… | |
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2 | |
2 | |
3 | AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork |
3 | AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
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7 | use AnyEvent::Fork; |
7 | use AnyEvent::Fork::RPC; |
8 | use AnyEvent::Fork::RPC; |
8 | # use AnyEvent::Fork is not needed |
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9 | |
9 | |
10 | my $rpc = AnyEvent::Fork |
10 | my $rpc = AnyEvent::Fork |
11 | ->new |
11 | ->new |
12 | ->require ("MyModule") |
12 | ->require ("MyModule") |
13 | ->AnyEvent::Fork::RPC::run ( |
13 | ->AnyEvent::Fork::RPC::run ( |
14 | "MyModule::server", |
14 | "MyModule::server", |
15 | ); |
15 | ); |
16 | |
16 | |
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17 | use AnyEvent; |
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18 | |
17 | my $cv = AE::cv; |
19 | my $cv = AE::cv; |
18 | |
20 | |
19 | $rpc->(1, 2, 3, sub { |
21 | $rpc->(1, 2, 3, sub { |
20 | print "MyModule::server returned @_\n"; |
22 | print "MyModule::server returned @_\n"; |
21 | $cv->send; |
23 | $cv->send; |
… | |
… | |
24 | $cv->recv; |
26 | $cv->recv; |
25 | |
27 | |
26 | =head1 DESCRIPTION |
28 | =head1 DESCRIPTION |
27 | |
29 | |
28 | This module implements a simple RPC protocol and backend for processes |
30 | This module implements a simple RPC protocol and backend for processes |
29 | created via L<AnyEvent::Fork>, allowing you to call a function in the |
31 | created via L<AnyEvent::Fork> or L<AnyEvent::Fork::Remote>, allowing you |
30 | child process and receive its return values (up to 4GB serialised). |
32 | to call a function in the child process and receive its return values (up |
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33 | to 4GB serialised). |
31 | |
34 | |
32 | It implements two different backends: a synchronous one that works like a |
35 | It implements two different backends: a synchronous one that works like a |
33 | normal function call, and an asynchronous one that can run multiple jobs |
36 | normal function call, and an asynchronous one that can run multiple jobs |
34 | concurrently in the child, using AnyEvent. |
37 | concurrently in the child, using AnyEvent. |
35 | |
38 | |
36 | It also implements an asynchronous event mechanism from the child to the |
39 | It also implements an asynchronous event mechanism from the child to the |
37 | parent, that could be used for progress indications or other information. |
40 | parent, that could be used for progress indications or other information. |
38 | |
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39 | Loading this module also always loads L<AnyEvent::Fork>, so you can make a |
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40 | separate C<use AnyEvent::Fork> if you wish, but you don't have to. |
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41 | |
41 | |
42 | =head1 EXAMPLES |
42 | =head1 EXAMPLES |
43 | |
43 | |
44 | =head2 Example 1: Synchronous Backend |
44 | =head2 Example 1: Synchronous Backend |
45 | |
45 | |
… | |
… | |
49 | silly, but illustrates the use of events. |
49 | silly, but illustrates the use of events. |
50 | |
50 | |
51 | First the parent process: |
51 | First the parent process: |
52 | |
52 | |
53 | use AnyEvent; |
53 | use AnyEvent; |
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54 | use AnyEvent::Fork; |
54 | use AnyEvent::Fork::RPC; |
55 | use AnyEvent::Fork::RPC; |
55 | |
56 | |
56 | my $done = AE::cv; |
57 | my $done = AE::cv; |
57 | |
58 | |
58 | my $rpc = AnyEvent::Fork |
59 | my $rpc = AnyEvent::Fork |
59 | ->new |
60 | ->new |
60 | ->require ("MyWorker") |
61 | ->require ("MyWorker") |
61 | ->AnyEvent::Fork::RPC::run ("MyWorker::run", |
62 | ->AnyEvent::Fork::RPC::run ("MyWorker::run", |
62 | on_error => sub { warn "FATAL: $_[0]"; exit 1 }, |
63 | on_error => sub { warn "ERROR: $_[0]"; exit 1 }, |
63 | on_event => sub { warn "$_[0] requests handled\n" }, |
64 | on_event => sub { warn "$_[0] requests handled\n" }, |
64 | on_destroy => $done, |
65 | on_destroy => $done, |
65 | ); |
66 | ); |
66 | |
67 | |
67 | for my $id (1..6) { |
68 | for my $id (1..6) { |
… | |
… | |
189 | so silly anymore. |
190 | so silly anymore. |
190 | |
191 | |
191 | Without further ado, here is the code: |
192 | Without further ado, here is the code: |
192 | |
193 | |
193 | use AnyEvent; |
194 | use AnyEvent; |
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195 | use AnyEvent::Fork; |
194 | use AnyEvent::Fork::RPC; |
196 | use AnyEvent::Fork::RPC; |
195 | |
197 | |
196 | my $done = AE::cv; |
198 | my $done = AE::cv; |
197 | |
199 | |
198 | my $rpc = AnyEvent::Fork |
200 | my $rpc = AnyEvent::Fork |
199 | ->new |
201 | ->new |
200 | ->require ("AnyEvent::Fork::RPC::Async") |
202 | ->require ("AnyEvent::Fork::RPC::Async") |
201 | ->eval (do { local $/; <DATA> }) |
203 | ->eval (do { local $/; <DATA> }) |
202 | ->AnyEvent::Fork::RPC::run ("run", |
204 | ->AnyEvent::Fork::RPC::run ("run", |
