NAME¶
EV - perl interface to libev, a high performance full-featured event loop
SYNOPSIS¶
use EV;
# TIMERS
my $w = EV::timer 2, 0, sub {
warn "is called after 2s";
};
my $w = EV::timer 2, 2, sub {
warn "is called roughly every 2s (repeat = 2)";
};
undef $w; # destroy event watcher again
my $w = EV::periodic 0, 60, 0, sub {
warn "is called every minute, on the minute, exactly";
};
# IO
my $w = EV::io *STDIN, EV::READ, sub {
my ($w, $revents) = @_; # all callbacks receive the watcher and event mask
warn "stdin is readable, you entered: ", <STDIN>;
};
# SIGNALS
my $w = EV::signal 'QUIT', sub {
warn "sigquit received\n";
};
# CHILD/PID STATUS CHANGES
my $w = EV::child 666, 0, sub {
my ($w, $revents) = @_;
my $status = $w->rstatus;
};
# STAT CHANGES
my $w = EV::stat "/etc/passwd", 10, sub {
my ($w, $revents) = @_;
warn $w->path, " has changed somehow.\n";
};
# MAINLOOP
EV::run; # loop until EV::unloop is called or all watchers stop
EV::run EV::RUN_ONCE; # block until at least one event could be handled
EV::run EV::RUN_NOWAIT; # try to handle same events, but do not block
BEFORE YOU START USING THIS MODULE¶
If you only need timer, I/O, signal, child and idle watchers and not the
advanced functionality of this module, consider using AnyEvent instead,
specifically the simplified API described in AE.
When used with EV as backend, the AE API is as fast as the native EV API, but
your programs/modules will still run with many other event loops.
DESCRIPTION¶
This module provides an interface to libev
(<
http://software.schmorp.de/pkg/libev.html>). While the documentation
below is comprehensive, one might also consult the documentation of libev
itself (<
http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod> or
perldoc EV::libev) for more subtle details on watcher semantics or some
discussion on the available backends, or how to force a specific backend with
"LIBEV_FLAGS", or just about in any case because it has much more
detailed information.
This module is very fast and scalable. It is actually so fast that you can use
it through the AnyEvent module, stay portable to other event loops (if you
don't rely on any watcher types not available through it) and still be faster
than with any other event loop currently supported in Perl.
PORTING FROM EV 3.X to 4.X¶
EV version 4 introduces a number of incompatible changes summarised here.
According to the depreciation strategy used by libev, there is a compatibility
layer in place so programs should continue to run unchanged (the XS interface
lacks this layer, so programs using that one need to be updated).
This compatibility layer will be switched off in some future release.
All changes relevant to Perl are renames of symbols, functions and methods:
EV::loop => EV::run
EV::LOOP_NONBLOCK => EV::RUN_NOWAIT
EV::LOOP_ONESHOT => EV::RUN_ONCE
EV::unloop => EV::break
EV::UNLOOP_CANCEL => EV::BREAK_CANCEL
EV::UNLOOP_ONE => EV::BREAK_ONE
EV::UNLOOP_ALL => EV::BREAK_ALL
EV::TIMEOUT => EV::TIMER
EV::loop_count => EV::iteration
EV::loop_depth => EV::depth
EV::loop_verify => EV::verify
The loop object methods corresponding to the functions above have been similarly
renamed.
MODULE EXPORTS¶
This module does not export any symbols.
EVENT LOOPS¶
EV supports multiple event loops: There is a single "default event
loop" that can handle everything including signals and child watchers,
and any number of "dynamic event loops" that can use different
backends (with various limitations), but no child and signal watchers.
You do not have to do anything to create the default event loop: When the module
is loaded a suitable backend is selected on the premise of selecting a working
backend (which for example rules out kqueue on most BSDs). Modules should,
unless they have "special needs" always use the default loop as this
is fastest (perl-wise), best supported by other modules (e.g. AnyEvent or
Coro) and most portable event loop.
For specific programs you can create additional event loops dynamically.
If you want to take advantage of kqueue (which often works properly for sockets
only) even though the default loop doesn't enable it, you can
embed a
kqueue loop into the default loop: running the default loop will then also
service the kqueue loop to some extent. See the example in the section about
embed watchers for an example on how to achieve that.
