EV
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=head1 NAME
EV - perl interface to libev, a high performance full-featured event loop
=head1 SYNOPSIS
use EV;
# TIMERS
my $w = EV::timer 2, 0, sub {
warn "is called after 2s";
};
my $w = EV::timer 0, 3, sub {
warn "is called as soon as possible, then every 3s";
};
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 $pid, 0, sub {
my ($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
=head1 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 L<AnyEvent> instead,
specifically the simplified API described in L<AE>.
When used with EV as backend, the L<AE> API is as fast as the native L<EV>
API, but your programs/modules will still run with many other event loops.
=head1 DESCRIPTION
This module provides an interface to libev
(L<http://software.schmorp.de/pkg/libev.html>). While the documentation
below is comprehensive, one might also consult the documentation of
libev itself (L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod> or
F<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 C<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 L<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.
=head2 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).
=item $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.
=item EV::now_update
=item $loop->now_update
Establishes the current time by querying the kernel, updating the time
returned by C<EV::now> in the progress. This is a costly operation and
is usually done automatically within C<EV::run>.
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.
=item EV::suspend
=item $loop->suspend
=item EV::resume
=item $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 C<^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 C<suspend>
in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
C<resume> directly afterwards to resume timer processing.
Effectively, all C<timer> watchers will be delayed by the time spend
between C<suspend> and C<resume>, and all C<periodic> watchers
will be rescheduled (that is, they will lose any events that would have
occured while suspended).
After calling C<suspend> you B<must not> call I<any> function on the given
loop other than C<resume>, and you B<must not> call C<resume>
without a previous call to C<suspend>.
Calling C<suspend>/C<resume> has the side effect of updating the event
loop time (see C<now_update>).
=item $backend = EV::backend
=item $backend = $loop->backend
Returns an integer describing the backend used by libev (EV::BACKEND_SELECT
or EV::BACKEND_EPOLL).
=item $active = EV::run [$flags]
=item $active = $loop->run ([$flags])
Begin checking for events and calling callbacks. It returns when a
callback calls EV::break or the flags 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 return value can generally be interpreted as "if true, there is
more work left to do".
The $flags argument can be one of the following:
0 as above
EV::RUN_ONCE block at most once (wait, but do not loop)
EV::RUN_NOWAIT do not block at all (fetch/handle events but do not wait)
=item EV::break [$how]
=item $loop->break ([$how])
When called with no arguments or an argument of EV::BREAK_ONE, makes the
innermost call to EV::run return.
When called with an argument of EV::BREAK_ALL, all calls to EV::run will
return as fast as possible.
When called with an argument of EV::BREAK_CANCEL, any pending break will
be cancelled.
=item $count = EV::iteration
=item $count = $loop->iteration
Return the number of times the event loop has polled for new
events. Sometimes useful as a generation counter.
=item EV::once $fh_or_undef, $events, $timeout, $cb->($revents)
=item $loop->once ($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 C<$fh_or_undef> is a filehandle or file descriptor, then C<$events>
must be a bitset containing either C<EV::READ>, C<EV::WRITE> or C<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 C<undef> for
C<$fh_or_undef> and C<0> for C<$events>).
If timeout is C<undef> or negative, then there will be no
timeout. Otherwise an C<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 C<EV::ERROR>, C<EV::READ>,
C<EV::WRITE> and C<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.
=item EV::feed_fd_event $fd, $revents
=item $loop->feed_fd_event ($fd, $revents)
Feed an event on a file descriptor into EV. EV will react to this call as
if the readyness notifications specified by C<$revents> (a combination of
C<EV::READ> and C<EV::WRITE>) happened on the file descriptor C<$fd>.
=item EV::feed_signal_event $signal
Feed a signal event into the default loop. EV will react to this call as
if the signal specified by C<$signal> had occured.
=item EV::feed_signal $signal
Feed a signal event into EV - unlike C<EV::feed_signal_event>, this works
regardless of which loop has registered the signal, and is mainly useful
for custom signal implementations.
=item EV::set_io_collect_interval $time
=item $loop->set_io_collect_interval ($time)
=item EV::set_timeout_collect_interval $time
=item $loop->set_timeout_collect_interval ($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
L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#FUNCTIONS_CONTROLLING_THE_EVENT_LOOP>
(locally installed as F<EV::libev>) for a more detailed discussion.
=item $count = EV::pending_count
=item $count = $loop->pending_count
Returns the number of currently pending watchers.
=item EV::invoke_pending
=item $loop->invoke_pending
Invoke all currently pending watchers.
=back
=head1 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 C<_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 I<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.
=head2 COMMON WATCHER METHODS
This section lists methods common to all watchers.
=over 4
=item $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 C<_ns> variants if you need stopped watchers).
=item $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.
=item $bool = $w->is_active
Returns true if the watcher is active, false otherwise.
