. |
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58 | |
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59 | The problems that all these modules try to solve are real, however, none |
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60 | of them (from what I have seen) tackle the very real problems of unwanted |
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61 | memory sharing, efficiency, not being able to use event processing or |
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62 | similar modules in the processes they create. |
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63 | |
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64 | This module doesn't try to replace any of them - instead it tries to solve |
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65 | the problem of creating processes with a minimum of fuss and overhead (and |
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66 | also luxury). Ideally, most of these would use AnyEvent::Fork internally, |
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67 | except they were written before AnyEvent:Fork was available, so obviously |
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68 | had to roll their own. |
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69 | |
24 | =head1 PROBLEM STATEMENT |
70 | =head2 PROBLEM STATEMENT |
25 | |
71 | |
26 | There are two ways to implement parallel processing on UNIX like operating |
72 | There are two traditional ways to implement parallel processing on UNIX |
27 | systems - fork and process, and fork+exec and process. They have different |
73 | like operating systems - fork and process, and fork+exec and process. They |
28 | advantages and disadvantages that I describe below, together with how this |
74 | have different advantages and disadvantages that I describe below, |
29 | module tries to mitigate the disadvantages. |
75 | together with how this module tries to mitigate the disadvantages. |
30 | |
76 | |
31 | =over 4 |
77 | =over 4 |
32 | |
78 | |
33 | =item Forking from a big process can be very slow (a 5GB process needs |
79 | =item Forking from a big process can be very slow. |
34 | 0.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead |
80 | |
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81 | A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This |
35 | is often shared with exec (because you have to fork first), but in some |
82 | overhead is often shared with exec (because you have to fork first), but |
36 | circumstances (e.g. when vfork is used), fork+exec can be much faster. |
83 | in some circumstances (e.g. when vfork is used), fork+exec can be much |
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84 | faster. |
37 | |
85 | |
38 | This module can help here by telling a small(er) helper process to fork, |
86 | This module can help here by telling a small(er) helper process to fork, |
39 | or fork+exec instead. |
87 | which is faster then forking the main process, and also uses vfork where |
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88 | possible. This gives the speed of vfork, with the flexibility of fork. |
40 | |
89 | |
41 | =item Forking usually creates a copy-on-write copy of the parent |
90 | =item Forking usually creates a copy-on-write copy of the parent |
42 | process. Memory (for example, modules or data files that have been |
91 | process. |
43 | will not take additional memory). When exec'ing a new process, modules |
92 | |
44 | and data files might need to be loaded again, at extra cpu and memory |
93 | For example, modules or data files that are loaded will not use additional |
45 | cost. Likewise when forking, all data structures are copied as well - if |
94 | memory after a fork. When exec'ing a new process, modules and data files |
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95 | might need to be loaded again, at extra CPU and memory cost. But when |
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96 | forking, literally all data structures are copied - if the program frees |
46 | the program frees them and replaces them by new data, the child processes |
97 | them and replaces them by new data, the child processes will retain the |
47 | will retain the memory even if it isn't used. |
98 | old version even if it isn't used, which can suddenly and unexpectedly |
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99 | increase memory usage when freeing memory. |
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100 | |
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101 | The trade-off is between more sharing with fork (which can be good or |
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102 | bad), and no sharing with exec. |
48 | |
103 | |
49 | This module allows the main program to do a controlled fork, and allows |
104 | This module allows the main program to do a controlled fork, and allows |
50 | modules to exec processes safely at any time. When creating a custom |
105 | modules to exec processes safely at any time. When creating a custom |
51 | process pool you can take advantage of data sharing via fork without |
106 | process pool you can take advantage of data sharing via fork without |
52 | risking to share large dynamic data structures that will blow up child |
107 | risking to share large dynamic data structures that will blow up child |
53 | memory usage. |
108 | memory usage. |
54 | |
109 | |
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110 | In other words, this module puts you into control over what is being |
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111 | shared and what isn't, at all times. |
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112 | |
55 | =item Exec'ing a new perl process might be difficult and slow. For |
113 | =item Exec'ing a new perl process might be difficult. |
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114 | |
56 | example, it is not easy to find the correct path to the perl interpreter, |
115 | For example, it is not easy to find the correct path to the perl |
57 | and all modules have to be loaded from disk again. Long running processes |
116 | interpreter - C<$^X> might not be a perl interpreter at all. |
58 | might run into problems when perl is upgraded for example. |
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59 | |
117 | |
60 | This module supports creating pre-initialised perl processes to be used |
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61 | as template, and also tries hard to identify the correct path to the perl |
118 | This module tries hard to identify the correct path to the perl |
62 | interpreter. With a cooperative main program, exec'ing the interpreter |
119 | interpreter. With a cooperative main program, exec'ing the interpreter |
63 | might not even be necessary. |
120 | might not even be necessary, but even without help from the main program, |
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121 | it will still work when used from a module. |
64 | |
122 | |
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123 | =item Exec'ing a new perl process might be slow, as all necessary modules |
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124 | have to be loaded from disk again, with no guarantees of success. |
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125 | |
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126 | Long running processes might run into problems when perl is upgraded |
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127 | and modules are no longer loadable because they refer to a different |
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128 | perl version, or parts of a distribution are newer than the ones already |
