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Revision 1.276 by root, Sun Aug 9 10:53:33 2009 UTC vs.
Revision 1.302 by root, Fri Dec 4 16:31:57 2009 UTC

363might affect timers and time-outs. 363might affect timers and time-outs.
364 364
365When this is the case, you can call this method, which will update the 365When this is the case, you can call this method, which will update the
366event loop's idea of "current time". 366event loop's idea of "current time".
367 367
368A typical example would be a script in a web server (e.g. C<mod_perl>) -
369when mod_perl executes the script, then the event loop will have the wrong
370idea about the "current time" (being potentially far in the past, when the
371script ran the last time). In that case you should arrange a call to C<<
372AnyEvent->now_update >> each time the web server process wakes up again
373(e.g. at the start of your script, or in a handler).
374
368Note that updating the time I<might> cause some events to be handled. 375Note that updating the time I<might> cause some events to be handled.
369 376
370=back 377=back
371 378
372=head2 SIGNAL WATCHERS 379=head2 SIGNAL WATCHERS
395correctly. 402correctly.
396 403
397Example: exit on SIGINT 404Example: exit on SIGINT
398 405
399 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); 406 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
407
408=head3 Restart Behaviour
409
410While restart behaviour is up to the event loop implementation, most will
411not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
412pure perl implementation).
413
414=head3 Safe/Unsafe Signals
415
416Perl signals can be either "safe" (synchronous to opcode handling) or
417"unsafe" (asynchronous) - the former might get delayed indefinitely, the
418latter might corrupt your memory.
419
420AnyEvent signal handlers are, in addition, synchronous to the event loop,
421i.e. they will not interrupt your running perl program but will only be
422called as part of the normal event handling (just like timer, I/O etc.
423callbacks, too).
400 424
401=head3 Signal Races, Delays and Workarounds 425=head3 Signal Races, Delays and Workarounds
402 426
403Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching 427Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
404callbacks to signals in a generic way, which is a pity, as you cannot 428callbacks to signals in a generic way, which is a pity, as you cannot
592 after => 1, 616 after => 1,
593 cb => sub { $result_ready->send }, 617 cb => sub { $result_ready->send },
594 ); 618 );
595 619
596 # this "blocks" (while handling events) till the callback 620 # this "blocks" (while handling events) till the callback
597 # calls -<send 621 # calls ->send
598 $result_ready->recv; 622 $result_ready->recv;
599 623
600Example: wait for a timer, but take advantage of the fact that condition 624Example: wait for a timer, but take advantage of the fact that condition
601variables are also callable directly. 625variables are also callable directly.
602 626
666one. For example, a function that pings many hosts in parallel might want 690one. For example, a function that pings many hosts in parallel might want
667to use a condition variable for the whole process. 691to use a condition variable for the whole process.
668 692
669Every call to C<< ->begin >> will increment a counter, and every call to 693Every call to C<< ->begin >> will increment a counter, and every call to
670C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end 694C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
671>>, the (last) callback passed to C<begin> will be executed. That callback 695>>, the (last) callback passed to C<begin> will be executed, passing the
672is I<supposed> to call C<< ->send >>, but that is not required. If no 696condvar as first argument. That callback is I<supposed> to call C<< ->send
673callback was set, C<send> will be called without any arguments. 697>>, but that is not required. If no group callback was set, C<send> will
698be called without any arguments.
674 699
675You can think of C<< $cv->send >> giving you an OR condition (one call 700You can think of C<< $cv->send >> giving you an OR condition (one call
676sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND 701sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
677condition (all C<begin> calls must be C<end>'ed before the condvar sends). 702condition (all C<begin> calls must be C<end>'ed before the condvar sends).