203 | async => 1, |
205 | async => 1, |
204 | on_error => sub { warn "FATAL: $_[0]"; exit 1 }, |
206 | on_error => sub { warn "ERROR: $_[0]"; exit 1 }, |
205 | on_event => sub { print $_[0] }, |
207 | on_event => sub { print $_[0] }, |
206 | on_destroy => $done, |
208 | on_destroy => $done, |
207 | ); |
209 | ); |
208 | |
210 | |
209 | for my $count (3, 2, 1) { |
211 | for my $count (3, 2, 1) { |
… | |
… | |
285 | |
287 | |
286 | This concludes the async example. Since L<AnyEvent::Fork> does not |
288 | This concludes the async example. Since L<AnyEvent::Fork> does not |
287 | actually fork, you are free to use about any module in the child, not just |
289 | actually fork, you are free to use about any module in the child, not just |
288 | L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example. |
290 | L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example. |
289 | |
291 | |
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292 | =head2 Example 3: Asynchronous backend with Coro |
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293 | |
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294 | With L<Coro> you can create a nice asynchronous backend implementation by |
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295 | defining an rpc server function that creates a new Coro thread for every |
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296 | request that calls a function "normally", i.e. the parameters from the |
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297 | parent process are passed to it, and any return values are returned to the |
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298 | parent process, e.g.: |
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299 | |
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300 | package My::Arith; |
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301 | |
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302 | sub add { |
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303 | return $_[0] + $_[1]; |
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304 | } |
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305 | |
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306 | sub mul { |
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307 | return $_[0] * $_[1]; |
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308 | } |
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309 | |
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310 | sub run { |
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311 | my ($done, $func, @arg) = @_; |
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312 | |
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313 | Coro::async_pool { |
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314 | $done->($func->(@arg)); |
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315 | }; |
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316 | } |
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317 | |
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318 | The C<run> function creates a new thread for every invocation, using the |
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319 | first argument as function name, and calls the C<$done> callback on it's |
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320 | return values. This makes it quite natural to define the C<add> and C<mul> |
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321 | functions to add or multiply two numbers and return the result. |
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322 | |
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323 | Since this is the asynchronous backend, it's quite possible to define RPC |
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324 | function that do I/O or wait for external events - their execution will |
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325 | overlap as needed. |
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326 | |
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327 | The above could be used like this: |
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328 | |
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329 | my $rpc = AnyEvent::Fork |
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330 | ->new |
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331 | ->require ("MyWorker") |
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332 | ->AnyEvent::Fork::RPC::run ("My::Arith::run", |
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333 | on_error => ..., on_event => ..., on_destroy => ..., |
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334 | ); |
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335 | |
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336 | $rpc->(add => 1, 3, Coro::rouse_cb); say Coro::rouse_wait; |
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337 | $rpc->(mul => 3, 2, Coro::rouse_cb); say Coro::rouse_wait; |