=item $current_data = $w->data
=item $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!");
=item $current_cb = $w->cb
=item $old_cb = $w->cb ($new_cb)
Queries the callback on the watcher and optionally changes it. You can do
The C<periodic_ns> variant doesn't start (activate) the newly created watcher.
=item $w->set ($at, $interval, $reschedule_cb)
Reconfigures the watcher, see the constructor above for details. Can be called at
any time.
=item $w->again
Simply stops and starts the watcher again.
=item $time = $w->at
Return the time that the watcher is expected to trigger next.
=item $offset = $w->offset
=item $old_offset = $w->offset ($new_offset)
Returns the current value of the offset attribute and optionally sets a
new one. Setting the new one will not restart the watcher - if the watcher
is active, the new offset value is used whenever it expires next.
=item $interval = $w->interval
=item $old_interval = $w->interval ($new_interval)
See above, for the interval attribute.
=item $reschedule_cb = $w->reschedule_cb
=item $old_reschedule_cb = $w->reschedule_cb ($new_reschedule_cb)
See above, for the reschedule callback.
=back
=head3 SIGNAL WATCHERS - signal me when a signal gets signalled!
=over 4
=item $w = EV::signal $signal, $callback
=item $w = EV::signal_ns $signal, $callback
=item $w = $loop->signal ($signal, $callback)
=item $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 C<kill> or C<%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 C<%SIG>, so watch out.
You can have as many signal watchers per signal as you want.
The C<signal_ns> variant doesn't start (activate) the newly created watcher.
=item $w->set ($signal)
Reconfigures the watcher, see the constructor above for details. Can be
called at any time.
=item $current_signum = $w->signal
=item $old_signum = $w->signal ($new_signal)
Returns the previously set signal (always as a number not name) and
optionally set a new one.
=back
=head3 CHILD WATCHERS - watch out for process status changes
=over 4
=item $w = EV::child $pid, $trace, $callback
=item $w = EV::child_ns $pid, $trace, $callback
=item $w = $loop->child ($pid, $trace, $callback)
=item $w = $loop->child_ns ($pid, $trace, $callback)
Call the callback when a status change for pid C<$pid> (or any pid
if C<$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 C<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 C<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
C<rstatus> and C<rpid> methods on the watcher object.
You can have as many pid watchers per pid as you want, they will all be
called.
The C<child_ns> variant doesn't start (activate) the newly created watcher.
=item $w->set ($pid, $trace)
Reconfigures the watcher, see the constructor above for details. Can be called at
any time.
=item $current_pid = $w->pid
Returns the previously set process id and optionally set a new one.
=item $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 I<no> other events are
outstanding you have to set the priority to C<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 C<0> and C<1>, and
an I/O watcher at priority C<0>, then the idle watcher at priority C<1>
and the I/O watcher will always run when ready. Only when the idle watcher
at priority C<1> is stopped and the I/O watcher at priority C<0> is not
pending with the C<0>-priority idle watcher be invoked.
The C<idle_ns> variant doesn't start (activate) the newly created watcher.
=back
=head3 PREPARE WATCHERS - customise your event loop!
=over 4
=item $w = EV::prepare $callback
=item $w = EV::prepare_ns $callback
=item $w = $loop->prepare ($callback)
=item $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 C<prepare_ns> variant doesn't start (activate) the newly created watcher.
=back
=head3 CHECK WATCHERS - customise your event loop even more!
=over 4
=item $w = EV::check $callback
=item $w = EV::check_ns $callback
=item $w = $loop->check ($callback)
=item $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 $snmp_check = EV::check sub {
# destroy all watchers
@snmp_watcher = ();
# make the dispatcher handle any new stuff
... not shown
};
The callbacks of the created watchers will not be called as the watchers
are destroyed before this can happen (remember EV::check gets called
first).
The C<check_ns> variant doesn't start (activate) the newly created watcher.
=item EV::CHECK constant issues
Like all other watcher types, there is a bitmask constant for use in
C<$revents> and other places. The C<EV::CHECK> is special as it has
the same name as the C<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 I<inlined>, i.e. runtime calls will not work. That means
that as long as you always C<use EV> and then C<EV::CHECK> you are on the
safe side.
=back
=head3 FORK WATCHERS - the audacity to resume the event loop after a fork
Fork watchers are called when a C<fork ()> was detected. The invocation
is done before the event loop blocks next and before C<check> watchers
are being called, and only in the child after the fork.
=over 4
=item $w = EV::fork $callback
=item $w = EV::fork_ns $callback
=item $w = $loop->fork ($callback)
=item $w = $loop->fork_ns ($callback)
Call the callback before the event loop is resumed in the child process
after a fork.
The C<fork_ns> variant doesn't start (activate) the newly created watcher.
=back
=head3 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
L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#code_ev_embed_code_when_one_backend_>
(locally installed as F<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 (
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