678 703
705begung can potentially be zero: 730begung can potentially be zero:
706 731
707 my $cv = AnyEvent->condvar; 732 my $cv = AnyEvent->condvar;
708 733
709 my %result; 734 my %result;
710 $cv->begin (sub { $cv->send (\%result) }); 735 $cv->begin (sub { shift->send (\%result) });
711 736
712 for my $host (@list_of_hosts) { 737 for my $host (@list_of_hosts) {
713 $cv->begin; 738 $cv->begin;
714 ping_host_then_call_callback $host, sub { 739 ping_host_then_call_callback $host, sub {
715 $result{$host} = ...; 740 $result{$host} = ...;
1105 1130
1106package AnyEvent; 1131package AnyEvent;
1107 1132
1108# basically a tuned-down version of common::sense 1133# basically a tuned-down version of common::sense
1109sub common_sense { 1134sub common_sense {
1110 # no warnings 1135 # from common:.sense 1.0
1111 ${^WARNING_BITS} ^= ${^WARNING_BITS}; 1136 ${^WARNING_BITS} = "\xfc\x3f\x33\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
1112 # use strict vars subs 1137 # use strict vars subs
1113 $^H |= 0x00000600; 1138 $^H |= 0x00000600;
1114} 1139}
1115 1140
1116BEGIN { AnyEvent::common_sense } 1141BEGIN { AnyEvent::common_sense }
1117 1142
1118use Carp (); 1143use Carp ();
1119 1144
1120our $VERSION = 4.92; 1145our $VERSION = '5.21';
1121our $MODEL; 1146our $MODEL;
1122 1147
1123our $AUTOLOAD; 1148our $AUTOLOAD;
1124our @ISA; 1149our @ISA;
1125 1150
1126our @REGISTRY; 1151our @REGISTRY;
1127
1128our $WIN32;
1129 1152
1130our $VERBOSE; 1153our $VERBOSE;
1131 1154
1132BEGIN { 1155BEGIN {
1133 eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }"; 1156 eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
1168 [Prima:: => AnyEvent::Impl::POE::], 1191 [Prima:: => AnyEvent::Impl::POE::],
1169 # IO::Async is just too broken - we would need workarounds for its 1192 # IO::Async is just too broken - we would need workarounds for its
1170 # byzantine signal and broken child handling, among others. 1193 # byzantine signal and broken child handling, among others.
1171 # IO::Async is rather hard to detect, as it doesn't have any 1194 # IO::Async is rather hard to detect, as it doesn't have any
1172 # obvious default class. 1195 # obvious default class.
1173# [0, IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program 1196 [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
1174# [0, IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program 1197 [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
1175# [0, IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program 1198 [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
1199 [AnyEvent::Impl::IOAsync:: => AnyEvent::Impl::IOAsync::], # requires special main program
1176); 1200);
1177 1201
1178our %method = map +($_ => 1), 1202our %method = map +($_ => 1),
1179 qw(io timer time now now_update signal child idle condvar one_event DESTROY); 1203 qw(io timer time now now_update signal child idle condvar one_event DESTROY);
1180 1204
1287 # we assume CLOEXEC is already set by perl in all important cases 1311 # we assume CLOEXEC is already set by perl in all important cases
1288 1312
1289 ($fh2, $rw) 1313 ($fh2, $rw)
1290} 1314}
1291 1315
1292############################################################################# 1316=head1 SIMPLIFIED AE API
1293# "new" API, currently only emulation of it 1317
1294############################################################################# 1318Starting with version 5.0, AnyEvent officially supports a second, much
1319simpler, API that is designed to reduce the calling, typing and memory
1320overhead.
1321
1322See the L<AE> manpage for details.
1323
1324=cut
1295 1325
1296package AE; 1326package AE;
1297 1327
1298our $VERSION = $AnyEvent::VERSION; 1328our $VERSION = $AnyEvent::VERSION;
1299 1329
1300sub io($$$) { 1330sub io($$$) {
1301 AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2]) 1331 AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
1302} 1332}
1303 1333
1304sub timer($$$) { 1334sub timer($$$) {
1305 AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2]); 1335 AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
1306} 1336}
1307 1337
1308sub signal($$) { 1338sub signal($$) {
1309 AnyEvent->signal (signal => $_[0], cb => $_[1]); 1339 AnyEvent->signal (signal => $_[0], cb => $_[1])
1310} 1340}
1311 1341
1312sub child($$) { 1342sub child($$) {
1313 AnyEvent->child (pid => $_[0], cb => $_[1]); 1343 AnyEvent->child (pid => $_[0], cb => $_[1])
1314} 1344}
1315 1345
1316sub idle($) { 1346sub idle($) {
1317 AnyEvent->idle (cb => $_[0]); 1347 AnyEvent->idle (cb => $_[0])
1318} 1348}
1319 1349
1320sub cv(;&) { 1350sub cv(;&) {
1321 AnyEvent->condvar (@_ ? (cb => $_[0]) : ()) 1351 AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
1322} 1352}
1335 1365
1336package AnyEvent::Base; 1366package AnyEvent::Base;
1337 1367
1338# default implementations for many methods 1368# default implementations for many methods
1339 1369
1340sub _time { 1370sub _time() {
1341 # probe for availability of Time::HiRes 1371 # probe for availability of Time::HiRes
1342 if (eval "use Time::HiRes (); Time::HiRes::time (); 1") { 1372 if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
1343 warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8; 1373 warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
1344 *_time = \&Time::HiRes::time; 1374 *_time = \&Time::HiRes::time;
1345 # if (eval "use POSIX (); (POSIX::times())... 1375 # if (eval "use POSIX (); (POSIX::times())...