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338 | |
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339 | The C<say>'s will print C<4> and C<6>. |
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340 | |
290 | =head1 PARENT PROCESS USAGE |
341 | =head1 PARENT PROCESS USAGE |
291 | |
342 | |
292 | This module exports nothing, and only implements a single function: |
343 | This module exports nothing, and only implements a single function: |
293 | |
344 | |
294 | =over 4 |
345 | =over 4 |
… | |
… | |
301 | |
352 | |
302 | use Errno (); |
353 | use Errno (); |
303 | use Guard (); |
354 | use Guard (); |
304 | |
355 | |
305 | use AnyEvent; |
356 | use AnyEvent; |
306 | use AnyEvent::Fork; # we don't actually depend on it, this is for convenience |
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307 | |
357 | |
308 | our $VERSION = 0.1; |
358 | our $VERSION = 1.1; |
309 | |
359 | |
310 | =item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...] |
360 | =item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...] |
311 | |
361 | |
312 | The traditional way to call it. But it is way cooler to call it in the |
362 | The traditional way to call it. But it is way cooler to call it in the |
313 | following way: |
363 | following way: |
… | |
… | |
333 | Called on (fatal) errors, with a descriptive (hopefully) message. If |
383 | Called on (fatal) errors, with a descriptive (hopefully) message. If |
334 | this callback is not provided, but C<on_event> is, then the C<on_event> |
384 | this callback is not provided, but C<on_event> is, then the C<on_event> |
335 | callback is called with the first argument being the string C<error>, |
385 | callback is called with the first argument being the string C<error>, |
336 | followed by the error message. |
386 | followed by the error message. |
337 | |
387 | |
338 | If neither handler is provided it prints the error to STDERR and will |
388 | If neither handler is provided, then the error is reported with loglevel |
339 | start failing badly. |
389 | C<error> via C<AE::log>. |
340 | |
390 | |
341 | =item on_event => $cb->(...) |
391 | =item on_event => $cb->(...) |
342 | |
392 | |
343 | Called for every call to the C<AnyEvent::Fork::RPC::event> function in the |
393 | Called for every call to the C<AnyEvent::Fork::RPC::event> function in the |
344 | child, with the arguments of that function passed to the callback. |
394 | child, with the arguments of that function passed to the callback. |
… | |
… | |
372 | |
422 | |
373 | The default server used in the child does all I/O blockingly, and only |
423 | The default server used in the child does all I/O blockingly, and only |
374 | allows a single RPC call to execute concurrently. |
424 | allows a single RPC call to execute concurrently. |
375 | |
425 | |
376 | Setting C<async> to a true value switches to another implementation that |
426 | Setting C<async> to a true value switches to another implementation that |
377 | uses L<AnyEvent> in the child and allows multiple concurrent RPC calls. |
427 | uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it |
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428 | does not support recursion in the event loop however, blocking condvar |
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429 | calls will fail). |
378 | |
430 | |
379 | The actual API in the child is documented in the section that describes |
431 | The actual API in the child is documented in the section that describes |
380 | the calling semantics of the returned C<$rpc> function. |
432 | the calling semantics of the returned C<$rpc> function. |
381 | |
433 | |
382 | If you want to pre-load the actual back-end modules to enable memory |
434 | If you want to pre-load the actual back-end modules to enable memory |
… | |
… | |
384 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
436 | synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode. |
385 | |
437 | |
386 | If you use a template process and want to fork both sync and async |
438 | If you use a template process and want to fork both sync and async |
387 | children, then it is permissible to load both modules. |
439 | children, then it is permissible to load both modules. |
388 | |
440 | |
389 | =item serialiser => $string (default: '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })') |
441 | =item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER) |
390 | |
442 | |
391 | All arguments, result data and event data have to be serialised to be |
443 | All arguments, result data and event data have to be serialised to be |
392 | transferred between the processes. For this, they have to be frozen and |
444 | transferred between the processes. For this, they have to be frozen and |
393 | thawed in both parent and child processes. |
445 | thawed in both parent and child processes. |
394 | |
446 | |
395 | By default, only octet strings can be passed between the processes, which |
