[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.122 by root, Thu Jan 31 13:10:56 2008 UTC vs.
Revision 1.133 by root, Sun Feb 24 06:50:16 2008 UTC

 =item ev_loop_fork (loop)
 Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
 after fork, and how you do this is entirely your own problem.
+=item int ev_is_default_loop (loop)
+Returns true when the given loop actually is the default loop, false otherwise.
 =item unsigned int ev_loop_count (loop)
 Returns the count of loop iterations for the loop, which is identical to
 the number of times libev did poll for new events. It starts at C<0> and
 configure a timer to trigger every 10 seconds, then it will trigger at
 exactly 10 second intervals. If, however, your program cannot keep up with
 the timer (because it takes longer than those 10 seconds to do stuff) the
 timer will not fire more than once per event loop iteration.
-=item ev_timer_again (loop)
+=item ev_timer_again (loop, ev_timer *)
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 If the timer is pending, its pending status is cleared.
 In this configuration the watcher triggers an event at the wallclock time
 C<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.
-=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
+=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
 In this mode the watcher will always be scheduled to time out at the next
 C<at + N * interval> time (for some integer N, which can also be negative)
 and then repeat, regardless of any time jumps.
 =item int signum [read-only]
 The signal the watcher watches out for.
 =back
+=head3 Examples
+Example: Try to exit cleanly on SIGINT and SIGTERM.
+  static void
+  sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+  {
+    ev_unloop (loop, EVUNLOOP_ALL);
+  }
+  struct ev_signal signal_watcher;
+  ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
+  ev_signal_start (loop, &sigint_cb);
 =head2 C<ev_child> - watch out for process status changes
 Child watchers trigger when your process receives a SIGCHLD in response to
 The process exit/trace status caused by C<rpid> (see your systems
 C<waitpid> and C<sys/wait.h> documentation for details).
 =back
-=head3 Examples
-Example: Try to exit cleanly on SIGINT and SIGTERM.
-  static void
-  sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
-  {
-    ev_unloop (loop, EVUNLOOP_ALL);
-  }
-  struct ev_signal signal_watcher;
-  ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
-  ev_signal_start (loop, &sigint_cb);
 =head2 C<ev_stat> - did the file attributes just change?
 This watches a filesystem path for attribute changes. That is, it calls
 C<stat> regularly (or when the OS says it changed) and sees if it changed
 The callback will be receive C<EV_STAT> when a change was detected,
 relative to the attributes at the time the watcher was started (or the
 last change was detected).
-=item ev_stat_stat (ev_stat *)
+=item ev_stat_stat (loop, ev_stat *)
 Updates the stat buffer immediately with new values. If you change the
 watched path in your callback, you could call this fucntion to avoid
 detecting this change (while introducing a race condition). Can also be
 useful simply to find out the new values.
 C<ev_async_sent> calls).
 Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
 just the default loop.
+=head3 Queueing
+C<ev_async> does not support queueing of data in any way. The reason
+is that the author does not know of a simple (or any) algorithm for a
+multiple-writer-single-reader queue that works in all cases and doesn't
+need elaborate support such as pthreads.
+That means that if you want to queue data, you have to provide your own
+queue. But at least I can tell you would implement locking around your
+queue:
+=over 4
+=item queueing from a signal handler context
+To implement race-free queueing, you simply add to the queue in the signal
+handler but you block the signal handler in the watcher callback. Here is an example that does that for
+some fictitiuous SIGUSR1 handler:
+   static ev_async mysig;
+   static void
+   sigusr1_handler (void)
+   {
+     sometype data;
+     // no locking etc.
+     queue_put (data);
+     ev_async_send (EV_DEFAULT_ &mysig);
+   }
+   static void
+   mysig_cb (EV_P_ ev_async *w, int revents)
+   {
+     sometype data;
+     sigset_t block, prev;
+     sigemptyset (&block);
+     sigaddset (&block, SIGUSR1);
+     sigprocmask (SIG_BLOCK, &block, &prev);
+     while (queue_get (&data))
+       process (data);
+     if (sigismember (&prev, SIGUSR1)
+       sigprocmask (SIG_UNBLOCK, &block, 0);
+   }
+(Note: pthreads in theory requires you to use C<pthread_setmask>
+instead of C<sigprocmask> when you use threads, but libev doesn't do it
+either...).
