1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork |
3 | AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork |
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4 | |
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5 | THE API IS NOT FINISHED, CONSIDER THIS A TECHNOLOGY DEMO |
4 | |
6 | |
5 | =head1 SYNOPSIS |
7 | =head1 SYNOPSIS |
6 | |
8 | |
7 | use AnyEvent::Fork::RPC; |
9 | use AnyEvent::Fork::RPC; |
8 | # use AnyEvent::Fork is not needed |
10 | # use AnyEvent::Fork is not needed |
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12 | ->require ("MyModule") |
14 | ->require ("MyModule") |
13 | ->AnyEvent::Fork::RPC::run ( |
15 | ->AnyEvent::Fork::RPC::run ( |
14 | "MyModule::server", |
16 | "MyModule::server", |
15 | ); |
17 | ); |
16 | |
18 | |
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19 | use AnyEvent; |
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20 | |
17 | my $cv = AE::cv; |
21 | my $cv = AE::cv; |
18 | |
22 | |
19 | $rpc->(1, 2, 3, sub { |
23 | $rpc->(1, 2, 3, sub { |
20 | print "MyModule::server returned @_\n"; |
24 | print "MyModule::server returned @_\n"; |
21 | $cv->send; |
25 | $cv->send; |
… | |
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39 | Loading this module also always loads L<AnyEvent::Fork>, so you can make a |
43 | Loading this module also always loads L<AnyEvent::Fork>, so you can make a |
40 | separate C<use AnyEvent::Fork> if you wish, but you don't have to. |
44 | separate C<use AnyEvent::Fork> if you wish, but you don't have to. |
41 | |
45 | |
42 | =head1 EXAMPLES |
46 | =head1 EXAMPLES |
43 | |
47 | |
44 | =head2 Synchronous Backend |
48 | =head2 Example 1: Synchronous Backend |
45 | |
49 | |
46 | Here is a simple example that implements a backend that executes C<unlink> |
50 | Here is a simple example that implements a backend that executes C<unlink> |
47 | and C<rmdir> calls, and reports their status back. It also reports the |
51 | and C<rmdir> calls, and reports their status back. It also reports the |
48 | number of requests it has processed every three requests, which is clearly |
52 | number of requests it has processed every three requests, which is clearly |
49 | silly, but illustrates the use of events. |
53 | silly, but illustrates the use of events. |
50 | |
54 | |
51 | First the parent process: |
55 | First the parent process: |
52 | |
56 | |
53 | use AnyEvent; |
57 | use AnyEvent; |
54 | use AnyEvent::Fork; |
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55 | use AnyEvent::Fork::RPC; |
58 | use AnyEvent::Fork::RPC; |
56 | |
59 | |
57 | my $done = AE::cv; |
60 | my $done = AE::cv; |
58 | |
61 | |
59 | my $rpc = AnyEvent::Fork |
62 | my $rpc = AnyEvent::Fork |
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137 | |
140 | |
138 | And as a final remark, there is a fine module on CPAN that can |
141 | And as a final remark, there is a fine module on CPAN that can |
139 | asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently |
142 | asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently |
140 | than this example, namely L<IO::AIO>. |
143 | than this example, namely L<IO::AIO>. |
141 | |
144 | |
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145 | =head3 Example 1a: the same with the asynchronous backend |
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146 | |
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147 | This example only shows what needs to be changed to use the async backend |
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148 | instead. Doing this is not very useful, the purpose of this example is |
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149 | to show the minimum amount of change that is required to go from the |
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150 | synchronous to the asynchronous backend. |
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151 | |
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152 | To use the async backend in the previous example, you need to add the |
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153 | C<async> parameter to the C<AnyEvent::Fork::RPC::run> call: |
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154 | |
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155 | ->AnyEvent::Fork::RPC::run ("MyWorker::run", |
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156 | async => 1, |
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157 | ... |
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158 | |
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159 | And since the function call protocol is now changed, you need to adopt |
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160 | C<MyWorker::run> to the async API. |
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161 | |
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162 | First, you need to accept the extra initial C<$done> callback: |
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163 | |
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164 | sub run { |
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165 | my ($done, $cmd, $path) = @_; |
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166 | |
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167 | And since a response is now generated when C<$done> is called, as opposed |
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168 | to when the function returns, we need to call the C<$done> function with |
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169 | the status: |
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170 | |
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171 | $done->($status or (0, "$!")); |
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172 | |
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173 | A few remarks are in order. First, it's quite pointless to use the async |
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174 | backend for this example - but it I<is> possible. Second, you can call |
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175 | C<$done> before or after returning from the function. Third, having both |
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176 | returned from the function and having called the C<$done> callback, the |
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177 | child process may exit at any time, so you should call C<$done> only when |
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178 | you really I<are> done. |
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179 | |
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180 | =head2 Example 2: Asynchronous Backend |
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181 | |
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182 | This example implements multiple count-downs in the child, using |
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183 | L<AnyEvent> timers. While this is a bit silly (one could use timers in te |
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184 | parent just as well), it illustrates the ability to use AnyEvent in the |
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185 | child and the fact that responses can arrive in a different order then the |
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186 | requests. |
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187 | |
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188 | It also shows how to embed the actual child code into a C<__DATA__> |