- $loop = new EV::Loop [$flags]
- Create a new event loop as per the specified flags. Please refer to the
"ev_loop_new ()" function description in the libev documentation
(<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#GLOBAL_FUNCTIONS>,
or locally-installed as EV::libev manpage) for more info.
The loop will automatically be destroyed when it is no longer referenced by
any watcher and the loop object goes out of scope.
If you are not embedding the loop, then Using "EV::FLAG_FORKCHECK"
is recommended, as only the default event loop is protected by this
module. If you are embedding this loop in the default loop, this is
not necessary, as "EV::embed" automatically does the right thing
on fork.
- $loop->loop_fork
- Must be called after a fork in the child, before entering or continuing
the event loop. An alternative is to use "EV::FLAG_FORKCHECK"
which calls this function automatically, at some performance loss (refer
to the libev documentation).
- $loop->verify
- Calls "ev_verify" to make internal consistency checks (for
debugging libev) and abort the program if any data structures were found
to be corrupted.
- $loop = EV::default_loop [$flags]
- Return the default loop (which is a singleton object). Since this module
already creates the default loop with default flags, specifying flags here
will not have any effect unless you destroy the default loop first, which
isn't supported. So in short: don't do it, and if you break it, you get to
keep the pieces.
BASIC INTERFACE¶
- $EV::DIED
- Must contain a reference to a function that is called when a callback
throws an exception (with $@ containing the error). The default prints an
informative message and continues.
If this callback throws an exception it will be silently ignored.
- $flags = EV::supported_backends
- $flags = EV::recommended_backends
- $flags = EV::embeddable_backends
- Returns the set (see "EV::BACKEND_*" flags) of backends
supported by this instance of EV, the set of recommended backends
(supposed to be good) for this platform and the set of embeddable backends
(see EMBED WATCHERS).
- EV::sleep $seconds
- Block the process for the given number of (fractional) seconds.
- $time = EV::time
- Returns the current time in (fractional) seconds since the epoch.
- $time = EV::now
- $time = $loop->now
- Returns the time the last event loop iteration has been started. This is
the time that (relative) timers are based on, and referring to it is
usually faster then calling EV::time.
- EV::now_update
- $loop->now_update
- Establishes the current time by querying the kernel, updating the time
returned by "EV::now" in the progress. This is a costly
operation and is usually done automatically within "EV::loop".
This function is rarely useful, but when some event callback runs for a very
long time without entering the event loop, updating libev's idea of the
current time is a good idea.
- EV::suspend
- $loop->suspend
- EV::resume
- $loop->resume
- These two functions suspend and resume a loop, for use when the loop is
not used for a while and timeouts should not be processed.
A typical use case would be an interactive program such as a game: When the
user presses "^Z" to suspend the game and resumes it an hour
later it would be best to handle timeouts as if no time had actually
passed while the program was suspended. This can be achieved by calling
"suspend" in your "SIGTSTP" handler, sending yourself
a "SIGSTOP" and calling "resume" directly afterwards
to resume timer processing.
Effectively, all "timer" watchers will be delayed by the time
spend between "suspend" and "resume", and all
"periodic" watchers will be rescheduled (that is, they will lose
any events that would have occured while suspended).
After calling "suspend" you must not call any
function on the given loop other than "resume", and you must
not call "resume" without a previous call to
"suspend".
Calling "suspend"/"resume" has the side effect of
updating the event loop time (see "now_update").
- $backend = EV::backend
- $backend = $loop->backend
- Returns an integer describing the backend used by libev
(EV::BACKEND_SELECT or EV::BACKEND_EPOLL).
- $active = EV::run [$flags]
- $active = $loop->run ([$flags])
- Begin checking for events and calling callbacks. It returns when a
callback calls EV::unloop or the flasg are nonzero (in which case the
return value is true) or when there are no active watchers which reference
the loop (keepalive is true), in which case the return value will be
false. The returnv alue can generally be interpreted as "if true,
there is more work left to do".
The $flags argument can be one of the following:
0 as above
EV::RUN_ONCE block at most once (wait, but do not loop)
EV::RUN_NOWAIT do not block at all (fetch/handle events but do not wait)
- EV::break [$how]
- $loop->break ([$how])
- When called with no arguments or an argument of EV::BREAK_ONE, makes the
innermost call to EV::loop return.
