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NAME |
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EV - perl interface to libev, a high performance full-featured event |
3 |
loop |
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|
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SYNOPSIS |
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use EV; |
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|
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# TIMERS |
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|
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my $w = EV::timer 2, 0, sub { |
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warn "is called after 2s"; |
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}; |
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|
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my $w = EV::timer 2, 2, sub { |
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warn "is called roughly every 2s (repeat = 2)"; |
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}; |
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|
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undef $w; # destroy event watcher again |
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|
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my $w = EV::periodic 0, 60, 0, sub { |
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warn "is called every minute, on the minute, exactly"; |
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}; |
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|
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# IO |
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|
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my $w = EV::io *STDIN, EV::READ, sub { |
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my ($w, $revents) = @_; # all callbacks receive the watcher and event mask |
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warn "stdin is readable, you entered: ", <STDIN>; |
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}; |
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|
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# SIGNALS |
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|
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my $w = EV::signal 'QUIT', sub { |
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warn "sigquit received\n"; |
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}; |
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|
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# CHILD/PID STATUS CHANGES |
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|
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my $w = EV::child 666, sub { |
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my ($w, $revents) = @_; |
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my $status = $w->rstatus; |
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}; |
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|
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# STAT CHANGES |
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my $w = EV::stat "/etc/passwd", 10, sub { |
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my ($w, $revents) = @_; |
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warn $w->path, " has changed somehow.\n"; |
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}; |
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|
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# MAINLOOP |
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EV::loop; # loop until EV::unloop is called or all watchers stop |
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EV::loop EV::LOOP_ONESHOT; # block until at least one event could be handled |
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EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block |
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|
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DESCRIPTION |
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This module provides an interface to libev |
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(<http://software.schmorp.de/pkg/libev.html>). While the documentation |
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below is comprehensive, one might also consult the documentation of |
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libev itself (<http://cvs.schmorp.de/libev/ev.html>) for more subtle |
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details on watcher semantics or some discussion on the available |
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backends, or how to force a specific backend with "LIBEV_FLAGS". |
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|
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BASIC INTERFACE |
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$EV::DIED |
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Must contain a reference to a function that is called when a |
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callback throws an exception (with $@ containing thr error). The |
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default prints an informative message and continues. |
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|
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If this callback throws an exception it will be silently ignored. |
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|
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$time = EV::time |
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Returns the current time in (fractional) seconds since the epoch. |
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|
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$time = EV::now |
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Returns the time the last event loop iteration has been started. |
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This is the time that (relative) timers are based on, and refering |
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to it is usually faster then calling EV::time. |
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|
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$method = EV::method |
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Returns an integer describing the backend used by libev |
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(EV::METHOD_SELECT or EV::METHOD_EPOLL). |
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|
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EV::loop [$flags] |
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Begin checking for events and calling callbacks. It returns when a |
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callback calls EV::unloop. |
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|
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The $flags argument can be one of the following: |
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|
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0 as above |
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EV::LOOP_ONESHOT block at most once (wait, but do not loop) |
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EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait) |
