| 1 |
NAME |
| 2 |
AnyEvent - provide framework for multiple event loops |
| 3 |
|
| 4 |
Event, Coro, Glib, Tk, Perl - various supported event loops |
| 5 |
|
| 6 |
SYNOPSIS |
| 7 |
use AnyEvent; |
| 8 |
|
| 9 |
my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
| 10 |
... |
| 11 |
}); |
| 12 |
|
| 13 |
my $w = AnyEvent->timer (after => $seconds, cb => sub { |
| 14 |
... |
| 15 |
}); |
| 16 |
|
| 17 |
my $w = AnyEvent->condvar; # stores wether a condition was flagged |
| 18 |
$w->wait; # enters "main loop" till $condvar gets ->broadcast |
| 19 |
$w->broadcast; # wake up current and all future wait's |
| 20 |
|
| 21 |
DESCRIPTION |
| 22 |
AnyEvent provides an identical interface to multiple event loops. This |
| 23 |
allows module authors to utilise an event loop without forcing module |
| 24 |
users to use the same event loop (as only a single event loop can |
| 25 |
coexist peacefully at any one time). |
| 26 |
|
| 27 |
The interface itself is vaguely similar but not identical to the Event |
| 28 |
module. |
| 29 |
|
| 30 |
On the first call of any method, the module tries to detect the |
| 31 |
currently loaded event loop by probing wether any of the following |
| 32 |
modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is |
| 33 |
used. If none is found, the module tries to load these modules in the |
| 34 |
order given. The first one that could be successfully loaded will be |
| 35 |
used. If still none could be found, AnyEvent will fall back to a |
| 36 |
pure-perl event loop, which is also not very efficient. |
| 37 |
|
| 38 |
Because AnyEvent first checks for modules that are already loaded, |
| 39 |
loading an Event model explicitly before first using AnyEvent will |
| 40 |
likely make that model the default. For example: |
| 41 |
|
| 42 |
use Tk; |
| 43 |
use AnyEvent; |
| 44 |
|
| 45 |
# .. AnyEvent will likely default to Tk |
| 46 |
|
| 47 |
The pure-perl implementation of AnyEvent is called |
| 48 |
"AnyEvent::Impl::Perl". Like other event modules you can load it |
| 49 |
explicitly. |
| 50 |
|
| 51 |
WATCHERS |
| 52 |
AnyEvent has the central concept of a *watcher*, which is an object that |
| 53 |
stores relevant data for each kind of event you are waiting for, such as |
| 54 |
the callback to call, the filehandle to watch, etc. |
| 55 |
|
| 56 |
These watchers are normal Perl objects with normal Perl lifetime. After |
| 57 |
creating a watcher it will immediately "watch" for events and invoke the |
| 58 |
callback. To disable the watcher you have to destroy it (e.g. by setting |
| 59 |
the variable that stores it to "undef" or otherwise deleting all |
| 60 |
references to it). |
| 61 |
|
| 62 |
All watchers are created by calling a method on the "AnyEvent" class. |
| 63 |
|
| 64 |
IO WATCHERS |
| 65 |
You can create I/O watcher by calling the "AnyEvent->io" method with the |
| 66 |
following mandatory arguments: |
| 67 |
|
| 68 |
"fh" the Perl *filehandle* (not filedescriptor) to watch for events. |
| 69 |
"poll" must be a string that is either "r" or "w", that creates a |
| 70 |
watcher waiting for "r"eadable or "w"ritable events. "cb" teh callback |
| 71 |
to invoke everytime the filehandle becomes ready. |
| 72 |
|
| 73 |
Only one io watcher per "fh" and "poll" combination is allowed (i.e. on |
| 74 |
a socket you can have one r + one w, not any more (limitation comes from |
| 75 |
Tk - if you are sure you are not using Tk this limitation is gone). |
| 76 |
|
| 77 |
Filehandles will be kept alive, so as long as the watcher exists, the |
| 78 |
filehandle exists, too. |
| 79 |
|
| 80 |
Example: |
| 81 |
|
| 82 |
# wait for readability of STDIN, then read a line and disable the watcher |
| 83 |