When called with an argument of EV::BREAK_ALL, all calls to EV::loop will
return as fast as possible.
When called with an argument of EV::BREAK_CANCEL, any pending break will be
cancelled.
- $count = EV::iteration
- $count = $loop->iteration
- Return the number of times the event loop has polled for new events.
Sometimes useful as a generation counter.
- EV::once $fh_or_undef, $events, $timeout, $cb->($revents)
- $loop->once ($fh_or_undef, $events, $timeout, $cb->($revents))
- This function rolls together an I/O and a timer watcher for a single
one-shot event without the need for managing a watcher object.
If $fh_or_undef is a filehandle or file descriptor, then $events must be a
bitset containing either "EV::READ", "EV::WRITE" or
"EV::READ | EV::WRITE", indicating the type of I/O event you
want to wait for. If you do not want to wait for some I/O event, specify
"undef" for $fh_or_undef and 0 for $events).
If timeout is "undef" or negative, then there will be no timeout.
Otherwise a EV::timer with this value will be started.
When an error occurs or either the timeout or I/O watcher triggers, then the
callback will be called with the received event set (in general you can
expect it to be a combination of "EV::ERROR",
"EV::READ", "EV::WRITE" and "EV::TIMER").
EV::once doesn't return anything: the watchers stay active till either of
them triggers, then they will be stopped and freed, and the callback
invoked.
- EV::feed_fd_event $fd, $revents
- $loop->feed_fd_event ($fd, $revents)
- Feed an event on a file descriptor into EV. EV will react to this call as
if the readyness notifications specified by $revents (a combination of
"EV::READ" and "EV::WRITE") happened on the file
descriptor $fd.
- EV::feed_signal_event $signal
- Feed a signal event into the default loop. EV will react to this call as
if the signal specified by $signal had occured.
- EV::feed_signal $signal
- Feed a signal event into EV - unlike "EV::feed_signal_event",
this works regardless of which loop has registered the signal, and is
mainly useful fro custom signal implementations.
- EV::set_io_collect_interval $time
- $loop->set_io_collect_interval ($time)
- EV::set_timeout_collect_interval $time
- $loop->set_timeout_collect_interval ($time)
- These advanced functions set the minimum block interval when polling for
I/O events and the minimum wait interval for timer events. See the libev
documentation at
<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP>
(locally installed as EV::libev) for a more detailed
discussion.
- $count = EV::pending_count
- $count = $loop->pending_count
- Returns the number of currently pending watchers.
- EV::invoke_pending
- $loop->invoke_pending
- Invoke all currently pending watchers.
WATCHER OBJECTS¶
A watcher is an object that gets created to record your interest in some event.
For instance, if you want to wait for STDIN to become readable, you would
create an EV::io watcher for that:
my $watcher = EV::io *STDIN, EV::READ, sub {
my ($watcher, $revents) = @_;
warn "yeah, STDIN should now be readable without blocking!\n"
};
All watchers can be active (waiting for events) or inactive (paused). Only
active watchers will have their callbacks invoked. All callbacks will be
called with at least two arguments: the watcher and a bitmask of received
events.
Each watcher type has its associated bit in revents, so you can use the same
callback for multiple watchers. The event mask is named after the type, i.e.
EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE, EV::periodic sets
EV::PERIODIC and so on, with the exception of I/O events (which can set both
EV::READ and EV::WRITE bits).
In the rare case where one wants to create a watcher but not start it at the
same time, each constructor has a variant with a trailing "_ns" in
its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.
Please note that a watcher will automatically be stopped when the watcher object
is destroyed, so you
need to keep the watcher objects returned by the
constructors.
Also, all methods changing some aspect of a watcher (->set, ->priority,
->fh and so on) automatically stop and start it again if it is active,
which means pending events get lost.
COMMON WATCHER METHODS¶
This section lists methods common to all watchers.
- $w->start
- Starts a watcher if it isn't active already. Does nothing to an already
active watcher. By default, all watchers start out in the active state
(see the description of the "_ns" variants if you need stopped
watchers).
- $w->stop
- Stop a watcher if it is active. Also clear any pending events (events that
have been received but that didn't yet result in a callback invocation),
regardless of whether the watcher was active or not.