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|
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EV::unloop [$how] |
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When called with no arguments or an argument of EV::UNLOOP_ONE, |
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makes the innermost call to EV::loop return. |
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|
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When called with an argument of EV::UNLOOP_ALL, all calls to |
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EV::loop will return as fast as possible. |
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|
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EV::once $fh_or_undef, $events, $timeout, $cb->($revents) |
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This function rolls together an I/O and a timer watcher for a single |
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one-shot event without the need for managing a watcher object. |
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|
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If $fh_or_undef is a filehandle or file descriptor, then $events |
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must be a bitset containing either "EV::READ", "EV::WRITE" or |
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"EV::READ | EV::WRITE", indicating the type of I/O event you want to |
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wait for. If you do not want to wait for some I/O event, specify |
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"undef" for $fh_or_undef and 0 for $events). |
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|
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If timeout is "undef" or negative, then there will be no timeout. |
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Otherwise a EV::timer with this value will be started. |
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|
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When an error occurs or either the timeout or I/O watcher triggers, |
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then the callback will be called with the received event set (in |
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general you can expect it to be a combination of "EV:ERROR", |
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"EV::READ", "EV::WRITE" and "EV::TIMEOUT"). |
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|
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EV::once doesn't return anything: the watchers stay active till |
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either of them triggers, then they will be stopped and freed, and |
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the callback invoked. |
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|
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WATCHER OBJECTS |
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A watcher is an object that gets created to record your interest in some |
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event. For instance, if you want to wait for STDIN to become readable, |
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you would create an EV::io watcher for that: |
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|
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my $watcher = EV::io *STDIN, EV::READ, sub { |
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my ($watcher, $revents) = @_; |
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warn "yeah, STDIN should not be readable without blocking!\n" |
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}; |
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|
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All watchers can be active (waiting for events) or inactive (paused). |
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Only active watchers will have their callbacks invoked. All callbacks |
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will be called with at least two arguments: the watcher and a bitmask of |
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received events. |
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|
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Each watcher type has its associated bit in revents, so you can use the |
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same callback for multiple watchers. The event mask is named after the |
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type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE, |
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EV::periodic sets EV::PERIODIC and so on, with the exception of IO |
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events (which can set both EV::READ and EV::WRITE bits), and EV::timer |
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(which uses EV::TIMEOUT). |
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|
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In the rare case where one wants to create a watcher but not start it at |
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the same time, each constructor has a variant with a trailing "_ns" in |
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its name, e.g. EV::io has a non-starting variant EV::io_ns and so on. |
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|
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Please note that a watcher will automatically be stopped when the |
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watcher object is destroyed, so you *need* to keep the watcher objects |
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returned by the constructors. |
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|
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Also, all methods changing some aspect of a watcher (->set, ->priority, |
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->fh and so on) automatically stop and start it again if it is active, |
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which means pending events get lost. |
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|
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COMMON WATCHER METHODS |
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This section lists methods common to all watchers. |
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|
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$w->start |
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Starts a watcher if it isn't active already. Does nothing to an |
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already active watcher. By default, all watchers start out in the |
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active state (see the description of the "_ns" variants if you need |
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stopped watchers). |
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|
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$w->stop |
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Stop a watcher if it is active. Also clear any pending events |
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(events that have been received but that didn't yet result in a |
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callback invocation), regardless of wether the watcher was active or |
