--- libev/ev.pod 2008/01/10 06:00:55 1.118 +++ libev/ev.pod 2008/04/09 22:07:50 1.145 @@ -8,49 +8,63 @@ =head2 EXAMPLE PROGRAM + // a single header file is required #include + // every watcher type has its own typedef'd struct + // with the name ev_ ev_io stdin_watcher; ev_timer timeout_watcher; - /* called when data readable on stdin */ + // all watcher callbacks have a similar signature + // this callback is called when data is readable on stdin static void stdin_cb (EV_P_ struct ev_io *w, int revents) { - /* puts ("stdin ready"); */ - ev_io_stop (EV_A_ w); /* just a syntax example */ - ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */ + puts ("stdin ready"); + // for one-shot events, one must manually stop the watcher + // with its corresponding stop function. + ev_io_stop (EV_A_ w); + + // this causes all nested ev_loop's to stop iterating + ev_unloop (EV_A_ EVUNLOOP_ALL); } + // another callback, this time for a time-out static void timeout_cb (EV_P_ struct ev_timer *w, int revents) { - /* puts ("timeout"); */ - ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ + puts ("timeout"); + // this causes the innermost ev_loop to stop iterating + ev_unloop (EV_A_ EVUNLOOP_ONE); } int main (void) { + // use the default event loop unless you have special needs struct ev_loop *loop = ev_default_loop (0); - /* initialise an io watcher, then start it */ + // initialise an io watcher, then start it + // this one will watch for stdin to become readable ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); ev_io_start (loop, &stdin_watcher); - /* simple non-repeating 5.5 second timeout */ + // initialise a timer watcher, then start it + // simple non-repeating 5.5 second timeout ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); ev_timer_start (loop, &timeout_watcher); - /* loop till timeout or data ready */ + // now wait for events to arrive ev_loop (loop, 0); + // unloop was called, so exit return 0; } =head1 DESCRIPTION -The newest version of this document is also available as a html-formatted +The newest version of this document is also available as an html-formatted web page you might find easier to navigate when reading it for the first time: L. @@ -86,12 +100,13 @@ =head2 CONVENTIONS -Libev is very configurable. In this manual the default configuration will -be described, which supports multiple event loops. For more info about -various configuration options please have a look at B section in -this manual. If libev was configured without support for multiple event -loops, then all functions taking an initial argument of name C -(which is always of type C) will not have this argument. +Libev is very configurable. In this manual the default (and most common) +configuration will be described, which supports multiple event loops. For +more info about various configuration options please have a look at +B section in this manual. If libev was configured without support +for multiple event loops, then all functions taking an initial argument of +name C (which is always of type C) will not have +this argument. =head2 TIME REPRESENTATION @@ -183,18 +198,21 @@ =item ev_set_allocator (void *(*cb)(void *ptr, long size)) Sets the allocation function to use (the prototype is similar - the -semantics is identical - to the realloc C function). It is used to -allocate and free memory (no surprises here). If it returns zero when -memory needs to be allocated, the library might abort or take some -potentially destructive action. The default is your system realloc -function. +semantics are identical to the C C89/SuS/POSIX function). It is +used to allocate and free memory (no surprises here). If it returns zero +when memory needs to be allocated (C), the library might abort +or take some potentially destructive action. + +Since some systems (at least OpenBSD and Darwin) fail to implement +correct C semantics, libev will use a wrapper around the system +C and C functions by default. You could override this function in high-availability programs to, say, free some memory if it cannot allocate memory, to use a special allocator, or even to sleep a while and retry until some memory is available. Example: Replace the libev allocator with one that waits a bit and then -retries). +retries (example requires a standards-compliant C). static void * persistent_realloc (void *ptr, size_t size) @@ -243,13 +261,6 @@ types of such loops, the I loop, which supports signals and child events, and dynamically created loops which do not. -If you use threads, a common model is to run the default event loop -in your main thread (or in a separate thread) and for each thread you -create, you also create another event loop. Libev itself does no locking -whatsoever, so if you mix calls to the same event loop in different -threads, make sure you lock (this is usually a bad idea, though, even if -done correctly, because it's hideous and inefficient). - =over 4 =item struct ev_loop *ev_default_loop (unsigned int flags) @@ -262,6 +273,10 @@ If you don't know what event loop to use, use the one returned from this function. +Note that this function is I thread-safe, so if you want to use it +from multiple threads, you have to lock (note also that this is unlikely, +as loops cannot bes hared easily between threads anyway). + 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 @@ -299,8 +314,8 @@ This works by calling C on every iteration of the loop, and thus this might slow down your event loop if you do a lot of loop iterations and little real work, but is usually not noticeable (on my -Linux system for example, C is actually a simple 5-insn sequence -without a syscall and thus I fast, but my Linux system also has +GNU/Linux system for example, C is actually a simple 5-insn sequence +without a syscall and thus I fast, but my GNU/Linux system also has C which is even faster). The big advantage of this flag is that you can forget about fork (and @@ -341,7 +356,7 @@ like O(total_fds) where n is the total number of fds (or the highest fd), epoll scales either O(1) or O(active_fds). The epoll design has a number of shortcomings, such as silently dropping events in some hard-to-detect -cases and rewiring a syscall per fd change, no fork support and bad +cases and requiring a syscall per fd change, no fork support and bad support for dup. While stopping, setting and starting an I/O watcher in the same iteration @@ -453,6 +468,10 @@ handle signal and child watchers, and attempts to do so will be greeted by undefined behaviour (or a failed assertion if assertions are enabled). +Note that this function I thread-safe, and the recommended way to use +libev with threads is indeed to create one loop per thread, and using the +default loop in the "main" or "initial" thread. + Example: Try to create a event loop that uses epoll and nothing else. struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); @@ -485,14 +504,16 @@ =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 @@ -500,16 +521,16 @@ 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 @@ -778,6 +799,10 @@ 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 @@ -1066,6 +1091,18 @@ enable C, or resort to C or C. +=head3 The special problem of SIGPIPE + +While not really specific to libev, it is easy to forget about SIGPIPE: +when reading from a pipe whose other end has been closed, your program +gets send a SIGPIPE, which, by default, aborts your program. For most +programs this is sensible behaviour, for daemons, this is usually +undesirable. + +So when you encounter spurious, unexplained daemon exits, make sure you +ignore SIGPIPE (and maybe make sure you log the exit status of your daemon +somewhere, as that would have given you a big clue). + =head3 Watcher-Specific Functions @@ -1152,7 +1189,7 @@ 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: @@ -1271,7 +1308,7 @@ 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) @@ -1415,6 +1452,12 @@ watcher for a signal is stopped libev will reset the signal handler to SIG_DFL (regardless of what it was set to before). +If possible and supported, libev will install its handlers with +C behaviour enabled, so syscalls should not be unduly +interrupted. If you have a problem with syscalls getting interrupted by +signals you can block all signals in an C watcher and unblock +them in an C watcher. + =head3 Watcher-Specific Functions and Data Members =over 4 @@ -1432,26 +1475,67 @@ =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] @@ -1470,17 +1554,32 @@ =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? @@ -1519,6 +1618,17 @@ usually detected immediately, and if the file exists there will be no polling. +=head3 ABI Issues (Largefile Support) + +Libev by default (unless the user overrides this) uses the default +compilation environment, which means that on systems with optionally +disabled large file support, you get the 32 bit version of the stat +structure. When using the library from programs that change the ABI to +use 64 bit file offsets the programs will fail. In that case you have to +compile libev with the same flags to get binary compatibility. This is +obviously the case with any flags that change the ABI, but the problem is +most noticably with ev_stat and largefile support. + =head3 Inotify When C support has been compiled into libev (generally only @@ -1570,7 +1680,7 @@ 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 @@ -1697,7 +1807,7 @@ { 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)); @@ -2048,6 +2158,151 @@ =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. + +=item bool = ev_async_pending (ev_async *) + +Returns a non-zero value when C has been called on the +watcher but the event has not yet been processed (or even noted) by the +event loop. + +C sets a flag in the watcher and wakes up the loop. When +the loop iterates next and checks for the watcher to have become active, +it will reset the flag again. C can be used to very +quickly check wether invoking the loop might be a good idea. + +Not that this does I check wether the watcher itself is pending, only +wether it has been requested to make this watcher pending. + +=back + + =head1 OTHER FUNCTIONS There are some other functions of possible interest. Described. Here. Now. @@ -2284,19 +2539,52 @@ class myclass { - ev_io io; void io_cb (ev::io &w, int revents); - ev_idle idle void idle_cb (ev::idle &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); - myclass (); - } + myclass (int fd) + { + io .set (this); + idle.set (this); - myclass::myclass (int fd) - { - io .set (this); - idle.set (this); + io.start (fd, ev::READ); + } + }; - io.start (fd, ev::READ); - } + +=head1 OTHER LANGUAGE BINDINGS + +Libev does not offer other language bindings itself, but bindings for a +numbe rof languages exist in the form of third-party packages. If you know +any interesting language binding in addition to the ones listed here, drop +me a note. + +=over 4 + +=item Perl + +The EV module implements the full libev API and is actually used to test +libev. EV is developed together with libev. Apart from the EV core module, +there are additional modules that implement libev-compatible interfaces +to C (C), C (C) and the +C event core (C and C). + +It can be found and installed via CPAN, its homepage is found at +L. + +=item Ruby + +Tony Arcieri has written a ruby extension that offers access to a subset +of the libev API and adds filehandle abstractions, asynchronous DNS and +more on top of it. It can be found via gem servers. Its homepage is at +L. + +=item D + +Leandro Lucarella has written a D language binding (F) for libev, to +be found at L. + +=back =head1 MACRO MAGIC @@ -2343,6 +2631,16 @@ Similar to the other two macros, this gives you the value of the default loop, if multiple loops are supported ("ev loop default"). +=item C, C + +Usage identical to C and C, but requires that the +default loop has been initialised (C == unchecked). Their behaviour +is undefined when the default loop has not been initialised by a previous +execution of C, C or C. + +It is often prudent to use C when initialising the first +watcher in a function but use C afterwards. + =back Example: Declare and initialise a check watcher, utilising the above @@ -2447,9 +2745,9 @@ =head2 PREPROCESSOR SYMBOLS/MACROS -Libev can be configured via a variety of preprocessor symbols you have to define -before including any of its files. The default is not to build for multiplicity -and only include the select backend. +Libev can be configured via a variety of preprocessor symbols you have to +define before including any of its files. The default in the absense of +autoconf is noted for every option. =over 4 @@ -2485,6 +2783,14 @@ If defined to be C<1>, libev will assume that C is available and will use it for delays. Otherwise it will use C