--- libev/ev.pod 2007/12/26 08:06:09 1.112 +++ libev/ev.pod 2008/03/08 07:04:56 1.134 @@ -262,6 +262,13 @@ If you don't know what event loop to use, use the one returned from this function. +The default loop is the only loop that can handle C and +C watchers, and to do this, it always registers a handler +for C. If this is a problem for your app you can either +create a dynamic loop with C that doesn't do that, or you +can simply overwrite the C signal handler I calling +C. + The flags argument can be used to specify special behaviour or specific backends to use, and is usually specified as C<0> (or C). @@ -405,6 +412,10 @@ descriptors a "slow" C or C backend might perform better. +On the positive side, ignoring the spurious readyness notifications, this +backend actually performed to specification in all tests and is fully +embeddable, which is a rare feat among the OS-specific backends. + =item C Try all backends (even potentially broken ones that wouldn't be tried @@ -416,9 +427,8 @@ =back If one or more of these are ored into the flags value, then only these -backends will be tried (in the reverse order as given here). If none are -specified, most compiled-in backend will be tried, usually in reverse -order of their flag values :) +backends will be tried (in the reverse order as listed here). If none are +specified, all backends in C will be tried. The most typical usage is like this: @@ -475,14 +485,16 @@ =item ev_default_fork () -This function reinitialises the kernel state for backends that have -one. Despite the name, you can call it anytime, but it makes most sense -after forking, in either the parent or child process (or both, but that -again makes little sense). - -You I call this function in the child process after forking if and -only if you want to use the event library in both processes. If you just -fork+exec, you don't have to call it. +This function sets a flag that causes subsequent C iterations +to reinitialise the kernel state for backends that have one. Despite the +name, you can call it anytime, but it makes most sense after forking, in +the child process (or both child and parent, but that again makes little +sense). You I call it in the child before using any of the libev +functions, and it will only take effect at the next C iteration. + +On the other hand, you only need to call this function in the child +process if and only if you want to use the event library in the child. If +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 @@ -490,16 +502,16 @@ pthread_atfork (0, 0, ev_default_fork); -At the moment, C and C 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, but acts on an event loop created by C. 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 @@ -553,12 +565,16 @@ Here are the gory details of what C does: - Before the first iteration, call any pending watchers. - * If there are no active watchers (reference count is zero), return. - - Queue all prepare watchers and then call all outstanding watchers. + * If EVFLAG_FORKCHECK was used, check for a fork. + - If a fork was detected, queue and call all fork watchers. + - Queue and call all prepare watchers. - If we have been forked, recreate the kernel state. - Update the kernel state with all outstanding changes. - Update the "event loop time". - - Calculate for how long to block. + - Calculate for how long to sleep or block, if at all + (active idle watchers, EVLOOP_NONBLOCK or not having + any active watchers at all will result in not sleeping). + - Sleep if the I/O and timer collect interval say so. - Block the process, waiting for any events. - Queue all outstanding I/O (fd) events. - Update the "event loop time" and do time jump handling. @@ -569,10 +585,11 @@ - Call all queued watchers in reverse order (i.e. check watchers first). Signals and child watchers are implemented as I/O watchers, and will be handled here by queueing them when their watcher gets executed. - - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK - were used, return, otherwise continue with step *. + - If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK + were used, or there are no active watchers, return, otherwise + continue with step *. -Example: Queue some jobs and then loop until no events are outsanding +Example: Queue some jobs and then loop until no events are outstanding anymore. ... queue jobs here, make sure they register event watchers as long @@ -587,6 +604,8 @@ C, which will make the innermost C call return, or C, which will make all nested C calls return. +This "unloop state" will be cleared when entering C again. + =item ev_ref (loop) =item ev_unref (loop) @@ -600,7 +619,9 @@ visible to the libev user and should not keep C from exiting if no event watchers registered by it are active. It is also an excellent way to do this for generic recurring timers or from within third-party -libraries. Just remember to I and I. +libraries. Just remember to I and I +(but only if the watcher wasn't active before, or was active before, +respectively). Example: Create a signal watcher, but keep it from keeping C running when nothing else is active. @@ -759,6 +780,10 @@ The event loop has been resumed in the child process after fork (see C). +=item C + +The given async watcher has been asynchronously notified (see C). + =item C An unspecified error has occured, the watcher has been stopped. This might @@ -1133,7 +1158,7 @@ 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: @@ -1252,7 +1277,7 @@ 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 time (for some integer N, which can also be negative) @@ -1413,26 +1438,67 @@ =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 - 