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

Comparing libev/ev.pod (file contents):
Revision 1.118 by root, Thu Jan 10 06:00:55 2008 UTC vs.
Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC

 Like C<ev_default_destroy>, but destroys an event loop created by an
 earlier call to C<ev_loop_new>.
 =item ev_default_fork ()
+This function sets a flag that causes subsequent C<ev_loop> iterations
-This function reinitialises the kernel state for backends that have
+to reinitialise the kernel state for backends that have one. Despite the
-one. Despite the name, you can call it anytime, but it makes most sense
+name, you can call it anytime, but it makes most sense after forking, in
-after forking, in either the parent or child process (or both, but that
+the child process (or both child and parent, but that again makes little
-again makes little sense).
+sense). You I<must> call it in the child before using any of the libev
+functions, and it will only take effect at the next C<ev_loop> iteration.
-You I<must> call this function in the child process after forking if and
+On the other hand, you only need to call this function in the child
-only if you want to use the event library in both processes. If you just
+process if and only if you want to use the event library in the child. If
-fork+exec, you don't have to call it.
+you just fork+exec, you don't have to call it at all.
 The function itself is quite fast and it's usually not a problem to call
 it just in case after a fork. To make this easy, the function will fit in
 quite nicely into a call to C<pthread_atfork>:
     pthread_atfork (0, 0, ev_default_fork);
-At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
-without calling this function, so if you force one of those backends you
-do not need to care.
 =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
 =item C<EV_FORK>
 The event loop has been resumed in the child process after fork (see
 C<ev_fork>).
+=item C<EV_ASYNC>
+The given async watcher has been asynchronously notified (see C<ev_async>).
 =item C<EV_ERROR>
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 ran out of memory, a file descriptor was found to be closed or any other
 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.
 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
 some child status changes (most typically when a child of yours dies).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
-=item ev_child_init (ev_child *, callback, int pid)
+=item ev_child_init (ev_child *, callback, int pid, int trace)
-=item ev_child_set (ev_child *, int pid)
+=item ev_child_set (ev_child *, int pid, int trace)
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see
 the status word (use the macros from C<sys/wait.h> and see your systems
 C<waitpid> documentation). The C<rpid> member contains the pid of the
-process causing the status change.
+process causing the status change. C<trace> must be either C<0> (only
+activate the watcher when the process terminates) or C<1> (additionally
+activate the watcher when the process is stopped or continued).
 =item int pid [read-only]
 The process id this watcher watches out for, or C<0>, meaning any process id.
 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
 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.
   static void
   idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
   {
     free (w);
     // now do something you wanted to do when the program has
-    // no longer asnything immediate to do.
+    // no longer anything immediate to do.
   }
   struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
   ev_idle_init (idle_watcher, idle_cb);
   ev_idle_start (loop, idle_cb);
 believe me.
 =back
+=head2 C<ev_async> - how to wake up another event loop
+In general, you cannot use an C<ev_loop> from multiple threads or other
+asynchronous sources such as signal handlers (as opposed to multiple event
+loops - those are of course safe to use in different threads).
+Sometimes, however, you need to wake up another event loop you do not
+control, for example because it belongs to another thread. This is what
+C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
+can signal it by calling C<ev_async_send>, which is thread- and signal
+safe.
+This functionality is very similar to C<ev_signal> watchers, as signals,
+too, are asynchronous in nature, and signals, too, will be compressed
+(i.e. the number of callback invocations may be less than the number of
+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 (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 (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)
+Initialises and configures the async watcher - it has no parameters of any
+kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
+believe me.
+=item ev_async_send (loop, ev_async *)
+Sends/signals/activates the given C<ev_async> watcher, that is, feeds
+an C<EV_ASYNC> event on the watcher into the event loop. Unlike
+C<ev_feed_event>, this call is safe to do in other threads, signal or
+similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
+section below on what exactly this means).
+This call incurs the overhead of a syscall only once per loop iteration,
+so while the overhead might be noticable, it doesn't apply to repeated
+calls to C<ev_async_send>.
+=back
 =head1 OTHER FUNCTIONS
 There are some other functions of possible interest. Described. Here. Now.
 =over 4
 Example: Define a class with an IO and idle watcher, start one of them in
 the constructor.
   class myclass
   {
-    ev_io   io;   void io_cb   (ev::io   &w, int revents);
+    ev::io   io;  void io_cb   (ev::io   &w, int revents);
-    ev_idle idle  void idle_cb (ev::idle &w, int revents);
+    ev:idle idle  void idle_cb (ev::idle &w, int revents);
-    myclass ();
+    myclass (int fd)
-  }
-  myclass::myclass (int fd)
-  {
+    {
-    io  .set <myclass, &myclass::io_cb  > (this);
+      io  .set <myclass, &myclass::io_cb  > (this);
-    idle.set <myclass, &myclass::idle_cb> (this);
+      idle.set <myclass, &myclass::idle_cb> (this);
-    io.start (fd, ev::READ);
+      io.start (fd, ev::READ);
+    }
-  }
+  };
 =head1 MACRO MAGIC
 Libev can be compiled with a variety of options, the most fundamantal
 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 1.118 by root, Thu Jan 10 06:00:55 2008 UTC vs. Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.118 by root, Thu Jan 10 06:00:55 2008 UTC vs.
Revision 1.132 by root, Wed Feb 20 17:45:29 2008 UTC