--- libev/ev.pod 2008/03/13 13:06:16 1.136 +++ libev/ev.pod 2008/06/09 14:11:30 1.167 @@ -4,69 +4,69 @@ =head1 SYNOPSIS - #include + #include =head2 EXAMPLE PROGRAM - // a single header file is required - #include + // 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; - - // 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"); - // 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"); - // 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 - // 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); - - // 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); - - // now wait for events to arrive - ev_loop (loop, 0); - - // unloop was called, so exit - return 0; - } + // every watcher type has its own typedef'd struct + // with the name ev_ + ev_io stdin_watcher; + ev_timer timeout_watcher; + + // 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"); + // 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"); + // 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 + // 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); + + // 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); + + // 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 an html-formatted web page you might find easier to navigate when reading it for the first -time: L. +time: L. Libev is an event loop: you register interest in certain events (such as a file descriptor being readable or a timeout occurring), and it will manage @@ -115,10 +115,31 @@ the beginning of 1970, details are complicated, don't ask). This type is called C, which is what you should use too. It usually aliases to the C type in C, and when you need to do any calculations on -it, you should treat it as some floatingpoint value. Unlike the name +it, you should treat it as some floating point value. Unlike the name component C might indicate, it is also used for time differences throughout libev. +=head1 ERROR HANDLING + +Libev knows three classes of errors: operating system errors, usage errors +and internal errors (bugs). + +When libev catches an operating system error it cannot handle (for example +a system call indicating a condition libev cannot fix), it calls the callback +set via C, which is supposed to fix the problem or +abort. The default is to print a diagnostic message and to call C. + +When libev detects a usage error such as a negative timer interval, then +it will print a diagnostic message and abort (via the C mechanism, +so C will disable this checking): these are programming errors in +the libev caller and need to be fixed there. + +Libev also has a few internal error-checking Cions, and also has +extensive consistency checking code. These do not trigger under normal +circumstances, as they indicate either a bug in libev or worse. + + =head1 GLOBAL FUNCTIONS These functions can be called anytime, even before initialising the @@ -136,7 +157,7 @@ Sleep for the given interval: The current thread will be blocked until either it is interrupted or the given time interval has passed. Basically -this is a subsecond-resolution C. +this is a sub-second-resolution C. =item int ev_version_major () @@ -159,9 +180,9 @@ Example: Make sure we haven't accidentally been linked against the wrong version. - assert (("libev version mismatch", - ev_version_major () == EV_VERSION_MAJOR - && ev_version_minor () >= EV_VERSION_MINOR)); + assert (("libev version mismatch", + ev_version_major () == EV_VERSION_MAJOR + && ev_version_minor () >= EV_VERSION_MINOR)); =item unsigned int ev_supported_backends () @@ -173,15 +194,15 @@ Example: make sure we have the epoll method, because yeah this is cool and a must have and can we have a torrent of it please!!!11 - assert (("sorry, no epoll, no sex", - ev_supported_backends () & EVBACKEND_EPOLL)); + assert (("sorry, no epoll, no sex", + ev_supported_backends () & EVBACKEND_EPOLL)); =item unsigned int ev_recommended_backends () Return the set of all backends compiled into this binary of libev and also recommended for this platform. This set is often smaller than the one returned by C, as for example kqueue is broken on -most BSDs and will not be autodetected unless you explicitly request it +most BSDs and will not be auto-detected unless you explicitly request it (assuming you know what you are doing). This is the set of backends that libev will probe for if you specify no backends explicitly. @@ -198,18 +219,21 @@ =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) @@ -230,10 +254,10 @@ =item ev_set_syserr_cb (void (*cb)(const char *msg)); -Set the callback function to call on a retryable syscall error (such +Set the callback function to call on a retryable system call error (such as failed select, poll, epoll_wait). The message is a printable string indicating the system call or subsystem causing the problem. If this -callback is set, then libev will expect it to remedy the sitution, no +callback is set, then libev will expect it to remedy the situation, no matter what, when it returns. That is, libev will generally retry the requested operation, or, if the condition doesn't go away, do bad stuff (such as abort). @@ -258,13 +282,6 @@ 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) @@ -277,9 +294,13 @@ 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 +for C. If this is a problem for your application 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. @@ -298,7 +319,7 @@ =item C -If this flag bit is ored into the flag value (or the program runs setuid +If this flag bit is or'ed into the flag value (or the program runs setuid or setgid) then libev will I look at the environment variable C. Otherwise (the default), this environment variable will override the flags completely if it is found in the environment. This is @@ -315,14 +336,14 @@ 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 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 +without a system call 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 forget about forgetting to tell libev about forking) when you use this flag. -This flag setting cannot be overriden or specified in the C +This flag setting cannot be overridden or specified in the C environment variable. =item C (value 1, portable select backend) @@ -334,11 +355,11 @@ usually the fastest backend for a low number of (low-numbered :) fds. To get good performance out of this backend you need a high amount of -parallelity (most of the file descriptors should be busy). If you are +parallelism (most of the file descriptors should be busy). If you are writing a server, you should C in a loop to accept as many connections as possible during one iteration. You might also want to have a look at C to increase the amount of -readyness notifications you get per iteration. +readiness notifications you get per iteration. =item C (value 2, poll backend, available everywhere except on windows) @@ -356,11 +377,11 @@ 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 system call per fd change, no fork support and bad support for dup. While stopping, setting and starting an I/O watcher in the same iteration -will result in some caching, there is still a syscall per such incident +will result in some caching, there is still a system call per such incident (because the fd could point to a different file description now), so its best to avoid that. Also, C'ed file descriptors might not work very well if you register events for both fds. @@ -373,7 +394,7 @@ watchers for a file descriptor until it has been closed, if possible, i.e. keep at least one watcher active per fd at all times. -While nominally embeddeble in other event loops, this feature is broken in +While nominally embeddable in other event loops, this feature is broken in all kernel versions tested so far. =item C (value 8, most BSD clones) @@ -381,7 +402,7 @@ Kqueue deserves special mention, as at the time of this writing, it was broken on all BSDs except NetBSD (usually it doesn't work reliably with anything but sockets and pipes, except on Darwin, where of course -it's completely useless). For this reason it's not being "autodetected" +it's completely useless). For this reason it's not being "auto-detected" unless you explicitly specify it explicitly in the flags (i.e. using C) or libev was compiled on a known-to-be-good (-enough) system like NetBSD. @@ -393,7 +414,7 @@ It scales in the same way as the epoll backend, but the interface to the kernel is more efficient (which says nothing about its actual speed, of course). While stopping, setting and starting an I/O watcher does never -cause an extra syscall as with C, it still adds up to +cause an extra system call as with C, it still adds up to two event changes per incident, support for C is very bad and it drops fds silently in similarly hard-to-detect cases. @@ -418,7 +439,7 @@ This uses the Solaris 10 event port mechanism. As with everything on Solaris, it's really slow, but it still scales very well (O(active_fds)). -Please note that solaris event ports can deliver a lot of spurious +Please note that Solaris event ports can deliver a lot of spurious notifications, so you need to use non-blocking I/O or other means to avoid blocking when no data (or space) is available. @@ -427,7 +448,7 @@ descriptors a "slow" C or C backend might perform better. -On the positive side, ignoring the spurious readyness notifications, this +On the positive side, ignoring the spurious readiness notifications, this backend actually performed to specification in all tests and is fully embeddable, which is a rare feat among the OS-specific backends. @@ -441,25 +462,25 @@ =back -If one or more of these are ored into the flags value, then only these +If one or more of these are or'ed into the flags value, then only these 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: - if (!ev_default_loop (0)) - fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); + if (!ev_default_loop (0)) + fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); Restrict libev to the select and poll backends, and do not allow environment settings to be taken into account: - ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); + ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); Use whatever libev has to offer, but make sure that kqueue is used if available (warning, breaks stuff, best use only with your own private event loop and only if you know the OS supports your types of fds): - ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); + ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); =item struct ev_loop *ev_loop_new (unsigned int flags) @@ -468,18 +489,22 @@ 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); - if (!epoller) - fatal ("no epoll found here, maybe it hides under your chair"); + struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); + if (!epoller) + fatal ("no epoll found here, maybe it hides under your chair"); =item ev_default_destroy () Destroys the default loop again (frees all memory and kernel state etc.). None of the active event watchers will be stopped in the normal sense, so e.g. C might still return true. It is your -responsibility to either stop all watchers cleanly yoursef I +responsibility to either stop all watchers cleanly yourself I calling this function, or cope with the fact afterwards (which is usually the easiest thing, you can just ignore the watchers and/or C them for example). @@ -570,7 +595,7 @@ case there are no events and will return after one iteration of the loop. A flags value of C will look for new events (waiting