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189 | section, so it doesn't need any external files at all. |
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190 | |
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191 | And when your parent process is often busy, and you have stricter timing |
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192 | requirements, then running timers in a child process suddenly doesn't look |
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193 | so silly anymore. |
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194 | |
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195 | Without further ado, here is the code: |
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196 | |
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197 | use AnyEvent; |
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198 | use AnyEvent::Fork::RPC; |
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199 | |
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200 | my $done = AE::cv; |
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201 | |
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202 | my $rpc = AnyEvent::Fork |
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203 | ->new |
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204 | ->require ("AnyEvent::Fork::RPC::Async") |
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205 | ->eval (do { local $/; <DATA> }) |
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206 | ->AnyEvent::Fork::RPC::run ("run", |
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207 | async => 1, |
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208 | on_error => sub { warn "FATAL: $_[0]"; exit 1 }, |
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209 | on_event => sub { print $_[0] }, |
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210 | on_destroy => $done, |
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211 | ); |
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212 | |
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213 | for my $count (3, 2, 1) { |
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214 | $rpc->($count, sub { |
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215 | warn "job $count finished\n"; |
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216 | }); |
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217 | } |
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218 | |
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219 | undef $rpc; |
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220 | |
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221 | $done->recv; |
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222 | |
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223 | __DATA__ |
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224 | |
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225 | # this ends up in main, as we don't use a package declaration |
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226 | |
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227 | use AnyEvent; |
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228 | |
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229 | sub run { |
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230 | my ($done, $count) = @_; |
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231 | |
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232 | my $n; |
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233 | |
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234 | AnyEvent::Fork::RPC::event "starting to count up to $count\n"; |
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235 | |
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236 | my $w; $w = AE::timer 1, 1, sub { |
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237 | ++$n; |
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238 | |
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239 | AnyEvent::Fork::RPC::event "count $n of $count\n"; |
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240 | |
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241 | if ($n == $count) { |
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242 | undef $w; |
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243 | $done->(); |
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244 | } |
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245 | }; |
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246 | } |
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247 | |
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248 | The parent part (the one before the C<__DATA__> section) isn't very |
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249 | different from the earlier examples. It sets async mode, preloads |
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250 | the backend module (so the C<AnyEvent::Fork::RPC::event> function is |
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251 | declared), uses a slightly different C<on_event> handler (which we use |
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252 | simply for logging purposes) and then, instead of loading a module with |
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253 | the actual worker code, it C<eval>'s the code from the data section in the |
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254 | child process. |
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255 | |
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256 | It then starts three countdowns, from 3 to 1 seconds downwards, destroys |
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257 | the rpc object so the example finishes eventually, and then just waits for |
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258 | the stuff to trickle in. |
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259 | |
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260 | The worker code uses the event function to log some progress messages, but |
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261 | mostly just creates a recurring one-second timer. |
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262 | |
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263 | The timer callback increments a counter, logs a message, and eventually, |
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264 | when the count has been reached, calls the finish callback. |
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265 | |
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266 | On my system, this results in the following output. Since all timers fire |
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267 | at roughly the same time, the actual order isn't guaranteed, but the order |
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268 | shown is very likely what you would get, too. |
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269 | |
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270 | starting to count up to 3 |
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271 | starting to count up to 2 |
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272 | starting to count up to 1 |
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273 | count 1 of 3 |
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274 | count 1 of 2 |
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275 | count 1 of 1 |