447 | By default, only octet strings can be passed between the processes, which |
396 | is reasonably fast and efficient. |
448 | is reasonably fast and efficient and requires no extra modules. |
397 | |
449 | |
398 | For more complicated use cases, you can provide your own freeze and thaw |
450 | For more complicated use cases, you can provide your own freeze and thaw |
399 | functions, by specifying a string with perl source code. It's supposed to |
451 | functions, by specifying a string with perl source code. It's supposed to |
400 | return two code references when evaluated: the first receives a list of |
452 | return two code references when evaluated: the first receives a list of |
401 | perl values and must return an octet string. The second receives the octet |
453 | perl values and must return an octet string. The second receives the octet |
… | |
… | |
403 | |
455 | |
404 | If you need an external module for serialisation, then you can either |
456 | If you need an external module for serialisation, then you can either |
405 | pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use> |
457 | pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use> |
406 | or C<require> statement into the serialiser string. Or both. |
458 | or C<require> statement into the serialiser string. Or both. |
407 | |
459 | |
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460 | Here are some examples - some of them are also available as global |
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461 | variables that make them easier to use. |
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462 | |
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463 | =over 4 |
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464 | |
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465 | =item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER> |
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466 | |
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467 | This serialiser concatenates length-prefixes octet strings, and is the |
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468 | default. That means you can only pass (and return) strings containing |
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469 | character codes 0-255. |
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470 | |
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471 | Implementation: |
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472 | |
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473 | ( |
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474 | sub { pack "(w/a*)*", @_ }, |
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475 | sub { unpack "(w/a*)*", shift } |
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476 | ) |
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477 | |
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478 | =item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER> |
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479 | |
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480 | This serialiser creates JSON arrays - you have to make sure the L<JSON> |
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481 | module is installed for this serialiser to work. It can be beneficial for |
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482 | sharing when you preload the L<JSON> module in a template process. |
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483 | |
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484 | L<JSON> (with L<JSON::XS> installed) is slower than the octet string |
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485 | serialiser, but usually much faster than L<Storable>, unless big chunks of |
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486 | binary data need to be transferred. |
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487 | |
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488 | Implementation: |
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489 | |
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490 | use JSON (); |
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491 | ( |
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492 | sub { JSON::encode_json \@_ }, |
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493 | sub { @{ JSON::decode_json shift } } |
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494 | ) |
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495 | |
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496 | =item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER> |
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497 | |
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498 | This serialiser uses L<Storable>, which means it has high chance of |
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499 | serialising just about anything you throw at it, at the cost of having |