- $bool = $w->is_active
- Returns true if the watcher is active, false otherwise.
- $current_data = $w->data
- $old_data = $w->data ($new_data)
- Queries a freely usable data scalar on the watcher and optionally changes
it. This is a way to associate custom data with a watcher:
my $w = EV::timer 60, 0, sub {
warn $_[0]->data;
};
$w->data ("print me!");
- $current_cb = $w->cb
- $old_cb = $w->cb ($new_cb)
- Queries the callback on the watcher and optionally changes it. You can do
this at any time without the watcher restarting.
- $current_priority = $w->priority
- $old_priority = $w->priority ($new_priority)
- Queries the priority on the watcher and optionally changes it. Pending
watchers with higher priority will be invoked first. The valid range of
priorities lies between EV::MAXPRI (default 2) and EV::MINPRI (default
-2). If the priority is outside this range it will automatically be
normalised to the nearest valid priority.
The default priority of any newly-created watcher is 0.
Note that the priority semantics have not yet been fleshed out and are
subject to almost certain change.
- $w->invoke ($revents)
- Call the callback *now* with the given event mask.
- $w->feed_event ($revents)
- Feed some events on this watcher into EV. EV will react to this call as if
the watcher had received the given $revents mask.
- $revents = $w->clear_pending
- If the watcher is pending, this function clears its pending status and
returns its $revents bitset (as if its callback was invoked). If the
watcher isn't pending it does nothing and returns 0.
- $previous_state = $w->keepalive ($bool)
- Normally, "EV::loop" will return when there are no active
watchers (which is a "deadlock" because no progress can be made
anymore). This is convenient because it allows you to start your watchers
(and your jobs), call "EV::loop" once and when it returns you
know that all your jobs are finished (or they forgot to register some
watchers for their task :).
Sometimes, however, this gets in your way, for example when the module that
calls "EV::loop" (usually the main program) is not the same
module as a long-living watcher (for example a DNS client module written
by somebody else even). Then you might want any outstanding requests to be
handled, but you would not want to keep "EV::loop" from
returning just because you happen to have this long-running UDP port
watcher.
In this case you can clear the keepalive status, which means that even
though your watcher is active, it won't keep "EV::loop" from
returning.
The initial value for keepalive is true (enabled), and you can change it any
time.
Example: Register an I/O watcher for some UDP socket but do not keep the
event loop from running just because of that watcher.
my $udp_socket = ...
my $udp_watcher = EV::io $udp_socket, EV::READ, sub { ... };
$udp_watcher->keepalive (0);
- $loop = $w->loop
- Return the loop that this watcher is attached to.
WATCHER TYPES¶
Each of the following subsections describes a single watcher type.
I/O WATCHERS - is this file descriptor readable or writable?
- $w = EV::io $fileno_or_fh, $eventmask, $callback
- $w = EV::io_ns $fileno_or_fh, $eventmask, $callback
- $w = $loop->io ($fileno_or_fh, $eventmask, $callback)
- $w = $loop->io_ns ($fileno_or_fh, $eventmask, $callback)
- As long as the returned watcher object is alive, call the $callback when
at least one of events specified in $eventmask occurs.
The $eventmask can be one or more of these constants ORed together:
EV::READ wait until read() wouldn't block anymore
EV::WRITE wait until write() wouldn't block anymore
The "io_ns" variant doesn't start (activate) the newly created
watcher.
- $w->set ($fileno_or_fh, $eventmask)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $current_fh = $w->fh
- $old_fh = $w->fh ($new_fh)
- Returns the previously set filehandle and optionally set a new one.
- $current_eventmask = $w->events
- $old_eventmask = $w->events ($new_eventmask)
- Returns the previously set event mask and optionally set a new one.
TIMER WATCHERS - relative and optionally repeating timeouts
- $w = EV::timer $after, $repeat, $callback
- $w = EV::timer_ns $after, $repeat, $callback
- $w = $loop->timer ($after, $repeat, $callback)
- $w = $loop->timer_ns ($after, $repeat, $callback)
- Calls the callback after $after seconds (which may be fractional). If
$repeat is non-zero, the timer will be restarted (with the $repeat value
as $after) after the callback returns.