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not. |
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|
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$bool = $w->is_active |
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Returns true if the watcher is active, false otherwise. |
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|
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$current_data = $w->data |
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$old_data = $w->data ($new_data) |
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Queries a freely usable data scalar on the watcher and optionally |
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changes it. This is a way to associate custom data with a watcher: |
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|
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my $w = EV::timer 60, 0, sub { |
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warn $_[0]->data; |
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}; |
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$w->data ("print me!"); |
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|
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$current_cb = $w->cb |
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$old_cb = $w->cb ($new_cb) |
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Queries the callback on the watcher and optionally changes it. You |
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can do this at any time without the watcher restarting. |
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|
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$current_priority = $w->priority |
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$old_priority = $w->priority ($new_priority) |
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Queries the priority on the watcher and optionally changes it. |
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Pending watchers with higher priority will be invoked first. The |
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valid range of priorities lies between EV::MAXPRI (default 2) and |
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EV::MINPRI (default -2). If the priority is outside this range it |
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will automatically be normalised to the nearest valid priority. |
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|
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The default priority of any newly-created watcher is 0. |
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|
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Note that the priority semantics have not yet been fleshed out and |
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are subject to almost certain change. |
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|
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$w->trigger ($revents) |
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Call the callback *now* with the given event mask. |
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|
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$previous_state = $w->keepalive ($bool) |
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Normally, "EV::loop" will return when there are no active watchers |
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(which is a "deadlock" because no progress can be made anymore). |
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This is convinient because it allows you to start your watchers (and |
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your jobs), call "EV::loop" once and when it returns you know that |
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all your jobs are finished (or they forgot to register some watchers |
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for their task :). |
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|
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Sometimes, however, this gets in your way, for example when you the |
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module that calls "EV::loop" (usually the main program) is not the |
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same module as a long-living watcher (for example a DNS client |
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module written by somebody else even). Then you might want any |
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outstanding requests to be handled, but you would not want to keep |
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"EV::loop" from returning just because you happen to have this |
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long-running UDP port watcher. |
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|
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In this case you can clear the keepalive status, which means that |
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even though your watcher is active, it won't keep "EV::loop" from |
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returning. |
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|
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The initial value for keepalive is true (enabled), and you cna |
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change it any time. |
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|
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Example: Register an IO watcher for some UDP socket but do not keep |
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the event loop from running just because of that watcher. |
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|
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my $udp_socket = ... |
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my $udp_watcher = EV::io $udp_socket, EV::READ, sub { ... }; |
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$udp_watcher->keepalive (0); |
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|
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WATCHER TYPES |
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Each of the following subsections describes a single watcher type. |
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|
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IO WATCHERS - is this file descriptor readable or writable? |
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$w = EV::io $fileno_or_fh, $eventmask, $callback |
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$w = EV::io_ns $fileno_or_fh, $eventmask, $callback |
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As long as the returned watcher object is alive, call the $callback |
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when at least one of events specified in $eventmask occurs. |
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|
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The $eventmask can be one or more of these constants ORed together: |
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|
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EV::READ wait until read() wouldn't block anymore |
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EV::WRITE wait until write() wouldn't block anymore |
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|