1365 1395
1366our $HAVE_ASYNC_INTERRUPT; 1396our $HAVE_ASYNC_INTERRUPT;
1367 1397
1368sub _have_async_interrupt() { 1398sub _have_async_interrupt() {
1369 $HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT} 1399 $HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
1370 && eval "use Async::Interrupt 1.0 (); 1") 1400 && eval "use Async::Interrupt 1.02 (); 1")
1371 unless defined $HAVE_ASYNC_INTERRUPT; 1401 unless defined $HAVE_ASYNC_INTERRUPT;
1372 1402
1373 $HAVE_ASYNC_INTERRUPT 1403 $HAVE_ASYNC_INTERRUPT
1374} 1404}
1375 1405
1378our ($SIG_COUNT, $SIG_TW); 1408our ($SIG_COUNT, $SIG_TW);
1379 1409
1380sub _signal_exec { 1410sub _signal_exec {
1381 $HAVE_ASYNC_INTERRUPT 1411 $HAVE_ASYNC_INTERRUPT
1382 ? $SIGPIPE_R->drain 1412 ? $SIGPIPE_R->drain
1383 : sysread $SIGPIPE_R, my $dummy, 9; 1413 : sysread $SIGPIPE_R, (my $dummy), 9;
1384 1414
1385 while (%SIG_EV) { 1415 while (%SIG_EV) {
1386 for (keys %SIG_EV) { 1416 for (keys %SIG_EV) {
1387 delete $SIG_EV{$_}; 1417 delete $SIG_EV{$_};
1388 $_->() for values %{ $SIG_CB{$_} || {} }; 1418 $_->() for values %{ $SIG_CB{$_} || {} };
1904 warn "read: $input\n"; # output what has been read 1934 warn "read: $input\n"; # output what has been read
1905 $cv->send if $input =~ /^q/i; # quit program if /^q/i 1935 $cv->send if $input =~ /^q/i; # quit program if /^q/i
1906 }, 1936 },
1907 ); 1937 );
1908 1938
1909 my $time_watcher; # can only be used once
1910
1911 sub new_timer {
1912 $timer = AnyEvent->timer (after => 1, cb => sub { 1939 my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1913 warn "timeout\n"; # print 'timeout' about every second 1940 warn "timeout\n"; # print 'timeout' at most every second
1914 &new_timer; # and restart the time
1915 }); 1941 });
1916 }
1917
1918 new_timer; # create first timer
1919 1942
1920 $cv->recv; # wait until user enters /^q/i 1943 $cv->recv; # wait until user enters /^q/i
1921 1944
1922=head1 REAL-WORLD EXAMPLE 1945=head1 REAL-WORLD EXAMPLE
1923 1946
2054through AnyEvent. The benchmark creates a lot of timers (with a zero 2077through AnyEvent. The benchmark creates a lot of timers (with a zero
2055timeout) and I/O watchers (watching STDOUT, a pty, to become writable, 2078timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
2056which it is), lets them fire exactly once and destroys them again. 2079which it is), lets them fire exactly once and destroys them again.
2057 2080
2058Source code for this benchmark is found as F<eg/bench> in the AnyEvent 2081Source code for this benchmark is found as F<eg/bench> in the AnyEvent
2059distribution. 2082distribution. It uses the L<AE> interface, which makes a real difference
2083for the EV and Perl backends only.
2060 2084
2061=head3 Explanation of the columns 2085=head3 Explanation of the columns
2062 2086
2063I<watcher> is the number of event watchers created/destroyed. Since 2087I<watcher> is the number of event watchers created/destroyed. Since
2064different event models feature vastly different performances, each event 2088different event models feature vastly different performances, each event
2085watcher. 2109watcher.