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276 | job 1 finished |
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277 | count 2 of 2 |
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278 | job 2 finished |
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279 | count 2 of 3 |
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280 | count 3 of 3 |
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281 | job 3 finished |
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282 | |
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283 | While the overall ordering isn't guaranteed, the async backend still |
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284 | guarantees that events and responses are delivered to the parent process |
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285 | in the exact same ordering as they were generated in the child process. |
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286 | |
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287 | And unless your system is I<very> busy, it should clearly show that the |
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288 | job started last will finish first, as it has the lowest count. |
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289 | |
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290 | This concludes the async example. Since L<AnyEvent::Fork> does not |
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291 | actually fork, you are free to use about any module in the child, not just |
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292 | L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example. |
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293 | |
142 | =head1 PARENT PROCESS USAGE |
294 | =head1 PARENT PROCESS USAGE |
143 | |
295 | |
144 | This module exports nothing, and only implements a single function: |
296 | This module exports nothing, and only implements a single function: |
145 | |
297 | |
146 | =over 4 |
298 | =over 4 |
… | |
… | |
224 | |
376 | |
225 | The default server used in the child does all I/O blockingly, and only |
377 | The default server used in the child does all I/O blockingly, and only |
226 | allows a single RPC call to execute concurrently. |
378 | allows a single RPC call to execute concurrently. |
227 | |
379 | |
228 | Setting C<async> to a true value switches to another implementation that |
380 | Setting C<async> to a true value switches to another implementation that |
229 | uses L<AnyEvent> in the child and allows multiple concurrent RPC calls. |
381 | uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it |
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382 | does not support recursion in the event loop however, blocking condvar |
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383 | calls will fail). |
230 | |
384 | |
231 | The actual API in the child is documented in the section that describes |
385 | The actual API in the child is documented in the section that describes |
232 | the calling semantics of the returned C<$rpc> function. |
386 | the calling semantics of the returned C<$rpc> function. |
233 | |
387 | |
234 | If you want to pre-load the actual back-end modules to enable memory |
388 | If you want to pre-load the actual back-end modules to enable memory |
… | |
… | |
236 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
390 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
237 | |
391 | |
238 | If you use a template process and want to fork both sync and async |
392 | If you use a template process and want to fork both sync and async |
239 | children, then it is permissible to load both modules. |
393 | children, then it is permissible to load both modules. |
240 | |
394 | |
241 | =item serialiser => $string (default: '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })') |
395 | =item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER) |
242 | |
396 | |
243 | All arguments, result data and event data have to be serialised to be |
397 | All arguments, result data and event data have to be serialised to be |
244 | transferred between the processes. For this, they have to be frozen and |
398 | transferred between the processes. For this, they have to be frozen and |
245 | thawed in both parent and child processes. |
399 | thawed in both parent and child processes. |
246 | |
400 | |
247 | By default, only octet strings can be passed between the processes, which |
401 | By default, only octet strings can be passed between the processes, which |
248 | is reasonably fast and efficient. |
402 | is reasonably fast and efficient and requires no extra modules. |
249 | |
403 | |
250 | For more complicated use cases, you can provide your own freeze and thaw |
404 | For more complicated use cases, you can provide your own freeze and thaw |
251 | functions, by specifying a string with perl source code. It's supposed to |
405 | functions, by specifying a string with perl source code. It's supposed to |
252 | return two code references when evaluated: the first receives a list of |
406 | return two code references when evaluated: the first receives a list of |
253 | perl values and must return an octet string. The second receives the octet |
407 | perl values and must return an octet string. The second receives the octet |
… | |
… | |
255 | |
409 | |
256 | If you need an external module for serialisation, then you can either |
410 | If you need an external module for serialisation, then you can either |
257 | pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use> |
411 | pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use> |
258 | or C<require> statement into the serialiser string. Or both. |
412 | or C<require> statement into the serialiser string. Or both. |
259 | |
413 | |
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414 | Here are some examples - some of them are also available as global |
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415 | variables that make them easier to use. |
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416 | |
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417 | =over 4 |
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418 | |
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419 | =item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER> |
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420 | |
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421 | This serialiser concatenates length-prefixes octet strings, and is the |
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422 | default. |
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423 | |
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424 | Implementation: |
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425 | |
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426 | ( |
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427 | sub { pack "(w/a*)*", @_ }, |
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428 | sub { unpack "(w/a*)*", shift } |
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429 | ) |
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430 | |
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431 | =item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER> |
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432 | |
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433 | This serialiser creates JSON arrays - you have to make sure the L<JSON> |
