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34 | concurrently in the child, using AnyEvent. |
34 | concurrently in the child, using AnyEvent. |
35 | |
35 | |
36 | It also implements an asynchronous event mechanism from the child to the |
36 | It also implements an asynchronous event mechanism from the child to the |
37 | parent, that could be used for progress indications or other information. |
37 | parent, that could be used for progress indications or other information. |
38 | |
38 | |
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39 | =head1 EXAMPLES |
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40 | |
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41 | =head2 Synchronous Backend |
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42 | |
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43 | Here is a simple example that implements a backend that executes C<unlink> |
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44 | and C<rmdir> calls, and reports their status back. It also reports the |
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45 | number of requests it has processed every three requests, which is clearly |
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46 | silly, but illustrates the use of events. |
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47 | |
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48 | First the parent process: |
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49 | |
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50 | use AnyEvent; |
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51 | use AnyEvent::Fork; |
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52 | use AnyEvent::Fork::RPC; |
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53 | |
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54 | my $done = AE::cv; |
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55 | |
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56 | my $rpc = AnyEvent::Fork |
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57 | ->new |
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58 | ->require ("MyWorker") |
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59 | ->AnyEvent::Fork::RPC::run ("MyWorker::run", |
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60 | on_error => sub { warn "FATAL: $_[0]"; exit 1 }, |
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61 | on_event => sub { warn "$_[0] requests handled\n" }, |
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62 | on_destroy => $done, |
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63 | ); |
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64 | |
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65 | for my $id (1..6) { |
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66 | $rpc->(rmdir => "/tmp/somepath/$id", sub { |
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67 | $_[0] |
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68 | or warn "/tmp/somepath/$id: $_[1]\n"; |
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69 | }); |
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70 | } |
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71 | |
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72 | undef $rpc; |
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73 | |
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74 | $done->recv; |
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75 | |
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76 | The parent creates the process, queues a few rmdir's. It then forgets |
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77 | about the C<$rpc> object, so that the child exits after it has handled the |
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78 | requests, and then it waits till the requests have been handled. |
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79 | |
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80 | The child is implemented using a separate module, C<MyWorker>, shown here: |
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81 | |
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82 | package MyWorker; |
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83 | |
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84 | my $count; |
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85 | |
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86 | sub run { |
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87 | my ($cmd, $path) = @_; |
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88 | |
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89 | AnyEvent::Fork::RPC::event ($count) |
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90 | unless ++$count % 3; |
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91 | |
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92 | my $status = $cmd eq "rmdir" ? rmdir $path |
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93 | : $cmd eq "unlink" ? unlink $path |
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94 | : die "fatal error, illegal command '$cmd'"; |
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95 | |
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96 | $status or (0, "$!") |
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97 | } |
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98 | |
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99 | 1 |
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100 | |
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101 | The C<run> function first sends a "progress" event every three calls, and |
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102 | then executes C<rmdir> or C<unlink>, depending on the first parameter (or |
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103 | dies with a fatal error - obviously, you must never let this happen :). |
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104 | |
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105 | Eventually it returns the status value true if the command was successful, |
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106 | or the status value 0 and the stringified error message. |
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107 | |
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108 | On my system, running the first cdoe fragment with the given |
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109 | F<MyWorker.pm> in the current directory yields: |
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110 | |
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111 | /tmp/somepath/1: No such file or directory |
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112 | /tmp/somepath/2: No such file or directory |
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113 | 3 requests handled |
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114 | /tmp/somepath/3: No such file or directory |
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115 | /tmp/somepath/4: No such file or directory |
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116 | /tmp/somepath/5: No such file or directory |
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117 | 6 requests handled |
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118 | /tmp/somepath/6: No such file or directory |
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119 | |