2086 2110
2087=head3 Results 2111=head3 Results
2088 2112
2089 name watchers bytes create invoke destroy comment 2113 name watchers bytes create invoke destroy comment
2090 EV/EV 400000 224 0.47 0.35 0.27 EV native interface 2114 EV/EV 100000 223 0.47 0.43 0.27 EV native interface
2091 EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers 2115 EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
2092 CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal 2116 Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
2093 Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation 2117 Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
2094 Event/Event 16000 517 32.20 31.80 0.81 Event native interface 2118 Event/Event 16000 516 31.16 31.84 0.82 Event native interface
2095 Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers 2119 Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
2096 IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll 2120 IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
2097 IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll 2121 IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
2098 Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour 2122 Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
2099 Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers 2123 Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
2100 POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event 2124 POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
2101 POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select 2125 POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
2102 2126
2103=head3 Discussion 2127=head3 Discussion
2104 2128
2105The benchmark does I<not> measure scalability of the event loop very 2129The benchmark does I<not> measure scalability of the event loop very
2106well. For example, a select-based event loop (such as the pure perl one) 2130well. For example, a select-based event loop (such as the pure perl one)
2118benchmark machine, handling an event takes roughly 1600 CPU cycles with 2142benchmark machine, handling an event takes roughly 1600 CPU cycles with
2119EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU 2143EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
2120cycles with POE. 2144cycles with POE.
2121 2145
2122C<EV> is the sole leader regarding speed and memory use, which are both 2146C<EV> is the sole leader regarding speed and memory use, which are both
2123maximal/minimal, respectively. Even when going through AnyEvent, it uses 2147maximal/minimal, respectively. When using the L<AE> API there is zero
2148overhead (when going through the AnyEvent API create is about 5-6 times
2149slower, with other times being equal, so still uses far less memory than
2124far less memory than any other event loop and is still faster than Event 2150any other event loop and is still faster than Event natively).
2125natively.
2126 2151
2127The pure perl implementation is hit in a few sweet spots (both the 2152The pure perl implementation is hit in a few sweet spots (both the
2128constant timeout and the use of a single fd hit optimisations in the perl 2153constant timeout and the use of a single fd hit optimisations in the perl
2129interpreter and the backend itself). Nevertheless this shows that it 2154interpreter and the backend itself). Nevertheless this shows that it
2130adds very little overhead in itself. Like any select-based backend its 2155adds very little overhead in itself. Like any select-based backend its
2204In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100 2229In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
2205(1%) are active. This mirrors the activity of large servers with many 2230(1%) are active. This mirrors the activity of large servers with many
2206connections, most of which are idle at any one point in time. 2231connections, most of which are idle at any one point in time.
2207 2232
2208Source code for this benchmark is found as F<eg/bench2> in the AnyEvent 2233Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
2209distribution. 2234distribution. It uses the L<AE> interface, which makes a real difference
2235for the EV and Perl backends only.
2210 2236
2211=head3 Explanation of the columns 2237=head3 Explanation of the columns
2212 2238
2213I<sockets> is the number of sockets, and twice the number of "servers" (as 2239I<sockets> is the number of sockets, and twice the number of "servers" (as
2214each server has a read and write socket end). 2240each server has a read and write socket end).
2222a new one that moves the timeout into the future. 2248a new one that moves the timeout into the future.
2223 2249
2224=head3 Results 2250=head3 Results
2225 2251
2226 name sockets create request 2252 name sockets create request
2227 EV 20000 69.01 11.16 2253 EV 20000 62.66 7.99
2228 Perl 20000 73.32 35.87 2254 Perl 20000 68.32 32.64
2229 IOAsync 20000 157.00 98.14 epoll 2255 IOAsync 20000 174.06 101.15 epoll
2230 IOAsync 20000 159.31 616.06 poll 2256 IOAsync 20000 174.67 610.84 poll
2231 Event 20000 212.62 257.32 2257 Event 20000 202.69 242.91
2232 Glib 20000 651.16 1896.30 2258 Glib 20000 557.01 1689.52
2233 POE 20000 349.67 12317.24 uses POE::Loop::Event 2259 POE 20000 341.54 12086.32 uses POE::Loop::Event
2234 2260
2235=head3 Discussion 2261=head3 Discussion
2236 2262
2237This benchmark I<does> measure scalability and overall performance of the 2263This benchmark I<does> measure scalability and overall performance of the
2238particular event loop. 2264particular event loop.
2364As you can see, the AnyEvent + EV combination even beats the 2390As you can see, the AnyEvent + EV combination even beats the
2365hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl 2391hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
2366backend easily beats IO::Lambda and POE. 2392backend easily beats IO::Lambda and POE.