my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
| 84 |
chomp (my $input = <STDIN>); |
| 85 |
warn "read: $input\n"; |
| 86 |
undef $w; |
| 87 |
}); |
| 88 |
|
| 89 |
TIME WATCHERS |
| 90 |
You can create a time watcher by calling the "AnyEvent->timer" method |
| 91 |
with the following mandatory arguments: |
| 92 |
|
| 93 |
"after" after how many seconds (fractions are supported) should the |
| 94 |
timer activate. "cb" the callback to invoke. |
| 95 |
|
| 96 |
The timer callback will be invoked at most once: if you want a repeating |
| 97 |
timer you have to create a new watcher (this is a limitation by both Tk |
| 98 |
and Glib). |
| 99 |
|
| 100 |
Example: |
| 101 |
|
| 102 |
# fire an event after 7.7 seconds |
| 103 |
my $w = AnyEvent->timer (after => 7.7, cb => sub { |
| 104 |
warn "timeout\n"; |
| 105 |
}); |
| 106 |
|
| 107 |
# to cancel the timer: |
| 108 |
undef $w |
| 109 |
|
| 110 |
CONDITION WATCHERS |
| 111 |
Condition watchers can be created by calling the "AnyEvent->condvar" |
| 112 |
method without any arguments. |
| 113 |
|
| 114 |
A condition watcher watches for a condition - precisely that the |
| 115 |
"->broadcast" method has been called. |
| 116 |
|
| 117 |
The watcher has only two methods: |
| 118 |
|
| 119 |
$cv->wait |
| 120 |
Wait (blocking if necessary) until the "->broadcast" method has been |
| 121 |
called on c<$cv>, while servicing other watchers normally. |
| 122 |
|
| 123 |
Not all event models support a blocking wait - some die in that |
| 124 |
case, so if you are using this from a module, never require a |
| 125 |
blocking wait, but let the caller decide wether the call will block |
| 126 |
or not (for example, by coupling condition variables with some kind |
| 127 |
of request results and supporting callbacks so the caller knows that |
| 128 |
getting the result will not block, while still suppporting blockign |
| 129 |
waits if the caller so desires). |
| 130 |
|
| 131 |
You can only wait once on a condition - additional calls will return |
| 132 |
immediately. |
| 133 |
|
| 134 |
$cv->broadcast |
| 135 |
Flag the condition as ready - a running "->wait" and all further |
| 136 |
calls to "wait" will return after this method has been called. If |
| 137 |
nobody is waiting the broadcast will be remembered.. |
| 138 |
|
| 139 |
Example: |
| 140 |
|
| 141 |
# wait till the result is ready |
| 142 |
my $result_ready = AnyEvent->condvar; |
| 143 |
|
| 144 |
# do something such as adding a timer |
| 145 |
# or socket watcher the calls $result_ready->broadcast |
| 146 |
# when the "result" is ready. |
| 147 |
|
| 148 |
$result_ready->wait; |
| 149 |
|
| 150 |
SIGNAL WATCHERS |
| 151 |
You can listen for signals using a signal watcher, "signal" is the |
| 152 |
signal *name* without any "SIG" prefix. Multiple signals events can be |
| 153 |
clumped together into one callback invocation, and callback invocation |
| 154 |
might or might not be asynchronous. |
| 155 |
|
| 156 |
These watchers might use %SIG, so programs overwriting those signals |
| 157 |
directly will likely not work correctly. |
| 158 |
|
| 159 |
Example: exit on SIGINT |
| 160 |
|
| 161 |
my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
| 162 |
|
| 163 |
CHILD PROCESS WATCHERS |
| 164 |
You can also listen for the status of a child process specified by the |
| 165 |
"pid" argument (or any child if the pid argument is 0). The watcher will |
| 166 |
trigger as often as status change for the child are received. This works |
| 167 |
by installing a signal handler for "SIGCHLD". The callback will be |
| 168 |
called with the pid and exit status (as returned by waitpid). |