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120 | Obviously, none of the directories I am trying to delete even exist. Also, |
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121 | the events and responses are processed in exactly the same order as |
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122 | they were created in the child, which is true for both synchronous and |
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123 | asynchronous backends. |
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124 | |
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125 | Note that the parentheses in the call to C<AnyEvent::Fork::RPC::event> are |
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126 | not optional. That is because the function isn't defined when the code is |
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127 | compiled. You can make sure it is visible by pre-loading the correct |
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128 | backend module in the call to C<require>: |
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129 | |
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130 | ->require ("AnyEvent::Fork::RPC::Sync", "MyWorker") |
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131 | |
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132 | Since the backend module declares the C<event> function, loading it first |
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133 | ensures that perl will correctly interpret calls to it. |
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134 | |
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135 | And as a final remark, there is a fine module on CPAN that can |
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136 | asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently |
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137 | than this example, namely L<IO::AIO>. |
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138 | |
39 | =head1 PARENT PROCESS USAGE |
139 | =head1 PARENT PROCESS USAGE |
40 | |
140 | |
41 | This module exports nothing, and only implements a single function: |
141 | This module exports nothing, and only implements a single function: |
42 | |
142 | |
43 | =over 4 |
143 | =over 4 |
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… | |
92 | Called for every call to the C<AnyEvent::Fork::RPC::event> function in the |
192 | Called for every call to the C<AnyEvent::Fork::RPC::event> function in the |
93 | child, with the arguments of that function passed to the callback. |
193 | child, with the arguments of that function passed to the callback. |
94 | |
194 | |
95 | Also called on errors when no C<on_error> handler is provided. |
195 | Also called on errors when no C<on_error> handler is provided. |
96 | |
196 | |
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197 | =item on_destroy => $cb->() |
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198 | |
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199 | Called when the C<$rpc> object has been destroyed and all requests have |
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200 | been successfully handled. This is useful when you queue some requests and |
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201 | want the child to go away after it has handled them. The problem is that |
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202 | the parent must not exit either until all requests have been handled, and |
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203 | this cna be accomplished by waiting for this callback. |
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204 | |
97 | =item init => $function (default none) |
205 | =item init => $function (default none) |
98 | |
206 | |
99 | When specified (by name), this function is called in the child as the very |
207 | When specified (by name), this function is called in the child as the very |
100 | first thing when taking over the process, with all the arguments normally |
208 | first thing when taking over the process, with all the arguments normally |
101 | passed to the C<AnyEvent::Fork::run> function, except the communications |
209 | passed to the C<AnyEvent::Fork::run> function, except the communications |
102 | socket. |
210 | socket. |
103 | |
211 | |
104 | It can be used to do one-time things in the child such as storing passed |
212 | It can be used to do one-time things in the child such as storing passed |
105 | parameters or opening database connections. |
213 | parameters or opening database connections. |
106 | |
214 | |
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215 | It is called very early - before the serialisers are created or the |
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216 | C<$function> name is resolved into a function reference, so it could be |
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217 | used to load any modules that provide the serialiser or function. It can |
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218 | not, however, create events. |
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219 | |
107 | =item async => $boolean (default: 0) |
220 | =item async => $boolean (default: 0) |
108 | |
221 | |
109 | The default server used in the child does all I/O blockingly, and only |
222 | The default server used in the child does all I/O blockingly, and only |
110 | allows a single RPC call to execute concurrently. |
223 | allows a single RPC call to execute concurrently. |
111 | |
224 | |
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116 | the calling semantics of the returned C<$rpc> function. |
229 | the calling semantics of the returned C<$rpc> function. |
117 | |
230 | |
118 | If you want to pre-load the actual back-end modules to enable memory |
231 | If you want to pre-load the actual back-end modules to enable memory |
119 | sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for |
232 | sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for |
120 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
233 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
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234 | |
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235 | If you use a template process and want to fork both sync and async |
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236 | children, then it is permissible to laod both modules. |
121 | |
237 | |
122 | =item serialiser => $string (default: '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })') |
238 | =item serialiser => $string (default: '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })') |
123 | |
239 | |
124 | All arguments, result data and event data have to be serialised to be |
240 | All arguments, result data and event data have to be serialised to be |
125 | transferred between the processes. For this, they have to be frozen and |
241 | transferred between the processes. For this, they have to be frozen and |
… | |
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142 | |
258 | |
143 | =cut |
259 | =cut |
144 | |
260 | |
145 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
261 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
146 | |
262 | |
147 | # ideally, we want (SvLEN - SvCUR) || 1024 or somesuch... |
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148 | sub rlen($) { ($_[0] < 384 ? 512 + 16 : 2 << int +(log $_[0] + 512) / log 2) - $_[0] - 16 } |