This means that the callback would be called roughly after $after seconds,
and then every $repeat seconds. The timer does his best not to drift, but
it will not invoke the timer more often then once per event loop
iteration, and might drift in other cases. If that isn't acceptable, look
at EV::periodic, which can provide long-term stable timers.
The timer is based on a monotonic clock, that is, if somebody is sitting in
front of the machine while the timer is running and changes the system
clock, the timer will nevertheless run (roughly) the same time.
The "timer_ns" variant doesn't start (activate) the newly created
watcher.
- $w->set ($after, $repeat)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $w->again
- Similar to the "start" method, but has special semantics for
repeating timers:
If the timer is active and non-repeating, it will be stopped.
If the timer is active and repeating, reset the timeout to occur $repeat
seconds after now.
If the timer is inactive and repeating, start it using the repeat value.
Otherwise do nothing.
This behaviour is useful when you have a timeout for some IO operation. You
create a timer object with the same value for $after and $repeat, and
then, in the read/write watcher, run the "again" method on the
timeout.
PERIODIC WATCHERS - to cron or not to cron?
- $w = EV::periodic $at, $interval, $reschedule_cb, $callback
- $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
- $w = $loop->periodic ($at, $interval, $reschedule_cb, $callback)
- $w = $loop->periodic_ns ($at, $interval, $reschedule_cb,
$callback)
- Similar to EV::timer, but is not based on relative timeouts but on
absolute times. Apart from creating "simple" timers that trigger
"at" the specified time, it can also be used for non-drifting
absolute timers and more complex, cron-like, setups that are not adversely
affected by time jumps (i.e. when the system clock is changed by explicit
date -s or other means such as ntpd). It is also the most complex watcher
type in EV.
It has three distinct "modes":
- •
- absolute timer ($interval = $reschedule_cb = 0)
This time simply fires at the wallclock time $at and doesn't repeat. It will
not adjust when a time jump occurs, that is, if it is to be run at January
1st 2011 then it will run when the system time reaches or surpasses this
time.
- •
- repeating interval timer ($interval > 0, $reschedule_cb = 0)
In this mode the watcher will always be scheduled to time out at the next
"$at + N * $interval" time (for some integer N) and then repeat,
regardless of any time jumps.
This can be used to create timers that do not drift with respect to system
time:
my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
That doesn't mean there will always be 3600 seconds in between triggers, but
only that the the callback will be called when the system time shows a
full hour (UTC).
Another way to think about it (for the mathematically inclined) is that
EV::periodic will try to run the callback in this mode at the next
possible time where "$time = $at (mod $interval)", regardless of
any time jumps.
- •
- manual reschedule mode ($reschedule_cb = coderef)
In this mode $interval and $at are both being ignored. Instead, each time
the periodic watcher gets scheduled, the reschedule callback
($reschedule_cb) will be called with the watcher as first, and the current
time as second argument.
This callback MUST NOT stop or destroy this or any other periodic
watcher, ever, and MUST NOT call any event loop functions or
methods. If you need to stop it, return 1e30 and stop it afterwards.
You may create and start a "EV::prepare" watcher for this task.
It must return the next time to trigger, based on the passed time value
(that is, the lowest time value larger than or equal to to the second
argument). It will usually be called just before the callback will be
triggered, but might be called at other times, too.
This can be used to create very complex timers, such as a timer that
triggers on each midnight, local time (actually 24 hours after the last
midnight, to keep the example simple. If you know a way to do it correctly
in about the same space (without requiring elaborate modules), drop me a
note :):
my $daily = EV::periodic 0, 0, sub {
my ($w, $now) = @_;
use Time::Local ();
my (undef, undef, undef, $d, $m, $y) = localtime $now;
86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
}, sub {
print "it's midnight or likely shortly after, now\n";
};
The "periodic_ns" variant doesn't start (activate) the newly created
watcher.
- $w->set ($at, $interval, $reschedule_cb)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $w->again
- Simply stops and starts the watcher again.
- $time = $w->at
- Return the time that the watcher is expected to trigger next.
SIGNAL WATCHERS - signal me when a signal gets signalled!