2367 2393
2368And even the 100% non-blocking version written using the high-level (and 2394And even the 100% non-blocking version written using the high-level (and
2369slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a 2395slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
2370large margin, even though it does all of DNS, tcp-connect and socket I/O 2396higher level ("unoptimised") abstractions by a large margin, even though
2371in a non-blocking way. 2397it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
2372 2398
2373The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and 2399The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
2374F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are 2400F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
2375part of the IO::lambda distribution and were used without any changes. 2401part of the IO::Lambda distribution and were used without any changes.
2376 2402
2377 2403
2378=head1 SIGNALS 2404=head1 SIGNALS
2379 2405
2380AnyEvent currently installs handlers for these signals: 2406AnyEvent currently installs handlers for these signals:
2422it's built-in modules) are required to use it. 2448it's built-in modules) are required to use it.
2423 2449
2424That does not mean that AnyEvent won't take advantage of some additional 2450That does not mean that AnyEvent won't take advantage of some additional
2425modules if they are installed. 2451modules if they are installed.
2426 2452
2427This section epxlains which additional modules will be used, and how they 2453This section explains which additional modules will be used, and how they
2428affect AnyEvent's operetion. 2454affect AnyEvent's operation.
2429 2455
2430=over 4 2456=over 4
2431 2457
2432=item L<Async::Interrupt> 2458=item L<Async::Interrupt>
2433 2459
2438catch the signals) with some delay (default is 10 seconds, look for 2464catch the signals) with some delay (default is 10 seconds, look for
2439C<$AnyEvent::MAX_SIGNAL_LATENCY>). 2465C<$AnyEvent::MAX_SIGNAL_LATENCY>).
2440 2466
2441If this module is available, then it will be used to implement signal 2467If this module is available, then it will be used to implement signal
2442catching, which means that signals will not be delayed, and the event loop 2468catching, which means that signals will not be delayed, and the event loop
2443will not be interrupted regularly, which is more efficient (And good for 2469will not be interrupted regularly, which is more efficient (and good for
2444battery life on laptops). 2470battery life on laptops).
2445 2471
2446This affects not just the pure-perl event loop, but also other event loops 2472This affects not just the pure-perl event loop, but also other event loops
2447that have no signal handling on their own (e.g. Glib, Tk, Qt). 2473that have no signal handling on their own (e.g. Glib, Tk, Qt).
2448 2474
2469lot less memory), but otherwise doesn't affect guard operation much. It is 2495lot less memory), but otherwise doesn't affect guard operation much. It is
2470purely used for performance. 2496purely used for performance.
2471 2497
2472=item L<JSON> and L<JSON::XS> 2498=item L<JSON> and L<JSON::XS>
2473 2499
2474This module is required when you want to read or write JSON data via 2500One of these modules is required when you want to read or write JSON data
2475L<AnyEvent::Handle>. It is also written in pure-perl, but can take 2501via L<AnyEvent::Handle>. It is also written in pure-perl, but can take
2476advantage of the ultra-high-speed L<JSON::XS> module when it is installed. 2502advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
2477 2503
2478In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is 2504In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
2479installed. 2505installed.
2480 2506
2498 2524
2499Most event libraries are not fork-safe. The ones who are usually are 2525Most event libraries are not fork-safe. The ones who are usually are
2500because they rely on inefficient but fork-safe C<select> or C<poll> 2526because they rely on inefficient but fork-safe C<select> or C<poll>
2501calls. Only L<EV> is fully fork-aware. 2527calls. Only L<EV> is fully fork-aware.
2502 2528
2529This means that, in general, you cannot fork and do event processing
2530in the child if a watcher was created before the fork (which in turn
2531initialises the event library).
2532
2503If you have to fork, you must either do so I<before> creating your first 2533If you have to fork, you must either do so I<before> creating your first
2504watcher OR you must not use AnyEvent at all in the child OR you must do 2534watcher OR you must not use AnyEvent at all in the child OR you must do
2505something completely out of the scope of AnyEvent. 2535something completely out of the scope of AnyEvent.
2536
2537The problem of doing event processing in the parent I<and> the child
2538is much more complicated: even for backends that I<are> fork-aware or
2539fork-safe, their behaviour is not usually what you want: fork clones all
2540watchers, that means all timers, I/O watchers etc. are active in both
2541parent and child, which is almost never what you want.
2506 2542
2507 2543
2508=head1 SECURITY CONSIDERATIONS 2544=head1 SECURITY CONSIDERATIONS
2509 2545
2510AnyEvent can be forced to load any event model via 2546AnyEvent can be forced to load any event model via

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