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149 | |
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150 | sub run { |
263 | sub run { |
151 | my ($self, $function, %arg) = @_; |
264 | my ($self, $function, %arg) = @_; |
152 | |
265 | |
153 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
266 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
154 | my $on_event = delete $arg{on_event}; |
267 | my $on_event = delete $arg{on_event}; |
155 | my $on_error = delete $arg{on_error}; |
268 | my $on_error = delete $arg{on_error}; |
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269 | my $on_destroy = delete $arg{on_destroy}; |
156 | |
270 | |
157 | # default for on_error is to on_event, if specified |
271 | # default for on_error is to on_event, if specified |
158 | $on_error ||= $on_event |
272 | $on_error ||= $on_event |
159 | ? sub { $on_event->(error => shift) } |
273 | ? sub { $on_event->(error => shift) } |
160 | : sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" }; |
274 | : sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" }; |
… | |
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162 | # default for on_event is to raise an error |
276 | # default for on_event is to raise an error |
163 | $on_event ||= sub { $on_error->("event received, but no on_event handler") }; |
277 | $on_event ||= sub { $on_error->("event received, but no on_event handler") }; |
164 | |
278 | |
165 | my ($f, $t) = eval $serialiser; die $@ if $@; |
279 | my ($f, $t) = eval $serialiser; die $@ if $@; |
166 | |
280 | |
167 | my (@rcb, $fh, $shutdown, $wbuf, $ww, $rbuf, $rw); |
281 | my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw); |
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282 | my ($rlen, $rbuf) = 512 - 16; |
168 | |
283 | |
169 | my $wcb = sub { |
284 | my $wcb = sub { |
170 | my $len = syswrite $fh, $wbuf; |
285 | my $len = syswrite $fh, $wbuf; |
171 | |
286 | |
172 | if (!defined $len) { |
287 | if (!defined $len) { |
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189 | $self->require ($module) |
304 | $self->require ($module) |
190 | ->send_arg ($function, $arg{init}, $serialiser) |
305 | ->send_arg ($function, $arg{init}, $serialiser) |
191 | ->run ("$module\::run", sub { |
306 | ->run ("$module\::run", sub { |
192 | $fh = shift; |
307 | $fh = shift; |
193 | $rw = AE::io $fh, 0, sub { |
308 | $rw = AE::io $fh, 0, sub { |
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309 | $rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf; |
194 | my $len = sysread $fh, $rbuf, rlen length $rbuf, length $rbuf; |
310 | my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf; |
195 | |
311 | |
196 | if ($len) { |
312 | if ($len) { |
197 | while (5 <= length $rbuf) { |
313 | while (5 <= length $rbuf) { |
198 | $len = unpack "L", $rbuf; |
314 | $len = unpack "L", $rbuf; |
199 | 4 + $len <= length $rbuf |
315 | 4 + $len <= length $rbuf |
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211 | $on_error->("unexpected data from child"); |
327 | $on_error->("unexpected data from child"); |
212 | } |
328 | } |
213 | } |
329 | } |
214 | } elsif (defined $len) { |
330 | } elsif (defined $len) { |
215 | undef $rw; undef $ww; # it ends here |
331 | undef $rw; undef $ww; # it ends here |
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332 | |
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333 | if (@rcb) { |
216 | $on_error->("unexpected eof") |
334 | $on_error->("unexpected eof"); |
217 | if @rcb; |
335 | } else { |
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336 | $on_destroy->(); |
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337 | } |
218 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
338 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
219 | undef $rw; undef $ww; # it ends here |
339 | undef $rw; undef $ww; # it ends here |
220 | $on_error->("read: $!"); |
340 | $on_error->("read: $!"); |
221 | } |
341 | } |
222 | }; |
342 | }; |
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237 | $wbuf .= pack "L/a*", &$f; |
357 | $wbuf .= pack "L/a*", &$f; |
238 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
358 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
239 | } |
359 | } |
240 | } |
360 | } |
241 | |
361 | |
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362 | =item $rpc->(..., $cb->(...)) |
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363 | |
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364 | The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code |
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365 | reference. There are two things you can do with it: call it, and let it go |
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366 | out of scope (let it get destroyed). |
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367 | |
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368 | If C<async> was false when C<$rpc> was created (the default), then, if you |
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369 | call C<$rpc>, the C<$function> is invoked with all arguments passed to |
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370 | C<$rpc> except the last one (the callback). When the function returns, the |
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371 | callback will be invoked with all the return values. |
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372 | |
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373 | If C<async> was true, then the C<$function> receives an additional |
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374 | initial argument, the result callback. In this case, returning from |
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375 | C<$function> does nothing - the function only counts as "done" when the |
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376 | result callback is called, and any arguments passed to it are considered |
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377 | the return values. This makes it possible to "return" from event handlers |
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378 | or e.g. Coro threads. |
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379 | |
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380 | The other thing that can be done with the RPC object is to destroy it. In |
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381 | this case, the child process will execute all remaining RPC calls, report |
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382 | their results, and then exit. |
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383 | |
242 | =back |
384 | =back |
243 | |
385 | |
244 | =head1 CHILD PROCESS USAGE |
386 | =head1 CHILD PROCESS USAGE |
245 | |
387 | |
246 | These functions are not available in this module. They are only available |
388 | The following function is not available in this module. They are only |
247 | in the namespace of this module when the child is running, without |
389 | available in the namespace of this module when the child is running, |
248 | having to load any extra module. They are part of the child-side API of |
390 | without having to load any extra modules. They are part of the child-side |
249 | L<AnyEvent::Fork::RPC>. |
391 | API of L<AnyEvent::Fork::RPC>. |
250 | |
392 | |
251 | =over 4 |
393 | =over 4 |
252 | |
394 | |
253 | =item AnyEvent::Fork::RPC::event ... |
395 | =item AnyEvent::Fork::RPC::event ... |
254 | |
396 | |