- $w = EV::signal $signal, $callback
- $w = EV::signal_ns $signal, $callback
- $w = $loop->signal ($signal, $callback)
- $w = $loop->signal_ns ($signal, $callback)
- Call the callback when $signal is received (the signal can be specified by
number or by name, just as with "kill" or %SIG).
Only one event loop can grab a given signal - attempting to grab the same
signal from two EV loops will crash the program immediately or cause data
corruption.
EV will grab the signal for the process (the kernel only allows one
component to receive a signal at a time) when you start a signal watcher,
and removes it again when you stop it. Perl does the same when you
add/remove callbacks to %SIG, so watch out.
You can have as many signal watchers per signal as you want.
The "signal_ns" variant doesn't start (activate) the newly created
watcher.
- $w->set ($signal)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $current_signum = $w->signal
- $old_signum = $w->signal ($new_signal)
- Returns the previously set signal (always as a number not name) and
optionally set a new one.
CHILD WATCHERS - watch out for process status changes
- $w = EV::child $pid, $trace, $callback
- $w = EV::child_ns $pid, $trace, $callback
- $w = $loop->child ($pid, $trace, $callback)
- $w = $loop->child_ns ($pid, $trace, $callback)
- Call the callback when a status change for pid $pid (or any pid if $pid is
0) has been received (a status change happens when the process terminates
or is killed, or, when trace is true, additionally when it is stopped or
continued). More precisely: when the process receives a
"SIGCHLD", EV will fetch the outstanding exit/wait status for
all changed/zombie children and call the callback.
It is valid (and fully supported) to install a child watcher after a child
has exited but before the event loop has started its next iteration (for
example, first you "fork", then the new child process might
exit, and only then do you install a child watcher in the parent for the
new pid).
You can access both exit (or tracing) status and pid by using the
"rstatus" and "rpid" methods on the watcher object.
You can have as many pid watchers per pid as you want, they will all be
called.
The "child_ns" variant doesn't start (activate) the newly created
watcher.
- $w->set ($pid, $trace)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $current_pid = $w->pid
- Returns the previously set process id and optionally set a new one.
- $exit_status = $w->rstatus
- Return the exit/wait status (as returned by waitpid, see the waitpid entry
in perlfunc).
- $pid = $w->rpid
- Return the pid of the awaited child (useful when you have installed a
watcher for all pids).
STAT WATCHERS - did the file attributes just change?
- $w = EV::stat $path, $interval, $callback
- $w = EV::stat_ns $path, $interval, $callback
- $w = $loop->stat ($path, $interval, $callback)
- $w = $loop->stat_ns ($path, $interval, $callback)
- Call the callback when a file status change has been detected on $path.
The $path does not need to exist, changing from "path exists" to
"path does not exist" is a status change like any other.
The $interval is a recommended polling interval for systems where
OS-supported change notifications don't exist or are not supported. If you
use 0 then an unspecified default is used (which is highly recommended!),
which is to be expected to be around five seconds usually.
This watcher type is not meant for massive numbers of stat watchers, as even
with OS-supported change notifications, this can be resource-intensive.
The "stat_ns" variant doesn't start (activate) the newly created
watcher.
- ... = $w->stat
- This call is very similar to the perl "stat" built-in: It stats
(using "lstat") the path specified in the watcher and sets perls
stat cache (as well as EV's idea of the current stat values) to the values
found.
In scalar context, a boolean is return indicating success or failure of the
stat. In list context, the same 13-value list as with stat is returned
(except that the blksize and blocks fields are not reliable).
In the case of an error, errno is set to "ENOENT" (regardless of
the actual error value) and the "nlink" value is forced to zero
(if the stat was successful then nlink is guaranteed to be non-zero).
See also the next two entries for more info.
- ... = $w->attr
- Just like "$w->stat", but without the initial stat'ing: this
returns the values most recently detected by EV. See the next entry for
more info.
- ... = $w->prev
- Just like "$w->stat", but without the initial stat'ing: this
returns the previous set of values, before the change.
That is, when the watcher callback is invoked, "$w->prev" will
be set to the values found before a change was detected, while
"$w->attr" returns the values found leading to the change
detection. The difference (if any) between "prev" and
"attr" is what triggered the callback.
If you did something to the filesystem object and do not want to trigger yet
another change, you can call "stat" to update EV's idea of what
the current attributes are.