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129 | loaded. |
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130 | |
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131 | This module supports creating pre-initialised perl processes to be used as |
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132 | a template for new processes. |
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133 | |
65 | =item Forking might be impossible when a program is running. For example, |
134 | =item Forking might be impossible when a program is running. |
66 | POSIX makes it almost impossible to fork from a multithreaded program and |
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67 | do anything useful in the child - strictly speaking, if your perl program |
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68 | uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>), |
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69 | you cannot call fork on the perl level anymore, at all. |
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70 | |
135 | |
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136 | For example, POSIX makes it almost impossible to fork from a |
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137 | multi-threaded program while doing anything useful in the child - in |
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138 | fact, if your perl program uses POSIX threads (even indirectly via |
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139 | e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level |
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140 | anymore without risking corruption issues on a number of operating |
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141 | systems. |
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142 | |
71 | This module can safely fork helper processes at any time, by caling |
143 | This module can safely fork helper processes at any time, by calling |
72 | fork+exec in C, in a POSIX-compatible way. |
144 | fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>). |
73 | |
145 | |
74 | =item Parallel processing with fork might be inconvenient or difficult |
146 | =item Parallel processing with fork might be inconvenient or difficult |
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147 | to implement. Modules might not work in both parent and child. |
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148 | |
75 | to implement. For example, when a program uses an event loop and creates |
149 | For example, when a program uses an event loop and creates watchers it |
76 | watchers it becomes very hard to use the event loop from a child |
150 | becomes very hard to use the event loop from a child program, as the |
77 | program, as the watchers already exist but are only meaningful in the |
151 | watchers already exist but are only meaningful in the parent. Worse, a |
78 | parent. Worse, a module might want to use such a system, not knowing |
152 | module might want to use such a module, not knowing whether another module |
79 | whether another module or the main program also does, leading to problems. |
153 | or the main program also does, leading to problems. |
80 | |
154 | |
81 | This module only lets the main program create pools by forking (because |
155 | Apart from event loops, graphical toolkits also commonly fall into the |
82 | only the main program can know when it is still safe to do so) - all other |
156 | "unsafe module" category, or just about anything that communicates with |
83 | pools are created by fork+exec, after which such modules can again be |
157 | the external world, such as network libraries and file I/O modules, which |
84 | loaded. |
158 | usually don't like being copied and then allowed to continue in two |
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159 | processes. |
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160 | |
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161 | With this module only the main program is allowed to create new processes |
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162 | by forking (because only the main program can know when it is still safe |
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163 | to do so) - all other processes are created via fork+exec, which makes it |
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164 | possible to use modules such as event loops or window interfaces safely. |
85 | |
165 | |
86 | =back |
166 | =back |
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167 | |
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168 | =head1 EXAMPLES |
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169 | |
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170 | =head2 Create a single new process, tell it to run your worker function. |
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171 | |
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172 | AnyEvent::Fork |
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173 | ->new |
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174 | ->require ("MyModule") |
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175 | ->run ("MyModule::worker, sub { |
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176 | my ($master_filehandle) = @_; |
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177 | |
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178 | # now $master_filehandle is connected to the |
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179 | # $slave_filehandle in the new process. |
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180 | }); |
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181 | |
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182 | C<MyModule> might look like this: |
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183 | |
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184 | package MyModule; |
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185 | |
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186 | sub worker { |
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187 | my ($slave_filehandle) = @_; |
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188 | |
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189 | # now $slave_filehandle is connected to the $master_filehandle |
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190 | # in the original prorcess. have fun! |
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191 | } |
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192 | |
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193 | =head2 Create a pool of server processes all accepting on the same socket. |
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194 | |
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195 | # create listener socket |
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196 | my $listener = ...; |
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197 | |
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198 | # create a pool template, initialise it and give it the socket |
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199 | my $pool = AnyEvent::Fork |
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200 | ->new |
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201 | ->require ("Some::Stuff", "My::Server") |
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202 | ->send_fh ($listener); |
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203 | |
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204 | # now create 10 identical workers |