| 169 |
|
| 170 |
Example: wait for pid 1333 |
| 171 |
|
| 172 |
my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); |
| 173 |
|
| 174 |
GLOBALS |
| 175 |
$AnyEvent::MODEL |
| 176 |
Contains "undef" until the first watcher is being created. Then it |
| 177 |
contains the event model that is being used, which is the name of |
| 178 |
the Perl class implementing the model. This class is usually one of |
| 179 |
the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
| 180 |
case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
| 181 |
|
| 182 |
The known classes so far are: |
| 183 |
|
| 184 |
AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
| 185 |
AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). |
| 186 |
AnyEvent::Impl::Coro based on Coro::Event, second best choice. |
| 187 |
AnyEvent::Impl::Event based on Event, also second best choice :) |
| 188 |
AnyEvent::Impl::Glib based on Glib, second-best choice. |
| 189 |
AnyEvent::Impl::Tk based on Tk, very bad choice. |
| 190 |
AnyEvent::Impl::Perl pure-perl implementation, inefficient. |
| 191 |
|
| 192 |
AnyEvent::detect |
| 193 |
Returns $AnyEvent::MODEL, forcing autodetection of the event model |
| 194 |
if necessary. You should only call this function right before you |
| 195 |
would have created an AnyEvent watcher anyway, that is, very late at |
| 196 |
runtime. |
| 197 |
|
| 198 |
WHAT TO DO IN A MODULE |
| 199 |
As a module author, you should "use AnyEvent" and call AnyEvent methods |
| 200 |
freely, but you should not load a specific event module or rely on it. |
| 201 |
|
| 202 |
Be careful when you create watchers in the module body - Anyevent will |
| 203 |
decide which event module to use as soon as the first method is called, |
| 204 |
so by calling AnyEvent in your module body you force the user of your |
| 205 |
module to load the event module first. |
| 206 |
|
| 207 |
WHAT TO DO IN THE MAIN PROGRAM |
| 208 |
There will always be a single main program - the only place that should |
| 209 |
dictate which event model to use. |
| 210 |
|
| 211 |
If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
| 212 |
do anything special and let AnyEvent decide which implementation to |
| 213 |
chose. |
| 214 |
|
| 215 |
If the main program relies on a specific event model (for example, in |
| 216 |
Gtk2 programs you have to rely on either Glib or Glib::Event), you |
| 217 |
should load it before loading AnyEvent or any module that uses it, |
| 218 |
generally, as early as possible. The reason is that modules might create |
| 219 |
watchers when they are loaded, and AnyEvent will decide on the event |
| 220 |
model to use as soon as it creates watchers, and it might chose the |
| 221 |
wrong one unless you load the correct one yourself. |
| 222 |
|
| 223 |
You can chose to use a rather inefficient pure-perl implementation by |
| 224 |
loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is |
| 225 |
generally better. |
| 226 |
|
| 227 |
SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
| 228 |
If you need to support another event library which isn't directly |
| 229 |
supported by AnyEvent, you can supply your own interface to it by |
| 230 |
pushing, before the first watcher gets created, the package name of the |
| 231 |
event module and the package name of the interface to use onto |
| 232 |
@AnyEvent::REGISTRY. You can do that before and even without loading |
| 233 |
AnyEvent. |
| 234 |
|
| 235 |
Example: |
| 236 |
|
| 237 |
push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
| 238 |
|
| 239 |
This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
| 240 |