- $w->set ($path, $interval)
- Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
- $current_path = $w->path
- $old_path = $w->path ($new_path)
- Returns the previously set path and optionally set a new one.
- $current_interval = $w->interval
- $old_interval = $w->interval ($new_interval)
- Returns the previously set interval and optionally set a new one. Can be
used to query the actual interval used.
IDLE WATCHERS - when you've got nothing better to do...
- $w = EV::idle $callback
- $w = EV::idle_ns $callback
- $w = $loop->idle ($callback)
- $w = $loop->idle_ns ($callback)
- Call the callback when there are no other pending watchers of the same or
higher priority (excluding check, prepare and other idle watchers of the
same or lower priority, of course). They are called idle watchers because
when the watcher is the highest priority pending event in the process, the
process is considered to be idle at that priority.
If you want a watcher that is only ever called when no other events
are outstanding you have to set the priority to "EV::MINPRI".
The process will not block as long as any idle watchers are active, and they
will be called repeatedly until stopped.
For example, if you have idle watchers at priority 0 and 1, and an I/O
watcher at priority 0, then the idle watcher at priority 1 and the I/O
watcher will always run when ready. Only when the idle watcher at priority
1 is stopped and the I/O watcher at priority 0 is not pending with the
0-priority idle watcher be invoked.
The "idle_ns" variant doesn't start (activate) the newly created
watcher.
PREPARE WATCHERS - customise your event loop!
- $w = EV::prepare $callback
- $w = EV::prepare_ns $callback
- $w = $loop->prepare ($callback)
- $w = $loop->prepare_ns ($callback)
- Call the callback just before the process would block. You can still
create/modify any watchers at this point.
See the EV::check watcher, below, for explanations and an example.
The "prepare_ns" variant doesn't start (activate) the newly
created watcher.
CHECK WATCHERS - customise your event loop even more!
- $w = EV::check $callback
- $w = EV::check_ns $callback
- $w = $loop->check ($callback)
- $w = $loop->check_ns ($callback)
- Call the callback just after the process wakes up again (after it has
gathered events), but before any other callbacks have been invoked.
This can be used to integrate other event-based software into the EV
mainloop: You register a prepare callback and in there, you create io and
timer watchers as required by the other software. Here is a real-world
example of integrating Net::SNMP (with some details left out):
our @snmp_watcher;
our $snmp_prepare = EV::prepare sub {
# do nothing unless active
$dispatcher->{_event_queue_h}
or return;
# make the dispatcher handle any outstanding stuff
... not shown
# create an I/O watcher for each and every socket
@snmp_watcher = (
(map { EV::io $_, EV::READ, sub { } }
keys %{ $dispatcher->{_descriptors} }),
EV::timer +($event->[Net::SNMP::Dispatcher::_ACTIVE]
? $event->[Net::SNMP::Dispatcher::_TIME] - EV::now : 0),
0, sub { },
);
};
The callbacks are irrelevant (and are not even being called), the only
purpose of those watchers is to wake up the process as soon as one of
those events occurs (socket readable, or timer timed out). The
corresponding EV::check watcher will then clean up:
our $snmp_check = EV::check sub {
# destroy all watchers
@snmp_watcher = ();
# make the dispatcher handle any new stuff
... not shown
};
The callbacks of the created watchers will not be called as the watchers are
destroyed before this can happen (remember EV::check gets called first).
The "check_ns" variant doesn't start (activate) the newly created
watcher.
- EV::CHECK constant issues
- Like all other watcher types, there is a bitmask constant for use in
$revents and other places. The "EV::CHECK" is special as it has
the same name as the "CHECK" sub called by Perl. This doesn't
cause big issues on newer perls (beginning with 5.8.9), but it means
thatthe constant must be inlined, i.e. runtime calls will not work.
That means that as long as you always "use EV" and then
"EV::CHECK" you are on the safe side.
FORK WATCHERS - the audacity to resume the event loop after a fork
Fork watchers are called when a "fork ()" was detected. The invocation
is done before the event loop blocks next and before "check"
watchers are being called, and only in the child after the fork.
- $w = EV::fork $callback
- $w = EV::fork_ns $callback
- $w = $loop->fork ($callback)
- $w = $loop->fork_ns ($callback)
- Call the callback before the event loop is resumed in the child process
after a fork.