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205 | for my $id (1..10) { |
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206 | $pool |
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207 | ->fork |
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208 | ->send_arg ($id) |
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209 | ->run ("My::Server::run"); |
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210 | } |
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211 | |
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212 | # now do other things - maybe use the filehandle provided by run |
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213 | # to wait for the processes to die. or whatever. |
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214 | |
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215 | C<My::Server> might look like this: |
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216 | |
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217 | package My::Server; |
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218 | |
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219 | sub run { |
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220 | my ($slave, $listener, $id) = @_; |
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221 | |
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222 | close $slave; # we do not use the socket, so close it to save resources |
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223 | |
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224 | # we could go ballistic and use e.g. AnyEvent here, or IO::AIO, |
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225 | # or anything we usually couldn't do in a process forked normally. |
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226 | while (my $socket = $listener->accept) { |
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227 | # do sth. with new socket |
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228 | } |
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229 | } |
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230 | |
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231 | =head2 use AnyEvent::Fork as a faster fork+exec |
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232 | |
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233 | This runs C</bin/echo hi>, with standard output redirected to F</tmp/log> |
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234 | and standard error redirected to the communications socket. It is usually |
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235 | faster than fork+exec, but still lets you prepare the environment. |
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236 | |
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237 | open my $output, ">/tmp/log" or die "$!"; |
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238 | |
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239 | AnyEvent::Fork |
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240 | ->new |
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241 | ->eval (' |
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242 | # compile a helper function for later use |
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243 | sub run { |
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244 | my ($fh, $output, @cmd) = @_; |
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245 | |
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246 | # perl will clear close-on-exec on STDOUT/STDERR |
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247 | open STDOUT, ">&", $output or die; |
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248 | open STDERR, ">&", $fh or die; |
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249 | |
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250 | exec @cmd; |
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251 | } |
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252 | ') |
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253 | ->send_fh ($output) |
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254 | ->send_arg ("/bin/echo", "hi") |
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255 | ->run ("run", my $cv = AE::cv); |
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256 | |
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257 | my $stderr = $cv->recv; |
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258 | |
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259 | =head2 For stingy users: put the worker code into a C<DATA> section. |
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260 | |
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261 | When you want to be stingy with files, you cna put your code into the |
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262 | C<DATA> section of your module (or program): |
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263 | |
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264 | use AnyEvent::Fork; |
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265 | |
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266 | AnyEvent::Fork |
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267 | ->new |
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268 | ->eval (do { local $/; <DATA> }) |
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269 | ->run ("doit", sub { ... }); |
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270 | |
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271 | __DATA__ |
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272 | |
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273 | sub doit { |
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274 | ... do something! |
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275 | } |
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276 | |
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277 | =head2 For stingy standalone programs: do not rely on external files at |
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278 | all. |
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279 | |
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280 | For single-file scripts it can be inconvenient to rely on external |
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281 | files - even when using < C<DATA> section, you still need to C<exec> |
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282 | an external perl interpreter, which might not be available when using |
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283 | L<App::Staticperl>, L<Urlader> or L<PAR::Packer> for example. |
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284 | |
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285 | Two modules help here - L<AnyEvent::Fork::Early> forks a template process |
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286 | for all further calls to C<new_exec>, and L<AnyEvent::Fork::Template> |
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287 | forks the main program as a template process. |
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288 | |
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289 | Here is how your main program should look like: |
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290 | |
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291 | #! perl |
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292 | |
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293 | # optional, as the very first thing. |
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294 | # in case modules want to create their own processes. |