package/class when it finds the "urxvt" package/module is loaded. When |
| 241 |
AnyEvent is loaded and asked to find a suitable event model, it will |
| 242 |
first check for the presence of urxvt. |
| 243 |
|
| 244 |
The class should provide implementations for all watcher types (see |
| 245 |
AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) |
| 246 |
and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to |
| 247 |
see the sources). |
| 248 |
|
| 249 |
The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the |
| 250 |
above line as-is. An interface isn't included in AnyEvent because it |
| 251 |
doesn't make sense outside the embedded interpreter inside |
| 252 |
*rxvt-unicode*, and it is updated and maintained as part of the |
| 253 |
*rxvt-unicode* distribution. |
| 254 |
|
| 255 |
*rxvt-unicode* also cheats a bit by not providing blocking access to |
| 256 |
condition variables: code blocking while waiting for a condition will |
| 257 |
"die". This still works with most modules/usages, and blocking calls |
| 258 |
must not be in an interactive application, so it makes sense. |
| 259 |
|
| 260 |
ENVIRONMENT VARIABLES |
| 261 |
The following environment variables are used by this module: |
| 262 |
|
| 263 |
"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event |
| 264 |
model gets used. |
| 265 |
|
| 266 |
EXAMPLE |
| 267 |
The following program uses an io watcher to read data from stdin, a |
| 268 |
timer to display a message once per second, and a condvar to exit the |
| 269 |
program when the user enters quit: |
| 270 |
|
| 271 |
use AnyEvent; |
| 272 |
|
| 273 |
my $cv = AnyEvent->condvar; |
| 274 |
|
| 275 |
my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
| 276 |
warn "io event <$_[0]>\n"; # will always output <r> |
| 277 |
chomp (my $input = <STDIN>); # read a line |
| 278 |
warn "read: $input\n"; # output what has been read |
| 279 |
$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
| 280 |
}); |
| 281 |
|
| 282 |
my $time_watcher; # can only be used once |
| 283 |
|
| 284 |
sub new_timer { |
| 285 |
$timer = AnyEvent->timer (after => 1, cb => sub { |
| 286 |
warn "timeout\n"; # print 'timeout' about every second |
| 287 |
&new_timer; # and restart the time |
| 288 |
}); |
| 289 |
} |
| 290 |
|
| 291 |
new_timer; # create first timer |
| 292 |
|
| 293 |
$cv->wait; # wait until user enters /^q/i |
| 294 |
|
| 295 |
REAL-WORLD EXAMPLE |
| 296 |
Consider the Net::FCP module. It features (among others) the following |
| 297 |
API calls, which are to freenet what HTTP GET requests are to http: |
| 298 |
|
| 299 |
my $data = $fcp->client_get ($url); # blocks |
| 300 |
|
| 301 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
| 302 |
$transaction->cb ( sub { ... } ); # set optional result callback |
| 303 |
my $data = $transaction->result; # possibly blocks |
| 304 |
|
| 305 |
The "client_get" method works like "LWP::Simple::get": it requests the |
| 306 |
given URL and waits till the data has arrived. It is defined to be: |
| 307 |
|
| 308 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
| 309 |
|
| 310 |
And in fact is automatically generated. This is the blocking API of |
| 311 |
Net::FCP, and it works as simple as in any other, similar, module. |
| 312 |
|
| 313 |
More complicated is "txn_client_get": It only creates a transaction |
| 314 |
(completion, result, ...) object and initiates the transaction. |
| 315 |
|
| 316 |
my $txn = bless { }, Net::FCP::Txn::; |
| 317 |
|
| 318 |
It also creates a condition variable that is used to signal the |
| 319 |
completion of the request: |
| 320 |
|
| 321 |
$txn->{finished} = AnyAvent->condvar; |
| 322 |
|
| 323 |