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500 | very high overhead per operation. It also comes with perl. It should be |
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501 | used when you need to serialise complex data structures. |
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502 | |
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503 | Implementation: |
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504 | |
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505 | use Storable (); |
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506 | ( |
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507 | sub { Storable::freeze \@_ }, |
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508 | sub { @{ Storable::thaw shift } } |
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509 | ) |
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510 | |
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511 | =item portable storable - C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER> |
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512 | |
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513 | This serialiser also uses L<Storable>, but uses it's "network" format |
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514 | to serialise data, which makes it possible to talk to different |
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515 | perl binaries (for example, when talking to a process created with |
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516 | L<AnyEvent::Fork::Remote>). |
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517 | |
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518 | Implementation: |
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519 | |
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520 | use Storable (); |
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521 | ( |
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522 | sub { Storable::nfreeze \@_ }, |
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523 | sub { @{ Storable::thaw shift } } |
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524 | ) |
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525 | |
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526 | =back |
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527 | |
408 | =back |
528 | =back |
409 | |
529 | |
410 | See the examples section earlier in this document for some actual |
530 | See the examples section earlier in this document for some actual |
411 | examples. |
531 | examples. |
412 | |
532 | |
413 | =cut |
533 | =cut |
414 | |
534 | |
415 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
535 | our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; |
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536 | our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })'; |
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537 | our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })'; |
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538 | our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })'; |
416 | |
539 | |
417 | sub run { |
540 | sub run { |
418 | my ($self, $function, %arg) = @_; |
541 | my ($self, $function, %arg) = @_; |
419 | |
542 | |
420 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
543 | my $serialiser = delete $arg{serialiser} || $STRING_SERIALISER; |
… | |
… | |
423 | my $on_destroy = delete $arg{on_destroy}; |
546 | my $on_destroy = delete $arg{on_destroy}; |
424 | |
547 | |
425 | # default for on_error is to on_event, if specified |
548 | # default for on_error is to on_event, if specified |
426 | $on_error ||= $on_event |
549 | $on_error ||= $on_event |
427 | ? sub { $on_event->(error => shift) } |
550 | ? sub { $on_event->(error => shift) } |
428 | : sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" }; |
551 | : sub { AE::log die => "AnyEvent::Fork::RPC: uncaught error: $_[0]." }; |
429 | |
552 | |
430 | # default for on_event is to raise an error |
553 | # default for on_event is to raise an error |
431 | $on_event ||= sub { $on_error->("event received, but no on_event handler") }; |
554 | $on_event ||= sub { $on_error->("event received, but no on_event handler") }; |
432 | |
555 | |
433 | my ($f, $t) = eval $serialiser; die $@ if $@; |
556 | my ($f, $t) = eval $serialiser; die $@ if $@; |
… | |
… | |
465 | $rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf; |
588 | $rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf; |
466 | $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf; |
589 | $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf; |
467 | |
590 | |
468 | if ($len) { |
591 | if ($len) { |
469 | while (8 <= length $rbuf) { |
592 | while (8 <= length $rbuf) { |
470 | ($id, $len) = unpack "LL", $rbuf; |
593 | ($id, $len) = unpack "NN", $rbuf; |
471 | 8 + $len <= length $rbuf |
594 | 8 + $len <= length $rbuf |
472 | or last; |
595 | or last; |
473 | |
596 | |
474 | my @r = $t->(substr $rbuf, 8, $len); |