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434 | module is installed for this serialiser to work. It can be beneficial for |
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435 | sharing when you preload the L<JSON> module in a template process. |
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436 | |
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437 | L<JSON> (with L<JSON::XS> installed) is slower than the octet string |
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438 | serialiser, but usually much faster than L<Storable>, unless big chunks of |
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439 | binary data need to be transferred. |
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440 | |
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441 | Implementation: |
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442 | |
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443 | use JSON (); |
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444 | ( |
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445 | sub { JSON::encode_json \@_ }, |
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446 | sub { @{ JSON::decode_json shift } } |
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447 | ) |
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448 | |
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449 | =item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER> |
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450 | |
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451 | This serialiser uses L<Storable>, which means it has high chance of |
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452 | serialising just about anything you throw at it, at the cost of having |
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453 | very high overhead per operation. It also comes with perl. |
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454 | |
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455 | Implementation: |
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456 | |
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457 | use Storable (); |
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458 | ( |
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459 | sub { Storable::freeze \@_ }, |
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460 | sub { @{ Storable::thaw shift } } |
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461 | ) |
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462 | |
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463 | =back |
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464 | |
260 | =back |
465 | =back |
261 | |
466 | |
262 | See the examples section earlier in this document for some actual |
467 | See the examples section earlier in this document for some actual |
263 | examples. |
468 | examples. |
264 | |
469 | |
265 | =cut |
470 | =cut |
266 | |
471 | |
267 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
472 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
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473 | our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })'; |
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474 | our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })'; |
268 | |
475 | |
269 | sub run { |
476 | sub run { |
270 | my ($self, $function, %arg) = @_; |
477 | my ($self, $function, %arg) = @_; |
271 | |
478 | |
272 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
479 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
… | |
… | |
341 | } |
548 | } |
342 | } elsif (defined $len) { |
549 | } elsif (defined $len) { |
343 | undef $rw; undef $ww; # it ends here |
550 | undef $rw; undef $ww; # it ends here |
344 | |
551 | |
345 | if (@rcb || %rcb) { |
552 | if (@rcb || %rcb) { |
346 | use Data::Dump;ddx[\@rcb,\%rcb];#d# |
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347 | $on_error->("unexpected eof"); |
553 | $on_error->("unexpected eof"); |
348 | } else { |
554 | } else { |
349 | $on_destroy->(); |
555 | $on_destroy->(); |
350 | } |
556 | } |
351 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
557 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
… | |
… | |
431 | See the examples section earlier in this document for some actual |
637 | See the examples section earlier in this document for some actual |
432 | examples. |
638 | examples. |
433 | |
639 | |
434 | =back |
640 | =back |
435 | |
641 | |
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642 | =head1 ADVANCED TOPICS |
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643 | |
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644 | =head2 Choosing a backend |
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645 | |
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646 | So how do you decide which backend to use? Well, that's your problem to |
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647 | solve, but here are some thoughts on the matter: |
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648 | |
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649 | =over 4 |
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650 | |
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651 | =item Synchronous |
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652 | |
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653 | The synchronous backend does not rely on any external modules (well, |
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654 | except L<common::sense>, which works around a bug in how perl's warning |
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655 | system works). This keeps the process very small, for example, on my |
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656 | system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB |
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657 | after C<use warnings; use strict> (for people who grew up with C64s around |
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658 | them this is probably shocking every single time they see it). The worker |
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659 | process in the first example in this document uses 1792kB. |
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660 | |
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661 | Since the calls are done synchronously, slow jobs will keep newer jobs |
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662 | from executing. |
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663 | |
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664 | The synchronous backend also has no overhead due to running an event loop |
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665 | - reading requests is therefore very efficient, while writing responses is |
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666 | less so, as every response results in a write syscall. |
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667 | |
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668 | If the parent process is busy and a bit slow reading responses, the child |
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669 | waits instead of processing further requests. This also limits the amount |
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670 | of memory needed for buffering, as never more than one response has to be |