It then creates a socket in non-blocking mode. |
| 324 |
|
| 325 |
socket $txn->{fh}, ...; |
| 326 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
| 327 |
connect $txn->{fh}, ... |
| 328 |
and !$!{EWOULDBLOCK} |
| 329 |
and !$!{EINPROGRESS} |
| 330 |
and Carp::croak "unable to connect: $!\n"; |
| 331 |
|
| 332 |
Then it creates a write-watcher which gets called whenever an error |
| 333 |
occurs or the connection succeeds: |
| 334 |
|
| 335 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
| 336 |
|
| 337 |
And returns this transaction object. The "fh_ready_w" callback gets |
| 338 |
called as soon as the event loop detects that the socket is ready for |
| 339 |
writing. |
| 340 |
|
| 341 |
The "fh_ready_w" method makes the socket blocking again, writes the |
| 342 |
request data and replaces the watcher by a read watcher (waiting for |
| 343 |
reply data). The actual code is more complicated, but that doesn't |
| 344 |
matter for this example: |
| 345 |
|
| 346 |
fcntl $txn->{fh}, F_SETFL, 0; |
| 347 |
syswrite $txn->{fh}, $txn->{request} |
| 348 |
or die "connection or write error"; |
| 349 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
| 350 |
|
| 351 |
Again, "fh_ready_r" waits till all data has arrived, and then stores the |
| 352 |
result and signals any possible waiters that the request ahs finished: |
| 353 |
|
| 354 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
| 355 |
|
| 356 |
if (end-of-file or data complete) { |
| 357 |
$txn->{result} = $txn->{buf}; |
| 358 |
$txn->{finished}->broadcast; |
| 359 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
| 360 |
} |
| 361 |
|
| 362 |
The "result" method, finally, just waits for the finished signal (if the |
| 363 |
request was already finished, it doesn't wait, of course, and returns |
| 364 |
the data: |
| 365 |
|
| 366 |
$txn->{finished}->wait; |
| 367 |
return $txn->{result}; |
| 368 |
|
| 369 |
The actual code goes further and collects all errors ("die"s, |
| 370 |
exceptions) that occured during request processing. The "result" method |
| 371 |
detects wether an exception as thrown (it is stored inside the $txn |
| 372 |
object) and just throws the exception, which means connection errors and |
| 373 |
other problems get reported tot he code that tries to use the result, |
| 374 |
not in a random callback. |
| 375 |
|
| 376 |
All of this enables the following usage styles: |
| 377 |
|
| 378 |
1. Blocking: |
| 379 |
|
| 380 |
my $data = $fcp->client_get ($url); |
| 381 |
|
| 382 |
2. Blocking, but parallelizing: |
| 383 |
|
| 384 |
my @datas = map $_->result, |
| 385 |
map $fcp->txn_client_get ($_), |
| 386 |
@urls; |
| 387 |
|
| 388 |
Both blocking examples work without the module user having to know |
| 389 |
anything about events. |
| 390 |
|
| 391 |
3a. Event-based in a main program, using any support Event module: |
| 392 |
|
| 393 |
use Event; |
| 394 |
|
| 395 |
$fcp->txn_client_get ($url)->cb (sub { |
| 396 |
my $txn = shift; |
| 397 |
my $data = $txn->result; |
| 398 |
... |
| 399 |
}); |
| 400 |
|
| 401 |
Event::loop; |
| 402 |
|
| 403 |
3b. The module user could use AnyEvent, too: |
| 404 |
|
| 405 |
use AnyEvent; |
| 406 |
|
| 407 |
my $quit = AnyEvent->condvar; |
| 408 |
|
| 409 |
$fcp->txn_client_get ($url)->cb (sub { |
| 410 |
... |
| 411 |
$quit->broadcast; |
| 412 |
}); |
| 413 |
|
| 414 |
$quit->wait; |
| 415 |
|
| 416 |
SEE ALSO |
| 417 |
Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. |
| 418 |
|
| 419 |
Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, |
| 420 |
AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
| 421 |
|
| 422 |
Nontrivial usage example: Net::FCP. |
| 423 |
|
| 424 |
|