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295 | use AnyEvent::Fork::Early; |
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296 | |
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297 | # next, load all modules you need in your template process |
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298 | use Example::My::Module |
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299 | use Example::Whatever; |
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300 | |
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301 | # next, put your run function definition and anything else you |
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302 | # need, but do not use code outside of BEGIN blocks. |
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303 | sub worker_run { |
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304 | my ($fh, @args) = @_; |
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305 | ... |
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306 | } |
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307 | |
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308 | # now preserve everything so far as AnyEvent::Fork object |
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309 | # in §TEMPLATE. |
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310 | use AnyEvent::Fork::Template; |
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311 | |
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312 | # do not put code outside of BEGIN blocks until here |
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313 | |
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314 | # now use the $TEMPLATE process in any way you like |
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315 | |
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316 | # for example: create 10 worker processes |
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317 | my @worker; |
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318 | my $cv = AE::cv; |
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319 | for (1..10) { |
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320 | $cv->begin; |
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321 | $TEMPLATE->fork->send_arg ($_)->run ("worker_run", sub { |
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322 | push @worker, shift; |
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323 | $cv->end; |
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324 | }); |
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325 | } |
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326 | $cv->recv; |
87 | |
327 | |
88 | =head1 CONCEPTS |
328 | =head1 CONCEPTS |
89 | |
329 | |
90 | This module can create new processes either by executing a new perl |
330 | This module can create new processes either by executing a new perl |
91 | process, or by forking from an existing "template" process. |
331 | process, or by forking from an existing "template" process. |
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332 | |
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333 | All these processes are called "child processes" (whether they are direct |
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334 | children or not), while the process that manages them is called the |
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335 | "parent process". |
92 | |
336 | |
93 | Each such process comes with its own file handle that can be used to |
337 | Each such process comes with its own file handle that can be used to |
94 | communicate with it (it's actually a socket - one end in the new process, |
338 | communicate with it (it's actually a socket - one end in the new process, |
95 | one end in the main process), and among the things you can do in it are |
339 | one end in the main process), and among the things you can do in it are |
96 | load modules, fork new processes, send file handles to it, and execute |
340 | load modules, fork new processes, send file handles to it, and execute |
… | |
… | |
108 | needed the first time. Forking from this process shares the memory used |
352 | needed the first time. Forking from this process shares the memory used |
109 | for the perl interpreter with the new process, but loading modules takes |
353 | for the perl interpreter with the new process, but loading modules takes |
110 | time, and the memory is not shared with anything else. |
354 | time, and the memory is not shared with anything else. |
111 | |
355 | |
112 | This is ideal for when you only need one extra process of a kind, with the |
356 | This is ideal for when you only need one extra process of a kind, with the |
113 | option of starting and stipping it on demand. |
357 | option of starting and stopping it on demand. |
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358 | |
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359 | Example: |
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360 | |
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361 | AnyEvent::Fork |
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362 | ->new |
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363 | ->require ("Some::Module") |
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364 | ->run ("Some::Module::run", sub { |
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365 | my ($fork_fh) = @_; |
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366 | }); |
114 | |
367 | |
115 | =item fork a new template process, load code, then fork processes off of |
368 | =item fork a new template process, load code, then fork processes off of |
116 | it and run the code |
369 | it and run the code |
117 | |
370 | |
118 | When you need to have a bunch of processes that all execute the same (or |
371 | When you need to have a bunch of processes that all execute the same (or |
… | |
… | |
124 | modules you loaded) is shared between the processes, and each new process |
377 | modules you loaded) is shared between the processes, and each new process |
125 | consumes relatively little memory of its own. |
378 | consumes relatively little memory of its own. |
126 | |
379 | |
127 | The disadvantage of this approach is that you need to create a template |
380 | The disadvantage of this approach is that you need to create a template |
128 | process for the sole purpose of forking new processes from it, but if you |
381 | process for the sole purpose of forking new processes from it, but if you |
129 | only need a fixed number of proceses you can create them, and then destroy |
382 | only need a fixed number of processes you can create them, and then destroy |
130 | the template process. |
383 | the template process. |
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384 | |
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385 | Example: |
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386 | |
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387 | my $template = AnyEvent::Fork->new->require ("Some::Module"); |
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388 | |
|
|
389 | for (1..10) { |
|
|
390 | $template->fork->run ("Some::Module::run", sub { |
|
|
391 | my ($fork_fh) = @_; |
|
|
392 | }); |
|
|
393 | } |
|
|
394 | |
|
|
395 | # at this point, you can keep $template around to fork new processes |
|
|
396 | # later, or you can destroy it, which causes it to vanish. |
131 | |
397 | |
132 | =item execute a new perl interpreter, load some code, run it |
398 | =item execute a new perl interpreter, load some code, run it |
133 | |
399 | |
134 | This is relatively slow, and doesn't allow you to share memory between |
400 | This is relatively slow, and doesn't allow you to share memory between |
