Provided by: libev-perl_4.22-1build2_amd64 
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::break 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 occurred 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::break 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 occurred.
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 = 0)
Reconfigures the watcher, see the constructor above for details. Can be called at any
time.
$w->again
$w->again ($repeat)
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.
If called with a $repeat argument, then it uses this a timer repeat value.
$after = $w->remaining
Calculates and returns the remaining time till the timer will fire.
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 whether 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/