597 | my @r = $t->(substr $rbuf, 8, $len); |
475 | substr $rbuf, 0, 8 + $len, ""; |
598 | substr $rbuf, 0, 8 + $len, ""; |
… | |
… | |
489 | } |
612 | } |
490 | } elsif (defined $len) { |
613 | } elsif (defined $len) { |
491 | undef $rw; undef $ww; # it ends here |
614 | undef $rw; undef $ww; # it ends here |
492 | |
615 | |
493 | if (@rcb || %rcb) { |
616 | if (@rcb || %rcb) { |
494 | use Data::Dump;ddx[\@rcb,\%rcb];#d# |
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495 | $on_error->("unexpected eof"); |
617 | $on_error->("unexpected eof"); |
496 | } else { |
618 | } else { |
497 | $on_destroy->(); |
619 | $on_destroy->() |
|
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620 | if $on_destroy; |
498 | } |
621 | } |
499 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
622 | } elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) { |
500 | undef $rw; undef $ww; # it ends here |
623 | undef $rw; undef $ww; # it ends here |
501 | $on_error->("read: $!"); |
624 | $on_error->("read: $!"); |
502 | } |
625 | } |
… | |
… | |
505 | $ww ||= AE::io $fh, 1, $wcb; |
628 | $ww ||= AE::io $fh, 1, $wcb; |
506 | }); |
629 | }); |
507 | |
630 | |
508 | my $guard = Guard::guard { |
631 | my $guard = Guard::guard { |
509 | $shutdown = 1; |
632 | $shutdown = 1; |
510 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
633 | |
|
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634 | shutdown $fh, 1 if $fh && !$ww; |
511 | }; |
635 | }; |
512 | |
636 | |
513 | my $id; |
637 | my $id; |
514 | |
638 | |
515 | $arg{async} |
639 | $arg{async} |
… | |
… | |
517 | $id = ($id == 0xffffffff ? 0 : $id) + 1; |
641 | $id = ($id == 0xffffffff ? 0 : $id) + 1; |
518 | $id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops |
642 | $id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops |
519 | |
643 | |
520 | $rcb{$id} = pop; |
644 | $rcb{$id} = pop; |
521 | |
645 | |
522 | $guard; # keep it alive |
646 | $guard if 0; # keep it alive |
523 | |
647 | |
524 | $wbuf .= pack "LL/a*", $id, &$f; |
648 | $wbuf .= pack "NN/a*", $id, &$f; |
525 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
649 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
526 | } |
650 | } |
527 | : sub { |
651 | : sub { |
528 | push @rcb, pop; |
652 | push @rcb, pop; |
529 | |
653 | |
530 | $guard; # keep it alive |
654 | $guard; # keep it alive |
531 | |
655 | |
532 | $wbuf .= pack "L/a*", &$f; |
656 | $wbuf .= pack "N/a*", &$f; |
533 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
657 | $ww ||= $fh && AE::io $fh, 1, $wcb; |
534 | } |
658 | } |
535 | } |
659 | } |
536 | |
660 | |
537 | =item $rpc->(..., $cb->(...)) |
661 | =item $rpc->(..., $cb->(...)) |
… | |
… | |
579 | See the examples section earlier in this document for some actual |
703 | See the examples section earlier in this document for some actual |
580 | examples. |
704 | examples. |
581 | |
705 | |
582 | =back |
706 | =back |
583 | |
707 | |
|
|
708 | =head1 ADVANCED TOPICS |
|
|
709 | |
|
|
710 | =head2 Choosing a backend |
|
|
711 | |
|
|
712 | So how do you decide which backend to use? Well, that's your problem to |
|
|
713 | solve, but here are some thoughts on the matter: |
|
|
714 | |
|
|
715 | =over 4 |
|
|
716 | |
|
|
717 | =item Synchronous |
|
|
718 | |
|
|
719 | The synchronous backend does not rely on any external modules (well, |
|
|
720 | except L<common::sense>, which works around a bug in how perl's warning |
|
|
721 | system works). This keeps the process very small, for example, on my |
|
|
722 | system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB |
|
|
723 | after C<use warnings; use strict> (for people who grew up with C64s around |
|
|
724 | them this is probably shocking every single time they see it). The worker |
|
|
725 | process in the first example in this document uses 1792kB. |
|
|
726 | |
|
|
727 | Since the calls are done synchronously, slow jobs will keep newer jobs |
|
|
728 | from executing. |
|
|
729 | |
|
|
730 | The synchronous backend also has no overhead due to running an event loop |
|
|
731 | - reading requests is therefore very efficient, while writing responses is |
|
|
732 | less so, as every response results in a write syscall. |
|
|
733 | |
|
|
734 | If the parent process is busy and a bit slow reading responses, the child |
|
|
735 | waits instead of processing further requests. This also limits the amount |
|
|
736 | of memory needed for buffering, as never more than one response has to be |
|
|
737 | buffered. |
|
|
738 | |
|
|
739 | The API in the child is simple - you just have to define a function that |
|
|
740 | does something and returns something. |
|
|
741 | |
|
|
742 | It's hard to use modules or code that relies on an event loop, as the |
|
|
743 | child cannot execute anything while it waits for more input. |
|
|
744 | |
|
|
745 | =item Asynchronous |
|
|
746 | |
|
|
747 | The asynchronous backend relies on L<AnyEvent>, which tries to be small, |
|
|
748 | but still comes at a price: On my system, the worker from example 1a uses |