135 | multiple processes. |
401 | multiple processes. |
… | |
… | |
137 | The only advantage is that you don't have to have a template process |
403 | The only advantage is that you don't have to have a template process |
138 | hanging around all the time to fork off some new processes, which might be |
404 | hanging around all the time to fork off some new processes, which might be |
139 | an advantage when there are long time spans where no extra processes are |
405 | an advantage when there are long time spans where no extra processes are |
140 | needed. |
406 | needed. |
141 | |
407 | |
|
|
408 | Example: |
|
|
409 | |
|
|
410 | AnyEvent::Fork |
|
|
411 | ->new_exec |
|
|
412 | ->require ("Some::Module") |
|
|
413 | ->run ("Some::Module::run", sub { |
|
|
414 | my ($fork_fh) = @_; |
|
|
415 | }); |
|
|
416 | |
142 | =back |
417 | =back |
143 | |
418 | |
144 | =head1 FUNCTIONS |
419 | =head1 THE C<AnyEvent::Fork> CLASS |
|
|
420 | |
|
|
421 | This module exports nothing, and only implements a single class - |
|
|
422 | C<AnyEvent::Fork>. |
|
|
423 | |
|
|
424 | There are two class constructors that both create new processes - C<new> |
|
|
425 | and C<new_exec>. The C<fork> method creates a new process by forking an |
|
|
426 | existing one and could be considered a third constructor. |
|
|
427 | |
|
|
428 | Most of the remaining methods deal with preparing the new process, by |
|
|
429 | loading code, evaluating code and sending data to the new process. They |
|
|
430 | usually return the process object, so you can chain method calls. |
|
|
431 | |
|
|
432 | If a process object is destroyed before calling its C<run> method, then |
|
|
433 | the process simply exits. After C<run> is called, all responsibility is |
|
|
434 | passed to the specified function. |
|
|
435 | |
|
|
436 | As long as there is any outstanding work to be done, process objects |
|
|
437 | resist being destroyed, so there is no reason to store them unless you |
|
|
438 | need them later - configure and forget works just fine. |
145 | |
439 | |
146 | =over 4 |
440 | =over 4 |
147 | |
441 | |
148 | =cut |
442 | =cut |
149 | |
443 | |
150 | package AnyEvent::ProcessPool; |
444 | package AnyEvent::Fork; |
151 | |
445 | |
152 | use common::sense; |
446 | use common::sense; |
153 | |
447 | |
154 | use Socket (); |
448 | use Errno (); |
155 | |
449 | |
156 | use Proc::FastSpawn; |
|
|
157 | use AnyEvent; |
450 | use AnyEvent; |
158 | use AnyEvent::ProcessPool::Util; |
|
|
159 | use AnyEvent::Util (); |
451 | use AnyEvent::Util (); |
160 | |
452 | |
161 | BEGIN { |
453 | use IO::FDPass; |
162 | # require Exporter; |
|
|
163 | } |
|
|
164 | |
454 | |
165 | =item my $pool = new AnyEvent::ProcessPool key => value... |
455 | our $VERSION = 1.1; |
166 | |
456 | |
167 | Create a new process pool. The following named parameters are supported: |
457 | # the early fork template process |
|
|
458 | our $EARLY; |
168 | |
459 | |
169 | =over 4 |
|
|
170 | |
|
|
171 | =back |
|
|
172 | |
|
|
173 | =cut |
|
|
174 | |
|
|
175 | # the template process |
460 | # the empty template process |
176 | our $template; |
461 | our $TEMPLATE; |
177 | |
462 | |
178 | sub _queue { |
463 | sub QUEUE() { 0 } |
179 | my ($pid, $fh) = @_; |
464 | sub FH() { 1 } |
|
|
465 | sub WW() { 2 } |
|
|
466 | sub PID() { 3 } |
|
|
467 | sub CB() { 4 } |
180 | |
468 | |
181 | [ |
469 | sub _new { |
|
|
470 | my ($self, $fh, $pid) = @_; |
|
|
471 | |
|
|
472 | AnyEvent::Util::fh_nonblocking $fh, 1; |
|
|
473 | |
|
|
474 | $self = bless [ |
|
|
475 | [], # write queue - strings or fd's |
|
|
476 | $fh, |
|
|
477 | undef, # AE watcher |
182 | $pid, |
478 | $pid, |
183 | $fh, |
479 | ], $self; |
184 | [], |
|
|
185 | undef |
|
|
186 | ] |
|
|
187 | } |
|
|
188 | |
480 | |
|
|
481 | $self |
|
|
482 | } |
|
|
483 | |
189 | sub queue_cmd { |
484 | sub _cmd { |
190 | my $queue = shift; |
485 | my $self = shift; |
191 | |
486 | |
192 | push @{ $queue->[2] }, pack "N/a", pack "a (w/a)*", @_; |
487 | # ideally, we would want to use "a (w/a)*" as format string, but perl |
|
|
488 | # versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack |
|
|
489 | # it. |
|
|
490 | push @{ $self->[QUEUE] }, pack "a L/a*", $_[0], $_[1]; |
193 | |
491 | |
194 | $queue->[3] ||= AE::io $queue->[1], 1, sub { |
492 | $self->[WW] ||= AE::io $self->[FH], 1, sub { |
|
|
493 | do { |
|
|
494 | # send the next "thing" in the queue - either a reference to an fh, |
|
|
495 | # or a plain string. |
|
|
496 | |
195 | if (ref $queue->[2][0]) { |
497 | if (ref $self->[QUEUE][0]) { |
196 | AnyEvent::ProcessPool::Util::fd_send fileno $queue->[1], fileno ${ $queue->[2][0] } |
498 | # send fh |
|
|
499 | unless (IO::FDPass::send fileno $self->[FH], fileno ${ $self->[QUEUE][0] }) { |
|
|
500 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
|
|
501 | undef $self->[WW]; |
|
|
502 | die "AnyEvent::Fork: file descriptor send failure: $!"; |
|
|
503 | } |
|
|
504 | |
197 | and shift @{ $queue->[2] }; |
505 | shift @{ $self->[QUEUE] }; |
|
|
506 | |
198 | } else { |
507 | } else { |
|
|
508 | # send string |
199 | my $len = syswrite $queue->[1], $queue->[2][0] |
509 | my $len = syswrite $self->[FH], $self->[QUEUE][0]; |
200 | or do { undef $queue->[3]; die "AnyEvent::ProcessPool::queue write failure: $!" }; |
510 | |
|
|
511 | unless ($len) { |
|
|
512 | return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK; |
|
|
513 | undef $self->[WW]; |
|
|
514 | die "AnyEvent::Fork: command write failure: $!"; |
|
|
515 | } |
|
|
516 | |
201 | substr $queue->[2][0], 0, $len, ""; |
517 | substr $self->[QUEUE][0], 0, $len, ""; |
202 | shift @{ $queue->[2] } unless length $queue->[2][0]; |
518 | shift @{ $self->[QUEUE] } unless length $self->[QUEUE][0]; |
|
|
519 | } |
|
|
520 | } while @{ $self->[QUEUE] }; |
|
|
521 | |
|
|
522 | # everything written |
|
|
523 | undef $self->[WW]; |
|
|
524 | |
|
|
525 | # invoke run callback, if any |
|
|
526 | if ($self->[CB]) { |
|
|
527 | $self->[CB]->($self->[FH]); |
|
|
528 | @$self = (); |
203 | } |
529 | } |
204 | |
|
|
205 | undef $queue->[3] unless @{ $queue->[2] }; |
|
|
206 | }; |
530 | }; |
207 | } |
|
|
208 | |
531 | |
209 | sub run_template { |
532 | () # make sure we don't leak the watcher |
210 | return if $template; |
533 | } |
211 | |
534 | |
|
|
535 | # fork template from current process, used by AnyEvent::Fork::Early/Template |
|
|
536 | sub _new_fork { |
212 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
537 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
213 | AnyEvent::Util::fh_nonblocking $fh, 1; |
538 | my $parent = $$; |
214 | fd_inherit fileno $slave; |
|
|
215 | |
539 | |
216 | my %env = %ENV; |
540 | my $pid = fork; |
217 | $env{PERL5LIB} = join ":", grep !ref, @INC; |
|
|
218 | |
541 | |
219 | my $pid = spawn |
542 | if ($pid eq 0) { |
220 | $^X, |
543 | require AnyEvent::Fork::Serve; |
221 | ["perl", "-MAnyEvent::ProcessPool::Serve", "-e", "AnyEvent::ProcessPool::Serve::me", fileno $slave], |
544 | $AnyEvent::Fork::Serve::OWNER = $parent; |
222 | [map "$_=$env{$_}", keys %env], |
545 | close $fh; |
223 | or die "unable to spawn AnyEvent::ProcessPool server: $!"; |
546 | $0 = "$_[1] of $parent"; |
|
|
547 | AnyEvent::Fork::Serve::serve ($slave); |
|
|
548 | exit 0; |
|
|
549 | } elsif (!$pid) { |
|
|
550 | die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; |
|
|
551 | } |
224 | |
552 | |
225 | close $slave; |
553 | AnyEvent::Fork->_new ($fh, $pid) |
226 | |
|
|
227 | $template = _queue $pid, $fh; |
|
|
228 | |
|
|
229 | my ($a, $b) = AnyEvent::Util::portable_socketpair; |
|
|
230 | |
|
|
231 | queue_cmd $template, "Iabc"; |
|
|
232 | push @{ $template->[2] }, \$b; |
|
|
233 | |
|
|