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The "io_ns" variant doesn't start (activate) the newly created |
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watcher. |
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|
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$w->set ($fileno_or_fh, $eventmask) |
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Reconfigures the watcher, see the constructor above for details. Can |
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be called at any time. |
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|
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$current_fh = $w->fh |
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$old_fh = $w->fh ($new_fh) |
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Returns the previously set filehandle and optionally set a new one. |
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|
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$current_eventmask = $w->events |
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$old_eventmask = $w->events ($new_eventmask) |
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Returns the previously set event mask and optionally set a new one. |
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|
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TIMER WATCHERS - relative and optionally repeating timeouts |
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$w = EV::timer $after, $repeat, $callback |
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$w = EV::timer_ns $after, $repeat, $callback |
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Calls the callback after $after seconds (which may be fractional). |
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If $repeat is non-zero, the timer will be restarted (with the |
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$repeat value as $after) after the callback returns. |
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|
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This means that the callback would be called roughly after $after |
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seconds, and then every $repeat seconds. The timer does his best not |
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to drift, but it will not invoke the timer more often then once per |
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event loop iteration, and might drift in other cases. If that isn't |
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acceptable, look at EV::periodic, which can provide long-term stable |
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timers. |
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|
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The timer is based on a monotonic clock, that is, if somebody is |
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sitting in front of the machine while the timer is running and |
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changes the system clock, the timer will nevertheless run (roughly) |
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the same time. |
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|
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The "timer_ns" variant doesn't start (activate) the newly created |
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watcher. |
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|
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$w->set ($after, $repeat) |
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Reconfigures the watcher, see the constructor above for details. Can |
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be called at any time. |
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|
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$w->again |
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Similar to the "start" method, but has special semantics for |
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repeating timers: |
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|
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If the timer is active and non-repeating, it will be stopped. |
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|
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If the timer is active and repeating, reset the timeout to occur |
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$repeat seconds after now. |
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|
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If the timer is inactive and repeating, start it using the repeat |
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value. |
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|
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Otherwise do nothing. |
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|
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This behaviour is useful when you have a timeout for some IO |
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operation. You create a timer object with the same value for $after |
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and $repeat, and then, in the read/write watcher, run the "again" |
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method on the timeout. |
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|
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PERIODIC WATCHERS - to cron or not to cron? |
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$w = EV::periodic $at, $interval, $reschedule_cb, $callback |
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$w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback |
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Similar to EV::timer, but is not based on relative timeouts but on |
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absolute times. Apart from creating "simple" timers that trigger |
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"at" the specified time, it can also be used for non-drifting |
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absolute timers and more complex, cron-like, setups that are not |
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adversely affected by time jumps (i.e. when the system clock is |
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changed by explicit date -s or other means such as ntpd). It is also |
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the most complex watcher type in EV. |
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|
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It has three distinct "modes": |
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|
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* absolute timer ($interval = $reschedule_cb = 0) |
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This time simply fires at the wallclock time $at and doesn't |
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repeat. It will not adjust when a time jump occurs, that is, if |
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it is to be run at January 1st 2011 then it will run when the |
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system time reaches or surpasses this time. |
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|