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671 | buffered. |
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672 | |
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673 | The API in the child is simple - you just have to define a function that |
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674 | does something and returns something. |
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675 | |
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676 | It's hard to use modules or code that relies on an event loop, as the |
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677 | child cannot execute anything while it waits for more input. |
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678 | |
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679 | =item Asynchronous |
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680 | |
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681 | The asynchronous backend relies on L<AnyEvent>, which tries to be small, |
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682 | but still comes at a price: On my system, the worker from example 1a uses |
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683 | 3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader> |
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684 | which in turn loads a lot of other modules such as L<warnings>, L<strict>, |
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685 | L<vars>, L<Exporter>...). |
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686 | |
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687 | It batches requests and responses reasonably efficiently, doing only as |
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688 | few reads and writes as needed, but needs to poll for events via the event |
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689 | loop. |
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690 | |
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691 | Responses are queued when the parent process is busy. This means the child |
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692 | can continue to execute any queued requests. It also means that a child |
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693 | might queue a lot of responses in memory when it generates them and the |
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694 | parent process is slow accepting them. |
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695 | |
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696 | The API is not a straightforward RPC pattern - you have to call a |
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697 | "done" callback to pass return values and signal completion. Also, more |
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698 | importantly, the API starts jobs as fast as possible - when 1000 jobs |
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699 | are queued and the jobs are slow, they will all run concurrently. The |
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700 | child must implement some queueing/limiting mechanism if this causes |
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701 | problems. Alternatively, the parent could limit the amount of rpc calls |
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702 | that are outstanding. |
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703 | |
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704 | Blocking use of condvars is not supported. |
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705 | |
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706 | Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is |
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707 | easy. |
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708 | |
|
|
709 | =back |
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710 | |
|
|
711 | =head2 Passing file descriptors |
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|
712 | |
|
|
713 | Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file |
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714 | descriptor passing abilities. |
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715 | |
|
|
716 | The reason is that passing file descriptors is extraordinary tricky |
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|
717 | business, and conflicts with efficient batching of messages. |
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|
718 | |
|
|
719 | There still is a method you can use: Create a |
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|
720 | C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to |
|
|
721 | the process before you pass control to C<AnyEvent::Fork::RPC::run>. |
|
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722 | |
|
|
723 | Whenever you want to pass a file descriptor, send an rpc request to the |
|
|
724 | child process (so it expects the descriptor), then send it over the other |
|
|
725 | half of the socketpair. The child should fetch the descriptor from the |
|
|
726 | half it has passed earlier. |
|
|
727 | |
|
|
728 | Here is some (untested) pseudocode to that effect: |
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|
729 | |
|
|
730 | use AnyEvent::Util; |
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|
731 | use AnyEvent::Fork::RPC; |
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|
732 | use IO::FDPass; |
|
|
733 | |
|
|
734 | my ($s1, $s2) = AnyEvent::Util::portable_socketpair; |
|
|
735 | |
|
|
736 | my $rpc = AnyEvent::Fork |
|
|
737 | ->new |
|
|
738 | ->send_fh ($s2) |
|
|
739 | ->require ("MyWorker") |
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|
740 | ->AnyEvent::Fork::RPC::run ("MyWorker::run" |
|
|
741 | init => "MyWorker::init", |
|
|
742 | ); |
|
|
743 | |
|
|
744 | undef $s2; # no need to keep it around |
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|
745 | |
|
|
746 | # pass an fd |
|
|
747 | $rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv); |
|
|
748 | |
|
|
749 | IO::FDPass fileno $s1, fileno $handle_to_pass; |
|
|
750 | |
|
|
751 | $cv->recv; |
|
|
752 | |
|
|
753 | The MyWorker module could look like this: |
|
|
754 | |
|
|
755 | package MyWorker; |
|
|
756 | |
|
|
757 | use IO::FDPass; |
|
|
758 | |
|
|
759 | my $s2; |
|
|
760 | |
|
|
761 | sub init { |
|
|
762 | $s2 = $_[0]; |
|
|
763 | } |
|
|
764 | |
|
|
765 | sub run { |
|
|
766 | if ($_[0] eq "i'll send some fd now, please expect it!") { |
|
|
767 | my $fd = IO::FDPass::recv fileno $s2; |
|
|
768 | ... |
|
|
769 | } |
|
|
770 | } |
|
|
771 | |
|
|
772 | Of course, this might be blocking if you pass a lot of file descriptors, |
|
|
773 | so you might want to look into L<AnyEvent::FDpasser> which can handle the |
|
|
774 | gory details. |
|
|
775 | |
436 | =head1 SEE ALSO |
776 | =head1 SEE ALSO |
437 | |
777 | |
438 | L<AnyEvent::Fork> (to create the processes in the first place), |
778 | L<AnyEvent::Fork>, to create the processes in the first place. |
|
|
779 | |
439 | L<AnyEvent::Fork::Pool> (to manage whole pools of processes). |
780 | L<AnyEvent::Fork::Pool>, to manage whole pools of processes. |
440 | |
781 | |
441 | =head1 AUTHOR AND CONTACT INFORMATION |
782 | =head1 AUTHOR AND CONTACT INFORMATION |
442 | |
783 | |
443 | Marc Lehmann <schmorp@schmorp.de> |
784 | Marc Lehmann <schmorp@schmorp.de> |
444 | http://software.schmorp.de/pkg/AnyEvent-Fork-RPC |
785 | http://software.schmorp.de/pkg/AnyEvent-Fork-RPC |