234 | use Coro::AnyEvent; Coro::AnyEvent::sleep 1; |
|
|
235 | undef $b; |
|
|
236 | die "x" . <$a>; |
|
|
237 | } |
554 | } |
|
|
555 | |
|
|
556 | =item my $proc = new AnyEvent::Fork |
|
|
557 | |
|
|
558 | Create a new "empty" perl interpreter process and returns its process |
|
|
559 | object for further manipulation. |
|
|
560 | |
|
|
561 | The new process is forked from a template process that is kept around |
|
|
562 | for this purpose. When it doesn't exist yet, it is created by a call to |
|
|
563 | C<new_exec> first and then stays around for future calls. |
|
|
564 | |
|
|
565 | =cut |
238 | |
566 | |
239 | sub new { |
567 | sub new { |
240 | my $class = shift; |
568 | my $class = shift; |
241 | |
569 | |
242 | my $self = bless { |
570 | $TEMPLATE ||= $class->new_exec; |
|
|
571 | $TEMPLATE->fork |
|
|
572 | } |
|
|
573 | |
|
|
574 | =item $new_proc = $proc->fork |
|
|
575 | |
|
|
576 | Forks C<$proc>, creating a new process, and returns the process object |
|
|
577 | of the new process. |
|
|
578 | |
|
|
579 | If any of the C<send_> functions have been called before fork, then they |
|
|
580 | will be cloned in the child. For example, in a pre-forked server, you |
|
|
581 | might C<send_fh> the listening socket into the template process, and then |
|
|
582 | keep calling C<fork> and C<run>. |
|
|
583 | |
|
|
584 | =cut |
|
|
585 | |
|
|
586 | sub fork { |
|
|
587 | my ($self) = @_; |
|
|
588 | |
|
|
589 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
|
|
590 | |
|
|
591 | $self->send_fh ($slave); |
|
|
592 | $self->_cmd ("f"); |
|
|
593 | |
|
|
594 | AnyEvent::Fork->_new ($fh) |
|
|
595 | } |
|
|
596 | |
|
|
597 | =item my $proc = new_exec AnyEvent::Fork |
|
|
598 | |
|
|
599 | Create a new "empty" perl interpreter process and returns its process |
|
|
600 | object for further manipulation. |
|
|
601 | |
|
|
602 | Unlike the C<new> method, this method I<always> spawns a new perl process |
|
|
603 | (except in some cases, see L<AnyEvent::Fork::Early> for details). This |
|
|
604 | reduces the amount of memory sharing that is possible, and is also slower. |
|
|
605 | |
|
|
606 | You should use C<new> whenever possible, except when having a template |
|
|
607 | process around is unacceptable. |
|
|
608 | |
|
|
609 | The path to the perl interpreter is divined using various methods - first |
|
|
610 | C<$^X> is investigated to see if the path ends with something that sounds |
|
|
611 | as if it were the perl interpreter. Failing this, the module falls back to |
|
|
612 | using C<$Config::Config{perlpath}>. |
|
|
613 | |
|
|
614 | The path to perl can also be overriden by setting the global variable |
|
|
615 | C<$AnyEvent::Fork::PERL> - it's value will be used for all subsequent |
|
|
616 | invocations. |
|
|
617 | |
|
|
618 | =cut |
|
|
619 | |
|
|
620 | our $PERL; |
|
|
621 | |
|
|
622 | sub new_exec { |
|
|
623 | my ($self) = @_; |
|
|
624 | |
|
|
625 | return $EARLY->fork |
|
|
626 | if $EARLY; |
|
|
627 | |
|
|
628 | unless (defined $PERL) { |
|
|
629 | # first find path of perl |
|
|
630 | my $perl = $; |
|
|
631 | |
|
|
632 | # first we try $^X, but the path must be absolute (always on win32), and end in sth. |
|
|
633 | # that looks like perl. this obviously only works for posix and win32 |
|
|
634 | unless ( |
|
|
635 | ($^O eq "MSWin32" || $perl =~ m%^/%) |
|
|
636 | && $perl =~ m%[/\\]perl(?:[0-9]+(\.[0-9]+)+)?(\.exe)?$%i |
|
|
637 | ) { |
|
|
638 | # if it doesn't look perlish enough, try Config |
|
|
639 | require Config; |
|
|
640 | $perl = $Config::Config{perlpath}; |
|
|
641 | $perl =~ s/(?:\Q$Config::Config{_exe}\E)?$/$Config::Config{_exe}/; |
243 | @_ |
642 | } |
244 | }, $class; |
|
|
245 | |
643 | |
246 | run_template; |
644 | $PERL = $perl; |
|
|
645 | } |
|
|
646 | |
|
|
647 | require Proc::FastSpawn; |
|
|
648 | |
|
|
649 | my ($fh, $slave) = AnyEvent::Util::portable_socketpair; |
|
|
650 | Proc::FastSpawn::fd_inherit (fileno $slave); |
|
|
651 | |
|
|
652 | # new fh's should always be set cloexec (due to $^F), |
|
|
653 | # but hey, not on win32, so we always clear the inherit flag. |
|
|
654 | Proc::FastSpawn::fd_inherit (fileno $fh, 0); |
|
|
655 | |
|
|
656 | # quick. also doesn't work in win32. of course. what did you expect |
|
|
657 | #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; |
|
|
658 | my %env = %ENV; |
|
|
659 | $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; |
|
|
660 | |
|
|
661 | my $pid = Proc::FastSpawn::spawn ( |
|
|
662 | $PERL, |
|
|
663 | ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], |
|
|
664 | [map "$_=$env{$_}", keys %env], |
|
|
665 | ) or die "unable to spawn AnyEvent::Fork server: $!"; |
|
|
666 | |
|
|
667 | $self->_new ($fh, $pid) |
|
|
668 | } |
|
|
669 | |
|
|
670 | =item $pid = $proc->pid |
|
|
671 | |
|
|
672 | Returns the process id of the process I<iff it is a direct child of the |
|
|
673 | process running AnyEvent::Fork>, and C<undef> otherwise. |
|
|
674 | |
|
|
675 | Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and |
|
|
676 | L<AnyEvent::Fork::Template> are direct children, and you are responsible |
|
|
677 | to clean up their zombies when they die. |
|
|
678 | |
|
|
679 | All other processes are not direct children, and will be cleaned up by |
|
|
680 | AnyEvent::Fork itself. |
|
|
681 | |
|
|
682 | =cut |
|
|
683 | |
|
|
684 | sub pid { |
|
|
685 | $_[0][PID] |
|
|
686 | } |
|
|
687 | |
|
|
688 | =item $proc = $proc->eval ($perlcode, @args) |
|
|
689 | |
|
|
690 | Evaluates the given C<$perlcode> as ... Perl code, while setting C<@_> to |
|
|
691 | the strings specified by C<@args>, in the "main" package. |
|
|
692 | |
|
|
693 | This call is meant to do any custom initialisation that might be required |
|
|
694 | (for example, the C<require> method uses it). It's not supposed to be used |
|
|
695 | to completely take over the process, use C<run> for that. |
|
|
696 | |
|
|
697 | The code will usually be executed after this call returns, and there is no |
|
|
698 | way to pass anything back to the calling process. Any evaluation errors |
|
|
699 | will be reported to stderr and cause the process to exit. |
|
|
700 | |
|
|
701 | If you want to execute some code (that isn't in a module) to take over the |
|
|
702 | process, you should compile a function via C<eval> first, and then call |
|
|
703 | it via C<run>. This also gives you access to any arguments passed via the |
|
|
704 | C<send_xxx> methods, such as file handles. See the L<use AnyEvent::Fork as |
|
|
705 | a faster fork+exec> example to see it in action. |
|
|
706 | |
|
|
707 | Returns the process object for easy chaining of method calls. |
|
|
708 | |
|
|
709 | =cut |
|
|
710 | |
|
|
711 | sub eval { |
|
|
712 | my ($self, $code, @args) = @_; |
|
|
713 | |
|
|
714 | $self->_cmd (e => pack "(w/a*)*", $code, @args); |
247 | |
715 | |
248 | $self |
716 | $self |
249 | } |
717 | } |
250 | |
718 | |
|
|
719 | =item $proc = $proc->require ($module, ...) |
|
|
720 | |
|
|
721 | Tries to load the given module(s) into the process |
|
|
722 | |
|
|
723 | Returns the process object for easy chaining of method calls. |
|
|
724 | |
|
|
725 | =cut |
|
|
726 | |
|
|
727 | sub require { |
|
|
728 | my ($self, @modules) = @_; |
|
|
729 | |
|
|
730 | s%::%/%g for @modules; |
|
|
731 | $self->eval ('require "$_.pm" for @_', @modules); |
|
|
732 | |
|
|
733 | $self |
|
|
734 | } |
|
|
735 | |
|
|
736 | =item $proc = $proc->send_fh ($handle, ...) |
|
|
737 | |
|
|
738 | Send one or more file handles (I<not> file descriptors) to the process, |
|
|
739 | to prepare a call to C<run>. |
|
|
740 | |
|
|
741 | The process object keeps a reference to the handles until they have |
|
|
742 | been passed over to the process, so you must not explicitly close the |