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* non-repeating interval timer ($interval > 0, $reschedule_cb = 0) |
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In this mode the watcher will always be scheduled to time out at |
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the next "$at + N * $interval" time (for some integer N) and |
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then repeat, regardless of any time jumps. |
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|
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This can be used to create timers that do not drift with respect |
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to system time: |
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|
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my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" }; |
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|
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That doesn't mean there will always be 3600 seconds in between |
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triggers, but only that the the clalback will be called when the |
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system time shows a full hour (UTC). |
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|
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Another way to think about it (for the mathematically inclined) |
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is that EV::periodic will try to run the callback in this mode |
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at the next possible time where "$time = $at (mod $interval)", |
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regardless of any time jumps. |
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|
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* manual reschedule mode ($reschedule_cb = coderef) |
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In this mode $interval and $at are both being ignored. Instead, |
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each time the periodic watcher gets scheduled, the reschedule |
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callback ($reschedule_cb) will be called with the watcher as |
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first, and the current time as second argument. |
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|
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*This callback MUST NOT stop or destroy this or any other |
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periodic watcher, ever*. If you need to stop it, return 1e30 and |
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stop it afterwards. |
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|
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It must return the next time to trigger, based on the passed |
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time value (that is, the lowest time value larger than to the |
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second argument). It will usually be called just before the |
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callback will be triggered, but might be called at other times, |
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too. |
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|
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This can be used to create very complex timers, such as a timer |
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that triggers on each midnight, local time (actually 24 hours |
365 |
after the last midnight, to keep the example simple. If you know |
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a way to do it correctly in about the same space (without |
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requiring elaborate modules), drop me a note :): |
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|
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my $daily = EV::periodic 0, 0, sub { |
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my ($w, $now) = @_; |
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|
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use Time::Local (); |
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my (undef, undef, undef, $d, $m, $y) = localtime $now; |
374 |
86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y |
375 |
}, sub { |
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print "it's midnight or likely shortly after, now\n"; |
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}; |
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|
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The "periodic_ns" variant doesn't start (activate) the newly created |
380 |
watcher. |
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|
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$w->set ($at, $interval, $reschedule_cb) |
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Reconfigures the watcher, see the constructor above for details. Can |
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be called at any time. |
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|
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$w->again |
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Simply stops and starts the watcher again. |
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|
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SIGNAL WATCHERS - signal me when a signal gets signalled! |
390 |
$w = EV::signal $signal, $callback |
391 |
$w = EV::signal_ns $signal, $callback |
392 |
Call the callback when $signal is received (the signal can be |
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specified by number or by name, just as with "kill" or %SIG). |
394 |
|
395 |
EV will grab the signal for the process (the kernel only allows one |
396 |
component to receive a signal at a time) when you start a signal |
397 |
watcher, and removes it again when you stop it. Perl does the same |
398 |
when you add/remove callbacks to %SIG, so watch out. |
399 |
|
400 |
You can have as many signal watchers per signal as you want. |
401 |
|
402 |
The "signal_ns" variant doesn't start (activate) the newly created |
403 |
watcher. |
404 |
|
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$w->set ($signal) |
406 |
Reconfigures the watcher, see the constructor above for details. Can |
407 |
be called at any time. |
408 |
|
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$current_signum = $w->signal |
410 |
$old_signum = $w->signal ($new_signal) |
411 |
Returns the previously set signal (always as a number not name) and |
412 |
optionally set a new one. |
413 |
|
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CHILD WATCHERS - watch out for process status changes |
415 |
$w = EV::child $pid, $callback |
416 |
$w = EV::child_ns $pid, $callback |
417 |
Call the callback when a status change for pid $pid (or any pid if |
418 |
$pid is 0) has been received. More precisely: when the process |
419 |
receives a "SIGCHLD", EV will fetch the outstanding exit/wait status |
420 |
for all changed/zombie children and call the callback. |
421 |
|
422 |
It is valid (and fully supported) to install a child watcher after a |
423 |
child has exited but before the event loop has started its next |
424 |
iteration (for example, first you "fork", then the new child process |
425 |