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). +some child status changes (most typically when a child of yours dies). It +is permissible to install a child watcher I the child has been +forked (which implies it might have already exited), as long as the event +loop isn't entered (or is continued from a watcher). + +Only the default event loop is capable of handling signals, and therefore +you can only rgeister child watchers in the default event loop. + +=head3 Process Interaction + +Libev grabs C as soon as the default event loop is +initialised. This is necessary to guarantee proper behaviour even if +the first child watcher is started after the child exits. The occurance +of C is recorded asynchronously, but child reaping is done +synchronously as part of the event loop processing. Libev always reaps all +children, even ones not watched. + +=head3 Overriding the Built-In Processing + +Libev offers no special support for overriding the built-in child +processing, but if your application collides with libev's default child +handler, you can override it easily by installing your own handler for +C after initialising the default loop, and making sure the +default loop never gets destroyed. You are encouraged, however, to use an +event-based approach to child reaping and thus use libev's support for +that, so other libev users can use C watchers freely. =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 (or I process if C is specified as C<0>). The callback can look at the C member of the C watcher structure to see the status word (use the macros from C and see your systems C documentation). The C member contains the pid of the -process causing the status change. +process causing the status change. C 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] @@ -1451,17 +1517,32 @@ =head3 Examples -Example: Try to exit cleanly on SIGINT and SIGTERM. +Example: C a new process and install a child handler to wait for +its completion. + + ev_child cw; static void - sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) + child_cb (EV_P_ struct ev_child *w, int revents) { - ev_unloop (loop, EVUNLOOP_ALL); + ev_child_stop (EV_A_ w); + printf ("process %d exited with status %x\n", w->rpid, w->rstatus); } - struct ev_signal signal_watcher; - ev_signal_init (&signal_watcher, sigint_cb, SIGINT); - ev_signal_start (loop, &sigint_cb); + pid_t pid = fork (); + + if (pid < 0) + // error + else if (pid == 0) + { + // the forked child executes here + exit (1); + } + else + { + ev_child_init (&cw, child_cb, pid, 0); + ev_child_start (EV_DEFAULT_ &cw); + } =head2 C - did the file attributes just change? @@ -1551,7 +1632,7 @@ 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 @@ -1678,7 +1759,7 @@ { 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)); @@ -2029,6 +2110,137 @@ =back +=head2 C - how to wake up another event loop + +In general, you cannot use an C 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 watchers do: as long as the C watcher is active, you +can signal it by calling C, which is thread- and signal +safe. + +This functionality is very similar to C 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 calls). + +Unlike C watchers, C works with any event loop, not +just the default loop. + +=head3 Queueing + +C 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 +instead of C 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) + +Initialises and configures the async watcher - it has no parameters of any +kind. There is a C macro, but using it is utterly pointless, +believe me. + +=item ev_async_send (loop, ev_async *) + +Sends/signals/activates the given C watcher, that is, feeds +an C event on the watcher into the event loop. Unlike +C, this call is safe to do in other threads, signal or +similar contexts (see the dicusssion of C 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. + +=back + + =head1 OTHER FUNCTIONS There are some other functions of possible interest. Described. Here. Now. @@ -2265,19 +2477,17 @@ class myclass { - ev_io io; void io_cb (ev::io &w, int revents); - ev_idle idle void idle_cb (ev::idle &w, int revents); - - myclass (); - } + ev::io io; void io_cb (ev::io &w, int revents); + ev:idle idle void idle_cb (ev::idle &w, int revents); - myclass::myclass (int fd) - { - io .set (this); - idle.set (this); + myclass (int fd) + { + io .set (this); + idle.set (this); - io.start (fd, ev::READ); - } + io.start (fd, ev::READ); + } + }; =head1 MACRO MAGIC @@ -2543,11 +2753,22 @@ interface to speed up C 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 watchers. + +In the absense of this define, libev will use C +(from F), which is usually good enough on most platforms. + =item EV_H The name of the F header file used to include it. The default if -undefined is C<"ev.h"> in F and F. This can be used to -virtually rename the F header file in case of conflicts. +undefined is C<"ev.h"> in F, F and F. This can be +used to virtually rename the F header file in case of conflicts. =item EV_CONFIG_H @@ -2558,7 +2779,7 @@ =item EV_EVENT_H Similarly to C, this macro can be used to override F's idea -of how the F header can be found, the dfeault is C<"event.h">. +of how the F header can be found, the default is C<"event.h">. =item EV_PROTOTYPES @@ -2619,6 +2840,11 @@ 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 @@ -2747,11 +2973,11 @@ 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)) @@ -2777,7 +3003,17 @@ 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 there were no other C +calls in the current loop iteration. Checking for async and signal events +involves iterating over all running async watchers or all signal numbers. =back