|
|
743 | handles. This is most easily accomplished by simply not storing the file |
|
|
744 | handles anywhere after passing them to this method - when AnyEvent::Fork |
|
|
745 | is finished using them, perl will automatically close them. |
|
|
746 | |
|
|
747 | Returns the process object for easy chaining of method calls. |
|
|
748 | |
|
|
749 | Example: pass a file handle to a process, and release it without |
|
|
750 | closing. It will be closed automatically when it is no longer used. |
|
|
751 | |
|
|
752 | $proc->send_fh ($my_fh); |
|
|
753 | undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT |
|
|
754 | |
|
|
755 | =cut |
|
|
756 | |
|
|
757 | sub send_fh { |
|
|
758 | my ($self, @fh) = @_; |
|
|
759 | |
|
|
760 | for my $fh (@fh) { |
|
|
761 | $self->_cmd ("h"); |
|
|
762 | push @{ $self->[QUEUE] }, \$fh; |
|
|
763 | } |
|
|
764 | |
|
|
765 | $self |
|
|
766 | } |
|
|
767 | |
|
|
768 | =item $proc = $proc->send_arg ($string, ...) |
|
|
769 | |
|
|
770 | Send one or more argument strings to the process, to prepare a call to |
|
|
771 | C<run>. The strings can be any octet strings. |
|
|
772 | |
|
|
773 | The protocol is optimised to pass a moderate number of relatively short |
|
|
774 | strings - while you can pass up to 4GB of data in one go, this is more |
|
|
775 | meant to pass some ID information or other startup info, not big chunks of |
|
|
776 | data. |
|
|
777 | |
|
|
778 | Returns the process object for easy chaining of method calls. |
|
|
779 | |
|
|
780 | =cut |
|
|
781 | |
|
|
782 | sub send_arg { |
|
|
783 | my ($self, @arg) = @_; |
|
|
784 | |
|
|
785 | $self->_cmd (a => pack "(w/a*)*", @arg); |
|
|
786 | |
|
|
787 | $self |
|
|
788 | } |
|
|
789 | |
|
|
790 | =item $proc->run ($func, $cb->($fh)) |
|
|
791 | |
|
|
792 | Enter the function specified by the function name in C<$func> in the |
|
|
793 | process. The function is called with the communication socket as first |
|
|
794 | argument, followed by all file handles and string arguments sent earlier |
|
|
795 | via C<send_fh> and C<send_arg> methods, in the order they were called. |
|
|
796 | |
|
|
797 | The process object becomes unusable on return from this function - any |
|
|
798 | further method calls result in undefined behaviour. |
|
|
799 | |
|
|
800 | The function name should be fully qualified, but if it isn't, it will be |
|
|
801 | looked up in the C<main> package. |
|
|
802 | |
|
|
803 | If the called function returns, doesn't exist, or any error occurs, the |
|
|
804 | process exits. |
|
|
805 | |
|
|
806 | Preparing the process is done in the background - when all commands have |
|
|
807 | been sent, the callback is invoked with the local communications socket |
|
|
808 | as argument. At this point you can start using the socket in any way you |
|
|
809 | like. |
|
|
810 | |
|
|
811 | If the communication socket isn't used, it should be closed on both sides, |
|
|
812 | to save on kernel memory. |
|
|
813 | |
|
|
814 | The socket is non-blocking in the parent, and blocking in the newly |
|
|
815 | created process. The close-on-exec flag is set in both. |
|
|
816 | |
|
|
817 | Even if not used otherwise, the socket can be a good indicator for the |
|
|
818 | existence of the process - if the other process exits, you get a readable |
|
|
819 | event on it, because exiting the process closes the socket (if it didn't |
|
|
820 | create any children using fork). |
|
|
821 | |
|
|
822 | Example: create a template for a process pool, pass a few strings, some |
|
|
823 | file handles, then fork, pass one more string, and run some code. |
|
|
824 | |
|
|
825 | my $pool = AnyEvent::Fork |
|
|
826 | ->new |
|
|
827 | ->send_arg ("str1", "str2") |
|
|
828 | ->send_fh ($fh1, $fh2); |
|
|
829 | |
|
|
830 | for (1..2) { |
|
|
831 | $pool |
|
|
832 | ->fork |
|
|
833 | ->send_arg ("str3") |
|
|
834 | ->run ("Some::function", sub { |
|
|
835 | my ($fh) = @_; |
|
|
836 | |
|
|
837 | # fh is nonblocking, but we trust that the OS can accept these |
|
|
838 | # few octets anyway. |
|
|
839 | syswrite $fh, "hi #$_\n"; |
|
|
840 | |
|
|
841 | # $fh is being closed here, as we don't store it anywhere |
|
|
842 | }); |
|
|
843 | } |
|
|
844 | |
|
|
845 | # Some::function might look like this - all parameters passed before fork |
|
|
846 | # and after will be passed, in order, after the communications socket. |
|
|
847 | sub Some::function { |
|
|
848 | my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; |
|
|
849 | |
|
|
850 | print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order |
|
|
851 | } |
|
|
852 | |
|
|
853 | =cut |
|
|
854 | |
|
|
855 | sub run { |
|
|
856 | my ($self, $func, $cb) = @_; |
|
|
857 | |
|
|
858 | $self->[CB] = $cb; |
|
|
859 | $self->_cmd (r => $func); |
|
|
860 | } |
|
|
861 | |
251 | =back |
862 | =back |
252 | |
863 | |
253 | =head1 AUTHOR |
864 | =head2 EXPERIMENTAL METHODS |
|
|
865 | |
|
|
866 | These methods might go away completely or change behaviour, at any time. |
|
|
867 | |
|
|
868 | =over 4 |
|
|
869 | |
|
|
870 | =item $proc->to_fh ($cb->($fh)) # EXPERIMENTAL, MIGHT BE REMOVED |
|
|
871 | |
|
|
872 | Flushes all commands out to the process and then calls the callback with |
|
|
873 | the communications socket. |
|
|
874 | |
|
|
875 | The process object becomes unusable on return from this function - any |
|
|
876 | further method calls result in undefined behaviour. |
|
|
877 | |
|
|
878 | The point of this method is to give you a file handle thta you cna pass |
|
|
879 | to another process. In that other process, you can call C<new_from_fh |
|
|
880 | AnyEvent::Fork> to create a new C<AnyEvent::Fork> object from it, thereby |
|
|
881 | effectively passing a fork object to another process. |
|
|
882 | |
|
|
883 | =cut |
|
|
884 | |
|
|
885 | sub to_fh { |
|
|
886 | my ($self, $cb) = @_; |
|
|
887 | |
|
|
888 | $self->[CB] = $cb; |
|
|
889 | |
|
|
890 | unless ($self->[WW]) { |
|
|
891 | $self->[CB]->($self->[FH]); |
|
|
892 | @$self = (); |
|
|
893 | } |
|
|
894 | } |
|
|
895 | |
|
|
896 | =item new_from_fh AnyEvent::Fork $fh # EXPERIMENTAL, MIGHT BE REMOVED |
|
|
897 | |
|
|
898 | Takes a file handle originally rceeived by the C<to_fh> method and creates |
|
|
899 | a new C<AnyEvent:Fork> object. The child process itself will not change in |
|
|
900 | any way, i.e. it will keep all the modifications done to it before calling |
|
|
901 | C<to_fh>. |
|
|
902 | |
|
|
903 | The new object is very much like the original object, except that the |
|
|
904 | C<pid> method will return C<undef> even if the process is a direct child. |
|
|
905 | |
|
|
906 | =cut |
|
|
907 | |
|
|
908 | sub new_from_fh { |
|
|
909 | my ($class, $fh) = @_; |
|
|
910 | |
|
|
911 | $class->_new ($fh) |
|
|
912 | } |
|
|
913 | |
|
|
914 | =back |
|
|
915 | |
|
|
916 | =head1 PERFORMANCE |
|
|
917 | |
|
|
918 | Now for some unscientific benchmark numbers (all done on an amd64 |
|
|
919 | GNU/Linux box). These are intended to give you an idea of the relative |
|
|
920 | performance you can expect, they are not meant to be absolute performance |
|
|
921 | numbers. |
|
|
922 | |
|
|
923 | OK, so, I ran a simple benchmark that creates a socket pair, forks, calls |
|
|
924 | exit in the child and waits for the socket to close in the parent. I did |
|
|
925 | load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB. |
|
|
926 | |
|
|
927 | 2079 new processes per second, using manual socketpair + fork |
|
|
928 | |
|
|
929 | Then I did the same thing, but instead of calling fork, I called |
|
|
930 | AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the |
|
|
931 | socket from the child to close on exit. This does the same thing as manual |
|
|