might exit, and only then do you install a child watcher in the |
426 |
parent for the new pid). |
427 |
|
428 |
You can access both exit (or tracing) status and pid by using the |
429 |
"rstatus" and "rpid" methods on the watcher object. |
430 |
|
431 |
You can have as many pid watchers per pid as you want, they will all |
432 |
be called. |
433 |
|
434 |
The "child_ns" variant doesn't start (activate) the newly created |
435 |
watcher. |
436 |
|
437 |
$w->set ($pid) |
438 |
Reconfigures the watcher, see the constructor above for details. Can |
439 |
be called at any time. |
440 |
|
441 |
$current_pid = $w->pid |
442 |
$old_pid = $w->pid ($new_pid) |
443 |
Returns the previously set process id and optionally set a new one. |
444 |
|
445 |
$exit_status = $w->rstatus |
446 |
Return the exit/wait status (as returned by waitpid, see the waitpid |
447 |
entry in perlfunc). |
448 |
|
449 |
$pid = $w->rpid |
450 |
Return the pid of the awaited child (useful when you have installed |
451 |
a watcher for all pids). |
452 |
|
453 |
STAT WATCHERS - did the file attributes just change? |
454 |
$w = EV::stat $path, $interval, $callback |
455 |
$w = EV::stat_ns $path, $interval, $callback |
456 |
Call the callback when a file status change has been detected on |
457 |
$path. The $path does not need to exist, changing from "path exists" |
458 |
to "path does not exist" is a status change like any other. |
459 |
|
460 |
The $interval is a recommended polling interval for systems where |
461 |
OS-supported change notifications don't exist or are not supported. |
462 |
If you use 0 then an unspecified default is used (which is highly |
463 |
recommended!), which is to be expected to be around five seconds |
464 |
usually. |
465 |
|
466 |
This watcher type is not meant for massive numbers of stat watchers, |
467 |
as even with OS-supported change notifications, this can be |
468 |
resource-intensive. |
469 |
|
470 |
The "stat_ns" variant doesn't start (activate) the newly created |
471 |
watcher. |
472 |
|
473 |
$w->set ($path, $interval) |
474 |
Reconfigures the watcher, see the constructor above for details. Can |
475 |
be called at any time. |
476 |
|
477 |
$current_path = $w->path |
478 |
$old_path = $w->path ($new_path) |
479 |
Returns the previously set path and optionally set a new one. |
480 |
|
481 |
$current_interval = $w->interval |
482 |
$old_interval = $w->interval ($new_interval) |
483 |
Returns the previously set interval and optionally set a new one. |
484 |
Can be used to query the actual interval used. |
485 |
|
486 |
IDLE WATCHERS - when you've got nothing better to do... |
487 |
$w = EV::idle $callback |
488 |
$w = EV::idle_ns $callback |
489 |
Call the callback when there are no pending io, timer/periodic, |
490 |
signal or child events, i.e. when the process is idle. |
491 |
|
492 |
The process will not block as long as any idle watchers are active, |
493 |
and they will be called repeatedly until stopped. |
494 |
|
495 |
The "idle_ns" variant doesn't start (activate) the newly created |
496 |
watcher. |
497 |
|
498 |
PREPARE WATCHERS - customise your event loop! |
499 |
$w = EV::prepare $callback |
500 |
$w = EV::prepare_ns $callback |
501 |
Call the callback just before the process would block. You can still |
502 |
create/modify any watchers at this point. |
503 |
|
504 |
See the EV::check watcher, below, for explanations and an example. |
505 |
|
506 |
The "prepare_ns" variant doesn't start (activate) the newly created |
507 |
watcher. |
508 |
|
509 |
CHECK WATCHERS - customise your event loop even more! |
510 |
$w = EV::check $callback |
511 |
$w = EV::check_ns $callback |
512 |
Call the callback just after the process wakes up again (after it |
513 |
has gathered events), but before any other callbacks have been |
514 |
invoked. |
515 |
|
516 |
This is used to integrate other event-based software into the EV |
517 |
mainloop: You register a prepare callback and in there, you create |
518 |
io and timer watchers as required by the other software. Here is a |
519 |
real-world example of integrating Net::SNMP (with some details left |
520 |
out): |
521 |
|
522 |
our @snmp_watcher; |
523 |
|
524 |
our $snmp_prepare = EV::prepare sub { |
525 |
# do nothing unless active |
526 |
$dispatcher->{_event_queue_h} |
527 |
or return; |
528 |
|
529 |
# make the dispatcher handle any outstanding stuff |
530 |
... not shown |
531 |
|
532 |
# create an IO watcher for each and every socket |
533 |
@snmp_watcher = ( |
534 |
(map { EV::io $_, EV::READ, sub { } } |
535 |
keys %{ $dispatcher->{_descriptors} }), |
536 |
|
537 |
EV::timer +($event->[Net::SNMP::Dispatcher::_ACTIVE] |
538 |
? $event->[Net::SNMP::Dispatcher::_TIME] - EV::now : 0), |
539 |
0, sub { }, |
540 |
); |
541 |
}; |
542 |
|
543 |
The callbacks are irrelevant (and are not even being called), the |
544 |
only purpose of those watchers is to wake up the process as soon as |
545 |
one of those events occurs (socket readable, or timer timed out). |
546 |
The corresponding EV::check watcher will then clean up: |
547 |
|
548 |
our $snmp_check = EV::check sub { |
549 |
# destroy all watchers |
550 |
@snmp_watcher = (); |
551 |
|
552 |
# make the dispatcher handle any new stuff |
553 |
... not shown |
554 |
}; |
555 |
|
556 |
The callbacks of the created watchers will not be called as the |
557 |
watchers are destroyed before this cna happen (remember EV::check |
558 |
gets called first). |
559 |
|
560 |
The "check_ns" variant doesn't start (activate) the newly created |
561 |
watcher. |
562 |
|
563 |
FORK WATCHERS - the audacity to resume the event loop after a fork |
564 |
Fork watchers are called when a "fork ()" was detected. The invocation |
565 |
is done before the event loop blocks next and before "check" watchers |
566 |
are being called, and only in the child after the fork. |
567 |
|
568 |
$w = EV::fork $callback |
569 |
$w = EV::fork_ns $callback |
570 |
Call the callback before the event loop is resumed in the child |
571 |
process after a fork. |
572 |
|
573 |
The "fork_ns" variant doesn't start (activate) the newly created |
574 |
watcher. |
575 |
|
576 |
THREADS |
577 |
Threads are not supported by this module in any way. Perl pseudo-threads |
578 |
is evil stuff and must die. As soon as Perl gains real threads I will |
579 |
work on thread support for it. |
580 |
|
581 |
FORK |
582 |
Most of the "improved" event delivering mechanisms of modern operating |
583 |
systems have quite a few problems with fork(2) (to put it bluntly: it is |
584 |
not supported and usually destructive). Libev makes it possible to work |
585 |
around this by having a function that recreates the kernel state after |
586 |
fork in the child. |
587 |
|
588 |
On non-win32 platforms, this module requires the pthread_atfork |
589 |
functionality to do this automatically for you. This function is quite |
590 |
buggy on most BSDs, though, so YMMV. The overhead for this is quite |
591 |
negligible, because everything the function currently does is set a flag |
592 |
that is checked only when the event loop gets used the next time, so |
593 |
when you do fork but not use EV, the overhead is minimal. |
594 |
|
595 |
On win32, there is no notion of fork so all this doesn't apply, of |
596 |
course. |
597 |
|
598 |
SEE ALSO |
599 |
EV::DNS. |
600 |
|
601 |
AUTHOR |
602 |
Marc Lehmann <schmorp@schmorp.de> |
603 |
http://home.schmorp.de/ |
604 |
|