|
|
749 | 3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader> |
|
|
750 | which in turn loads a lot of other modules such as L<warnings>, L<strict>, |
|
|
751 | L<vars>, L<Exporter>...). |
|
|
752 | |
|
|
753 | It batches requests and responses reasonably efficiently, doing only as |
|
|
754 | few reads and writes as needed, but needs to poll for events via the event |
|
|
755 | loop. |
|
|
756 | |
|
|
757 | Responses are queued when the parent process is busy. This means the child |
|
|
758 | can continue to execute any queued requests. It also means that a child |
|
|
759 | might queue a lot of responses in memory when it generates them and the |
|
|
760 | parent process is slow accepting them. |
|
|
761 | |
|
|
762 | The API is not a straightforward RPC pattern - you have to call a |
|
|
763 | "done" callback to pass return values and signal completion. Also, more |
|
|
764 | importantly, the API starts jobs as fast as possible - when 1000 jobs |
|
|
765 | are queued and the jobs are slow, they will all run concurrently. The |
|
|
766 | child must implement some queueing/limiting mechanism if this causes |
|
|
767 | problems. Alternatively, the parent could limit the amount of rpc calls |
|
|
768 | that are outstanding. |
|
|
769 | |
|
|
770 | Blocking use of condvars is not supported. |
|
|
771 | |
|
|
772 | Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is |
|
|
773 | easy. |
|
|
774 | |
|
|
775 | =back |
|
|
776 | |
|
|
777 | =head2 Passing file descriptors |
|
|
778 | |
|
|
779 | Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file |
|
|
780 | descriptor passing abilities. |
|
|
781 | |
|
|
782 | The reason is that passing file descriptors is extraordinary tricky |
|
|
783 | business, and conflicts with efficient batching of messages. |
|
|
784 | |
|
|
785 | There still is a method you can use: Create a |
|
|
786 | C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to |
|
|
787 | the process before you pass control to C<AnyEvent::Fork::RPC::run>. |
|
|
788 | |
|
|
789 | Whenever you want to pass a file descriptor, send an rpc request to the |
|
|
790 | child process (so it expects the descriptor), then send it over the other |
|
|
791 | half of the socketpair. The child should fetch the descriptor from the |
|
|
792 | half it has passed earlier. |
|
|
793 | |
|
|
794 | Here is some (untested) pseudocode to that effect: |
|
|
795 | |
|
|
796 | use AnyEvent::Util; |
|
|
797 | use AnyEvent::Fork; |
|
|
798 | use AnyEvent::Fork::RPC; |
|
|
799 | use IO::FDPass; |
|
|
800 | |
|
|
801 | my ($s1, $s2) = AnyEvent::Util::portable_socketpair; |
|
|
802 | |
|
|
803 | my $rpc = AnyEvent::Fork |
|
|
804 | ->new |
|
|
805 | ->send_fh ($s2) |
|
|
806 | ->require ("MyWorker") |
|
|
807 | ->AnyEvent::Fork::RPC::run ("MyWorker::run" |
|
|
808 | init => "MyWorker::init", |
|
|
809 | ); |
|
|
810 | |
|
|
811 | undef $s2; # no need to keep it around |
|
|
812 | |
|
|
813 | # pass an fd |
|
|
814 | $rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv); |
|
|
815 | |
|
|
816 | IO::FDPass fileno $s1, fileno $handle_to_pass; |
|
|
817 | |
|
|
818 | $cv->recv; |
|
|
819 | |
|
|
820 | The MyWorker module could look like this: |
|
|
821 | |
|
|
822 | package MyWorker; |
|
|
823 | |
|
|
824 | use IO::FDPass; |
|
|
825 | |
|
|
826 | my $s2; |
|
|
827 | |
|
|
828 | sub init { |
|
|
829 | $s2 = $_[0]; |
|
|
830 | } |
|
|
831 | |
|
|
832 | sub run { |
|
|
833 | if ($_[0] eq "i'll send some fd now, please expect it!") { |
|
|
834 | my $fd = IO::FDPass::recv fileno $s2; |
|
|
835 | ... |
|
|
836 | } |
|
|
837 | } |
|
|
838 | |
|
|
839 | Of course, this might be blocking if you pass a lot of file descriptors, |
|
|
840 | so you might want to look into L<AnyEvent::FDpasser> which can handle the |
|
|
841 | gory details. |
|
|
842 | |
|
|
843 | =head1 EXCEPTIONS |
|
|
844 | |
|
|
845 | There are no provisions whatsoever for catching exceptions at this time - |
|
|
846 | in the child, exeptions might kill the process, causing calls to be lost |
|
|
847 | and the parent encountering a fatal error. In the parent, exceptions in |
|
|
848 | the result callback will not be caught and cause undefined behaviour. |
|
|
849 | |
584 | =head1 SEE ALSO |
850 | =head1 SEE ALSO |
585 | |
851 | |
586 | L<AnyEvent::Fork> (to create the processes in the first place), |
852 | L<AnyEvent::Fork>, to create the processes in the first place. |
|
|
853 | |
|
|
854 | L<AnyEvent::Fork::Remote>, likewise, but helpful for remote processes. |
|
|
855 | |
587 | L<AnyEvent::Fork::Pool> (to manage whole pools of processes). |
856 | L<AnyEvent::Fork::Pool>, to manage whole pools of processes. |
588 | |
857 | |
589 | =head1 AUTHOR AND CONTACT INFORMATION |
858 | =head1 AUTHOR AND CONTACT INFORMATION |
590 | |
859 | |
591 | Marc Lehmann <schmorp@schmorp.de> |
860 | Marc Lehmann <schmorp@schmorp.de> |
592 | http://software.schmorp.de/pkg/AnyEvent-Fork-RPC |
861 | http://software.schmorp.de/pkg/AnyEvent-Fork-RPC |