+=item queueing from a thread context
+The strategy for threads is different, as you cannot (easily) block
+threads but you can easily preempt them, so to queue safely you need to
+employ a traditional mutex lock, such as in this pthread example:
+   static ev_async mysig;
+   static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
+   static void
+   otherthread (void)
+   {
+     // only need to lock the actual queueing operation
+     pthread_mutex_lock (&mymutex);
+     queue_put (data);
+     pthread_mutex_unlock (&mymutex);
+     ev_async_send (EV_DEFAULT_ &mysig);
+   }
+   static void
+   mysig_cb (EV_P_ ev_async *w, int revents)
+   {
+     pthread_mutex_lock (&mymutex);
+     while (queue_get (&data))
+       process (data);
+     pthread_mutex_unlock (&mymutex);
+   }
+=back
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_async_init (ev_async *, callback)
 If defined to be C<1>, libev will compile in support for the Linux inotify
 interface to speed up C<ev_stat> watchers. Its actual availability will
 be detected at runtime.
+=item EV_ATOMIC_T
+Libev requires an integer type (suitable for storing C<0> or C<1>) whose
+access is atomic with respect to other threads or signal contexts. No such
+type is easily found in the C language, so you can provide your own type
+that you know is safe for your purposes. It is used both for signal handler "locking"
+as well as for signal and thread safety in C<ev_async> watchers.
+In the absense of this define, libev will use C<sig_atomic_t volatile>
+(from F<signal.h>), which is usually good enough on most platforms.
 =item EV_H
 The name of the F<ev.h> header file used to include it. The default if
 undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
 used to virtually rename the F<ev.h> header file in case of conflicts.
 defined to be C<0>, then they are not.
 =item EV_FORK_ENABLE
 If undefined or defined to be C<1>, then fork watchers are supported. If
+defined to be C<0>, then they are not.
+=item EV_ASYNC_ENABLE
+If undefined or defined to be C<1>, then async watchers are supported. If
 defined to be C<0>, then they are not.
 =item EV_MINIMAL
 If you need to shave off some kilobytes of code at the expense of some
 =item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
 That means that changing a timer costs less than removing/adding them
 as only the relative motion in the event queue has to be paid for.
-=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
 These just add the watcher into an array or at the head of a list.
-=item Stopping check/prepare/idle watchers: O(1)
+=item Stopping check/prepare/idle/fork/async watchers: O(1)
 =item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
 These watchers are stored in lists then need to be walked to find the
 correct watcher to remove. The lists are usually short (you don't usually
 =item Priority handling: O(number_of_priorities)
 Priorities are implemented by allocating some space for each
 priority. When doing priority-based operations, libev usually has to
 linearly search all the priorities, but starting/stopping and activating
-watchers becomes O(1) w.r.t. prioritiy handling.
+watchers becomes O(1) w.r.t. priority handling.
+=item Sending an ev_async: O(1)
+=item Processing ev_async_send: O(number_of_async_watchers)
+=item Processing signals: O(max_signal_number)
+Sending involves a syscall I<iff> there were no other C<ev_async_send>
+calls in the current loop iteration. Checking for async and signal events
+involves iterating over all running async watchers or all signal numbers.
 =back
 =head1 Win32 platform limitations and workarounds

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Comparing libev/ev.pod (file contents): Revision 1.122 by root, Thu Jan 31 13:10:56 2008 UTC vs. Revision 1.133 by root, Sun Feb 24 06:50:16 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.122 by root, Thu Jan 31 13:10:56 2008 UTC vs.
Revision 1.133 by root, Sun Feb 24 06:50:16 2008 UTC