932 | socket pair + fork, except that what is forked is the template process |
|
|
933 | (2440kB), and the socket needs to be passed to the server at the other end |
|
|
934 | of the socket first. |
|
|
935 | |
|
|
936 | 2307 new processes per second, using AnyEvent::Fork->new |
|
|
937 | |
|
|
938 | And finally, using C<new_exec> instead C<new>, using vforks+execs to exec |
|
|
939 | a new perl interpreter and compile the small server each time, I get: |
|
|
940 | |
|
|
941 | 479 vfork+execs per second, using AnyEvent::Fork->new_exec |
|
|
942 | |
|
|
943 | So how can C<< AnyEvent->new >> be faster than a standard fork, even |
|
|
944 | though it uses the same operations, but adds a lot of overhead? |
|
|
945 | |
|
|
946 | The difference is simply the process size: forking the 5MB process takes |
|
|
947 | so much longer than forking the 2.5MB template process that the extra |
|
|
948 | overhead is canceled out. |
|
|
949 | |
|
|
950 | If the benchmark process grows, the normal fork becomes even slower: |
|
|
951 | |
|
|
952 | 1340 new processes, manual fork of a 20MB process |
|
|
953 | 731 new processes, manual fork of a 200MB process |
|
|
954 | 235 new processes, manual fork of a 2000MB process |
|
|
955 | |
|
|
956 | What that means (to me) is that I can use this module without having a bad |
|
|
957 | conscience because of the extra overhead required to start new processes. |
|
|
958 | |
|
|
959 | =head1 TYPICAL PROBLEMS |
|
|
960 | |
|
|
961 | This section lists typical problems that remain. I hope by recognising |
|
|
962 | them, most can be avoided. |
|
|
963 | |
|
|
964 | =over 4 |
|
|
965 | |
|
|
966 | =item leaked file descriptors for exec'ed processes |
|
|
967 | |
|
|
968 | POSIX systems inherit file descriptors by default when exec'ing a new |
|
|
969 | process. While perl itself laudably sets the close-on-exec flags on new |
|
|
970 | file handles, most C libraries don't care, and even if all cared, it's |
|
|
971 | often not possible to set the flag in a race-free manner. |
|
|
972 | |
|
|
973 | That means some file descriptors can leak through. And since it isn't |
|
|
974 | possible to know which file descriptors are "good" and "necessary" (or |
|
|
975 | even to know which file descriptors are open), there is no good way to |
|
|
976 | close the ones that might harm. |
|
|
977 | |
|
|
978 | As an example of what "harm" can be done consider a web server that |
|
|
979 | accepts connections and afterwards some module uses AnyEvent::Fork for the |
|
|
980 | first time, causing it to fork and exec a new process, which might inherit |
|
|
981 | the network socket. When the server closes the socket, it is still open |
|
|
982 | in the child (which doesn't even know that) and the client might conclude |
|
|
983 | that the connection is still fine. |
|
|
984 | |
|
|
985 | For the main program, there are multiple remedies available - |
|
|
986 | L<AnyEvent::Fork::Early> is one, creating a process early and not using |
|
|
987 | C<new_exec> is another, as in both cases, the first process can be exec'ed |
|
|
988 | well before many random file descriptors are open. |
|
|
989 | |
|
|
990 | In general, the solution for these kind of problems is to fix the |
|
|
991 | libraries or the code that leaks those file descriptors. |
|
|
992 | |
|
|
993 | Fortunately, most of these leaked descriptors do no harm, other than |
|
|
994 | sitting on some resources. |
|
|
995 | |
|
|
996 | =item leaked file descriptors for fork'ed processes |
|
|
997 | |
|
|
998 | Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, |
|
|
999 | which closes file descriptors not marked for being inherited. |
|
|
1000 | |
|
|
1001 | However, L<AnyEvent::Fork::Early> and L<AnyEvent::Fork::Template> offer |
|
|
1002 | a way to create these processes by forking, and this leaks more file |
|
|
1003 | descriptors than exec'ing them, as there is no way to mark descriptors as |
|
|
1004 | "close on fork". |
|
|
1005 | |
|
|
1006 | An example would be modules like L<EV>, L<IO::AIO> or L<Gtk2>. Both create |
|
|
1007 | pipes for internal uses, and L<Gtk2> might open a connection to the X |
|
|
1008 | server. L<EV> and L<IO::AIO> can deal with fork, but Gtk2 might have |
|
|
1009 | trouble with a fork. |
|
|
1010 | |
|
|
1011 | The solution is to either not load these modules before use'ing |
|
|
1012 | L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay |
|
|
1013 | initialising them, for example, by calling C<init Gtk2> manually. |
|
|
1014 | |
|
|
1015 | =item exiting calls object destructors |
|
|
1016 | |
|
|
1017 | This only applies to users of L<AnyEvent::Fork:Early> and |
|
|
1018 | L<AnyEvent::Fork::Template>, or when initialising code creates objects |
|
|
1019 | that reference external resources. |
|
|
1020 | |
|
|
1021 | When a process created by AnyEvent::Fork exits, it might do so by calling |
|
|
1022 | exit, or simply letting perl reach the end of the program. At which point |
|
|
1023 | Perl runs all destructors. |
|
|
1024 | |
|
|
1025 | Not all destructors are fork-safe - for example, an object that represents |
|
|
1026 | the connection to an X display might tell the X server to free resources, |
|
|
1027 | which is inconvenient when the "real" object in the parent still needs to |
|
|
1028 | use them. |
|
|
1029 | |
|
|
1030 | This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used |
|
|
1031 | it as the very first thing, right? |
|
|
1032 | |
|
|
1033 | It is a problem for L<AnyEvent::Fork::Template> though - and the solution |
|
|
1034 | is to not create objects with nontrivial destructors that might have an |
|
|
1035 | effect outside of Perl. |
|
|
1036 | |
|
|
1037 | =back |
|
|
1038 | |
|
|
1039 | =head1 PORTABILITY NOTES |
|
|
1040 | |
|
|
1041 | Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, |
|
|
1042 | and ::Template is not going to work), and it cost a lot of blood and sweat |
|
|
1043 | to make it so, mostly due to the bloody broken perl that nobody seems to |
|
|
1044 | care about. The fork emulation is a bad joke - I have yet to see something |
|
|
1045 | useful that you can do with it without running into memory corruption |
|
|
1046 | issues or other braindamage. Hrrrr. |
|
|
1047 | |
|
|
1048 | Since fork is endlessly broken on win32 perls (it doesn't even remotely |
|
|
1049 | work within it's documented limits) and quite obviously it's not getting |
|
|
1050 | improved any time soon, the best way to proceed on windows would be to |
|
|
1051 | always use C<new_exec> and thus never rely on perl's fork "emulation". |
|
|
1052 | |
|
|
1053 | Cygwin perl is not supported at the moment due to some hilarious |
|
|
1054 | shortcomings of its API - see L<IO::FDPoll> for more details. If you never |
|
|
1055 | use C<send_fh> and always use C<new_exec> to create processes, it should |
|
|
1056 | work though. |
|
|
1057 | |
|
|
1058 | =head1 SEE ALSO |
|
|
1059 | |
|
|
1060 | L<AnyEvent::Fork::Early>, to avoid executing a perl interpreter at all |
|
|
1061 | (part of this distribution). |
|
|
1062 | |
|
|
1063 | L<AnyEvent::Fork::Template>, to create a process by forking the main |
|
|
1064 | program at a convenient time (part of this distribution). |
|
|
1065 | |
|
|
1066 | L<AnyEvent::Fork::RPC>, for simple RPC to child processes (on CPAN). |
|
|
1067 | |
|
|
1068 | L<AnyEvent::Fork::Pool>, for simple worker process pool (on CPAN). |
|
|
1069 | |
|
|
1070 | =head1 AUTHOR AND CONTACT INFORMATION |
254 | |
1071 | |
255 | Marc Lehmann <schmorp@schmorp.de> |
1072 | Marc Lehmann <schmorp@schmorp.de> |
256 | http://home.schmorp.de/ |
1073 | http://software.schmorp.de/pkg/AnyEvent-Fork |
257 | |
1074 | |
258 | =cut |
1075 | =cut |
259 | |
1076 | |
260 | 1 |
1077 | 1 |
261 | |
1078 | |