[ViewVC] Diff of: cvs/EV/README

Comparing EV/README (file contents):
Revision 1.10 by root, Wed Nov 14 21:25:46 2007 UTC vs.
Revision 1.16 by root, Fri Dec 7 18:11:23 2007 UTC

       # CHILD/PID STATUS CHANGES
       my $w = EV::child 666, sub {
          my ($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::loop;           # loop until EV::unloop is called or all watchers stop
       EV::loop EV::LOOP_ONESHOT;  # block until at least one event could be handled
       EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block
 DESCRIPTION
     This module provides an interface to libev
-    (<http://software.schmorp.de/pkg/libev.html>).
+    (<http://software.schmorp.de/pkg/libev.html>). While the documentation
+    below is comprehensive, one might also consult the documentation of
+    libev itself (<http://cvs.schmorp.de/libev/ev.html>) 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.
 BASIC INTERFACE
     $EV::DIED
         Must contain a reference to a function that is called when a
         callback throws an exception (with $@ containing thr error). The
     $time = EV::now
         Returns the time the last event loop iteration has been started.
         This is the time that (relative) timers are based on, and refering
         to it is usually faster then calling EV::time.
-    $method = EV::ev_method
+    $method = EV::method
         Returns an integer describing the backend used by libev
         (EV::METHOD_SELECT or EV::METHOD_EPOLL).
     EV::loop [$flags]
         Begin checking for events and calling callbacks. It returns when a
         makes the innermost call to EV::loop return.
         When called with an argument of EV::UNLOOP_ALL, all calls to
         EV::loop will return as fast as possible.
-  WATCHER
+    $count = EV::loop_count
+        Return the number of times the event loop has polled for new events.
+        Sometiems useful as a generation counter.
+    EV::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::TIMEOUT").
+        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.
+  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 {
     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 IO
+    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), and EV::timer
     (which uses EV::TIMEOUT).
     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
     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.
-  WATCHER TYPES
+  COMMON WATCHER METHODS
-    Now lets move to the existing watcher types and asociated methods.
+    This section lists methods common to all watchers.
-    The following methods are available for all watchers. Then followes a
-    description of each watcher constructor (EV::io, EV::timer,
-    EV::periodic, EV::signal, EV::child, EV::idle, EV::prepare and
-    EV::check), followed by any type-specific methods (if any).
     $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 wether the watcher was active or
+        callback invocation), regardless of whether the watcher was active
-        not.
+        or not.
     $bool = $w->is_active
         Returns true if the watcher is active, false otherwise.
     $current_data = $w->data
         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 weatcher is 0.
+        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.
     $w->trigger ($revents)
         Call the callback *now* with the given event mask.
+    $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 convinient 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 you 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 cna
+        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);
+  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
         As long as the returned watcher object is alive, call the $callback
-        when the events specified in $eventmask.
+        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
     $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
-        Calls the callback after $after seconds. If $repeat is non-zero, the
+        Calls the callback after $after seconds (which may be fractional).
-        timer will be restarted (with the $repeat value as $after) after the
+        If $repeat is non-zero, the timer will be restarted (with the
-        callback returns.
+        $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
         The "timer_ns" variant doesn't start (activate) the newly created
         watcher.
     $w->set ($after, $repeat)
         Reconfigures the watcher, see the constructor above for details. Can
-        be at any time.
+        be called at any time.
     $w->again
         Similar to the "start" method, but has special semantics for
         repeating timers:
         This behaviour is useful when you have a timeout for some IO
         operation. You create a timer object with the same value for $after
         and $repeat, and then, in the read/write watcher, run the "again"
         method on the timeout.
+   PERIODIC WATCHERS - to cron or not to cron?
     $w = EV::periodic $at, $interval, $reschedule_cb, $callback
     $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
         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
         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 at any time.
+        be called at any time.
     $w->again
         Simply stops and starts the watcher again.
+   SIGNAL WATCHERS - signal me when a signal gets signalled!
     $w = EV::signal $signal, $callback
     $w = EV::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).
+        specified by number or by name, just as with "kill" or %SIG).
         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.
         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 at any time.
+        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, $callback
     $w = EV::child_ns $pid, $callback
         Call the callback when a status change for pid $pid (or any pid if
         $pid is 0) has been received. More precisely: when the process
-        receives a SIGCHLD, EV will fetch the outstanding exit/wait status
+        receives a "SIGCHLD", EV will fetch the outstanding exit/wait status
         for all changed/zombie children and call the callback.
-        You can access both status and pid by using the "rstatus" and "rpid"
+        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
-        methods on the watcher object.
+        "rstatus" and "rpid" methods on the watcher object.
-        You can have as many pid watchers per pid as you want.
+        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)
         Reconfigures the watcher, see the constructor above for details. Can
-        be at any time.
+        be called at any time.
     $current_pid = $w->pid
     $old_pid = $w->pid ($new_pid)
         Returns the previously set process id and optionally set a new one.
     $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
+        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
-        Call the callback when there are no pending io, timer/periodic,
+        Call the callback when there are no other pending watchers of the
-        signal or child events, i.e. when the process is idle.
+        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
         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
         Call the callback just after the process wakes up again (after it
         has gathered events), but before any other callbacks have been
         invoked.
               # do nothing unless active
               $dispatcher->{_event_queue_h}
                  or return;
               # make the dispatcher handle any outstanding stuff
+              ... not shown
-              # create an IO watcher for each and every socket
+              # 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 { },
               );
-              # if there are any timeouts, also create a timer
-              push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
-                 if $event->[Net::SNMP::Dispatcher::_ACTIVE];
            };
-        The callbacks are irrelevant, the only purpose of those watchers is
+        The callbacks are irrelevant (and are not even being called), the
-        to wake up the process as soon as one of those events occurs (socket
+        only purpose of those watchers is to wake up the process as soon as
-        readable, or timer timed out). The corresponding EV::check watcher
+        one of those events occurs (socket readable, or timer timed out).
-        will then clean up:
+        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 cna happen (remember EV::check
         gets called first).
         The "check_ns" variant doesn't start (activate) the newly created
         watcher.
+   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
+        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.
+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 shortly gets into control for a short time, and
+    also ensures slower overall operation.
 THREADS
-    Threads are not supported by this in any way. Perl pseudo-threads is
+    Threads are not supported by this module in any way. Perl pseudo-threads
-    evil stuff and must die.
+    is evil stuff and must die. As soon as Perl gains real threads I will
+    work on thread support for it.
+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
-      L<EV::DNS>, L<EV::AnyEvent>.
+    EV::ADNS (asynchronous dns), Glib::EV (makes Glib/Gtk2 use EV as event
+    loop), Coro::EV (efficient coroutines with EV).
 AUTHOR
      Marc Lehmann <schmorp@schmorp.de>
      http://home.schmorp.de/

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Comparing EV/README (file contents): Revision 1.10 by root, Wed Nov 14 21:25:46 2007 UTC vs. Revision 1.16 by root, Fri Dec 7 18:11:23 2007 UTC

Diff Legend

Comparing EV/README (file contents):
Revision 1.10 by root, Wed Nov 14 21:25:46 2007 UTC vs.
Revision 1.16 by root, Fri Dec 7 18:11:23 2007 UTC