The "fork_ns" variant doesn't start (activate) the newly created
watcher.
EMBED WATCHERS - when one backend isn't enough...
This is a rather advanced watcher type that lets you embed one event loop into
another (currently only IO events are supported in the embedded loop, other
types of watchers might be handled in a delayed or incorrect fashion and must
not be used).
See the libev documentation at
<
http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#code_ev_embed_code_when_one_backend_>
(locally installed as
EV::libev) for more details.
In short, this watcher is most useful on BSD systems without working kqueue to
still be able to handle a large number of sockets:
my $socket_loop;
# check wether we use SELECT or POLL _and_ KQUEUE is supported
if (
(EV::backend & (EV::BACKEND_POLL | EV::BACKEND_SELECT))
&& (EV::supported_backends & EV::embeddable_backends & EV::BACKEND_KQUEUE)
) {
# use kqueue for sockets
$socket_loop = new EV::Loop EV::BACKEND_KQUEUE | EV::FLAG_NOENV;
}
# use the default loop otherwise
$socket_loop ||= EV::default_loop;
- $w = EV::embed $otherloop[, $callback]
- $w = EV::embed_ns $otherloop[, $callback]
- $w = $loop->embed ($otherloop[, $callback])
- $w = $loop->embed_ns ($otherloop[, $callback])
- Call the callback when the embedded event loop ($otherloop) has any I/O
activity. The $callback is optional: if it is missing, then the embedded
event loop will be managed automatically (which is recommended), otherwise
you have to invoke "sweep" yourself.
The "embed_ns" variant doesn't start (activate) the newly created
watcher.
ASYNC WATCHERS - how to wake up another event loop
Async watchers are provided by EV, but have little use in perl directly, as perl
neither supports threads running in parallel nor direct access to signal
handlers or other contexts where they could be of value.
It is, however, possible to use them from the XS level.
Please see the libev documentation for further details.
- $w = EV::async $callback
- $w = EV::async_ns $callback
- $w = $loop->async ($callback)
- $w = $loop->async_ns ($callback)
- $w->send
- $bool = $w->async_pending
CLEANUP WATCHERS - how to clean up when the event loop goes away
Cleanup watchers are not supported on the Perl level, they can only be used via
XS currently.
PERL SIGNALS¶
While Perl signal handling (%SIG) is not affected by EV, the behaviour with EV
is as the same as any other C library: Perl-signals will only be handled when
Perl runs, which means your signal handler might be invoked only the next time
an event callback is invoked.
The solution is to use EV signal watchers (see "EV::signal"), which
will ensure proper operations with regards to other event watchers.
If you cannot do this for whatever reason, you can also force a watcher to be
called on every event loop iteration by installing a "EV::check"
watcher:
my $async_check = EV::check sub { };
This ensures that perl gets into control for a short time to handle any pending
signals, and also ensures (slightly) slower overall operation.
ITHREADS¶
Ithreads are not supported by this module in any way. Perl pseudo-threads is
evil stuff and must die. Real threads as provided by Coro are fully supported
(and enhanced support is available via Coro::EV).
FORK¶
Most of the "improved" event delivering mechanisms of modern operating
systems have quite a few problems with
fork(2) (to put it bluntly: it
is not supported and usually destructive). Libev makes it possible to work
around this by having a function that recreates the kernel state after fork in
the child.
On non-win32 platforms, this module requires the pthread_atfork functionality to
do this automatically for you. This function is quite buggy on most BSDs,
though, so YMMV. The overhead for this is quite negligible, because everything
the function currently does is set a flag that is checked only when the event
loop gets used the next time, so when you do fork but not use EV, the overhead
is minimal.
On win32, there is no notion of fork so all this doesn't apply, of course.
SEE ALSO¶
EV::MakeMaker - MakeMaker interface to XS API, EV::ADNS (asynchronous DNS),
Glib::EV (makes Glib/Gtk2 use EV as event loop), EV::Glib (embed Glib into
EV), Coro::EV (efficient thread integration), Net::SNMP::EV (asynchronous
SNMP), AnyEvent for event-loop agnostic and portable event driven programming.
AUTHOR¶
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/