if -neccessary) and will handle those and any outstanding ones. It will block +necessary) and will handle those and any outstanding ones. It will block your process until at least one new event arrives, and will return after one iteration of the loop. This is useful if you are waiting for some external event in conjunction with something not expressible using other @@ -641,15 +666,15 @@ Example: Create a signal watcher, but keep it from keeping C running when nothing else is active. - struct ev_signal exitsig; - ev_signal_init (&exitsig, sig_cb, SIGINT); - ev_signal_start (loop, &exitsig); - evf_unref (loop); + struct ev_signal exitsig; + ev_signal_init (&exitsig, sig_cb, SIGINT); + ev_signal_start (loop, &exitsig); + evf_unref (loop); Example: For some weird reason, unregister the above signal handler again. - ev_ref (loop); - ev_signal_stop (loop, &exitsig); + ev_ref (loop); + ev_signal_stop (loop, &exitsig); =item ev_set_io_collect_interval (loop, ev_tstamp interval) @@ -681,11 +706,22 @@ will not be affected. Setting this to a non-null value will not introduce any overhead in libev. -Many (busy) programs can usually benefit by setting the io collect +Many (busy) programs can usually benefit by setting the I/O collect interval to a value near C<0.1> or so, which is often enough for interactive servers (of course not for games), likewise for timeouts. It usually doesn't make much sense to set it to a lower value than C<0.01>, -as this approsaches the timing granularity of most systems. +as this approaches the timing granularity of most systems. + +=item ev_loop_verify (loop) + +This function only does something when C support has been +compiled in. It tries to go through all internal structures and checks +them for validity. If anything is found to be inconsistent, it will print +an error message to standard error and call C. + +This can be used to catch bugs inside libev itself: under normal +circumstances, this function will never abort as of course libev keeps its +data structures consistent. =back @@ -696,18 +732,18 @@ interest in some event. For instance, if you want to wait for STDIN to become readable, you would create an C watcher for that: - static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) - { - ev_io_stop (w); - ev_unloop (loop, EVUNLOOP_ALL); - } - - struct ev_loop *loop = ev_default_loop (0); - struct ev_io stdin_watcher; - ev_init (&stdin_watcher, my_cb); - ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); - ev_io_start (loop, &stdin_watcher); - ev_loop (loop, 0); + static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) + { + ev_io_stop (w); + ev_unloop (loop, EVUNLOOP_ALL); + } + + struct ev_loop *loop = ev_default_loop (0); + struct ev_io stdin_watcher; + ev_init (&stdin_watcher, my_cb); + ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); + ev_io_start (loop, &stdin_watcher); + ev_loop (loop, 0); As you can see, you are responsible for allocating the memory for your watcher structures (and it is usually a bad idea to do this on the stack, @@ -715,7 +751,7 @@ Each watcher structure must be initialised by a call to C, which expects a callback to be provided. This -callback gets invoked each time the event occurs (or, in the case of io +callback gets invoked each time the event occurs (or, in the case of I/O watchers, each time the event loop detects that the file descriptor given is readable and/or writable). @@ -801,7 +837,7 @@ =item C -An unspecified error has occured, the watcher has been stopped. This might +An unspecified error has occurred, 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 problem. You best act on it by reporting the problem and somehow coping @@ -810,7 +846,7 @@ Libev will usually signal a few "dummy" events together with an error, for example it might indicate that a fd is readable or writable, and if your callbacks is well-written it can just attempt the operation and cope -with the error from read() or write(). This will not work in multithreaded +with the error from read() or write(). This will not work in multi-threaded programs, though, so beware. =back @@ -850,8 +886,8 @@ =item C (ev_TYPE *watcher, callback, [args]) -This convinience macro rolls both C and C macro -calls into a single call. This is the most convinient method to initialise +This convenience macro rolls both C and C macro +calls into a single call. This is the most convenient method to initialise a watcher. The same limitations apply, of course. =item C (loop *, ev_TYPE *watcher) @@ -944,22 +980,22 @@ member, you can also "subclass" the watcher type and provide your own data: - struct my_io - { - struct ev_io io; - int otherfd; - void *somedata; - struct whatever *mostinteresting; - } + struct my_io + { + struct ev_io io; + int otherfd; + void *somedata; + struct whatever *mostinteresting; + } And since your callback will be called with a pointer to the watcher, you can cast it back to your own type: - static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) - { - struct my_io *w = (struct my_io *)w_; - ... - } + static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) + { + struct my_io *w = (struct my_io *)w_; + ... + } More interesting and less C-conformant ways of casting your callback type instead have been omitted. @@ -967,31 +1003,31 @@ Another common scenario is having some data structure with multiple watchers: - struct my_biggy - { - int some_data; - ev_timer t1; - ev_timer t2; - } + struct my_biggy + { + int some_data; + ev_timer t1; + ev_timer t2; + } In this case getting the pointer to C is a bit more complicated, you need to use C: - #include + #include + + static void + t1_cb (EV_P_ struct ev_timer *w, int revents) + { + struct my_biggy big = (struct my_biggy * + (((char *)w) - offsetof (struct my_biggy, t1)); + } - static void - t1_cb (EV_P_ struct ev_timer *w, int revents) - { - struct my_biggy big = (struct my_biggy * - (((char *)w) - offsetof (struct my_biggy, t1)); - } - - static void - t2_cb (EV_P_ struct ev_timer *w, int revents) - { - struct my_biggy big = (struct my_biggy * - (((char *)w) - offsetof (struct my_biggy, t2)); - } + static void + t2_cb (EV_P_ struct ev_timer *w, int revents) + { + struct my_biggy big = (struct my_biggy * + (((char *)w) - offsetof (struct my_biggy, t2)); + } =head1 WATCHER TYPES @@ -1030,16 +1066,16 @@ C). Another thing you have to watch out for is that it is quite easy to -receive "spurious" readyness notifications, that is your callback might +receive "spurious" readiness notifications, that is your callback might be called with C but a subsequent C(2) will actually block because there is no data. Not only are some backends known to create a -lot of those (for example solaris ports), it is very easy to get into +lot of those (for example Solaris ports), it is very easy to get into this situation even with a relatively standard program structure. Thus it is best to always use non-blocking I/O: An extra C(2) returning C is far preferable to a program hanging until some data arrives. If you cannot run the fd in non-blocking mode (for example you should not -play around with an Xlib connection), then you have to seperately re-test +play around with an Xlib connection), then you have to separately re-test whether a file descriptor is really ready with a known-to-be good interface such as poll (fortunately in our Xlib example, Xlib already does this on its own, so its quite safe to use). @@ -1087,6 +1123,18 @@ 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 @@ -1097,7 +1145,7 @@ =item ev_io_set (ev_io *, int fd, int events) Configures an C watcher. The C is the file descriptor to -rceeive events for and events is either C, C or +receive events for and events is either C, C or C to receive the given events. =item int fd [read-only] @@ -1116,19 +1164,19 @@ readable, but only once. Since it is likely line-buffered, you could attempt to read a whole line in the callback. - static void - stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) - { - ev_io_stop (loop, w); - .. read from stdin here (or from w->fd) and haqndle any I/O errors - } - - ... - struct ev_loop *loop = ev_default_init (0); - struct ev_io stdin_readable; - ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); - ev_io_start (loop, &stdin_readable); - ev_loop (loop, 0); + static void + stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) + { + ev_io_stop (loop, w); + .. read from stdin here (or from w->fd) and haqndle any I/O errors + } + + ... + struct ev_loop *loop = ev_default_init (0); + struct ev_io stdin_readable; + ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); + ev_io_start (loop, &stdin_readable); + ev_loop (loop, 0); =head2 C - relative and optionally repeating timeouts @@ -1137,8 +1185,8 @@ given time, and optionally repeating in regular intervals after that. The timers are based on real time, that is, if you register an event that -times out after an hour and you reset your system clock to last years -time, it will still time out after (roughly) and hour. "Roughly" because +times out after an hour and you reset your system clock to January last +year, it will still time out after (roughly) and hour. "Roughly" because detecting time jumps is hard, and some inaccuracies are unavoidable (the monotonic clock option helps a lot here). @@ -1150,7 +1198,7 @@ ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); -The callback is guarenteed to be invoked only when its timeout has passed, +The callback is guaranteed to be invoked only after its timeout has passed, but if multiple timers become ready during the same loop iteration then order of execution is undefined. @@ -1162,16 +1210,17 @@ =item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) -Configure the timer to trigger after C seconds. If C is -C<0.>, then it will automatically be stopped. If it is positive, then the -timer will automatically be configured to trigger again C seconds -later, again, and again, until stopped manually. - -The timer itself will do a best-effort at avoiding drift, that is, if you -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. +Configure the timer to trigger after C seconds. If C +is C<0.>, then it will automatically be stopped once the timeout is +reached. If it is positive, then the timer will automatically be +configured to trigger again C seconds later, again, and again, +until stopped manually. + +The timer itself will do a best-effort at avoiding drift, that is, if +you configure a timer to trigger every 10 seconds, then it will normally +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, ev_timer *) @@ -1180,13 +1229,13 @@ If the timer is pending, its pending status is cleared. -If the timer is started but nonrepeating, stop it (as if it timed out). +If the timer is started but non-repeating, stop it (as if it timed out). If the timer is repeating, either start it if necessary (with the C value), or reset the running timer to the C value. This sounds a bit complicated, but here is a useful and typical -example: Imagine you have a tcp connection and you want a so-called idle +example: Imagine you have a TCP connection and you want a so-called idle timeout, that is, you want to be called when there have been, say, 60 seconds of inactivity on the socket. The easiest way to do this is to configure an C with a C value of C<60> and then call @@ -1222,33 +1271,33 @@ Example: Create a timer that fires after 60 seconds. - static void - one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) - { - .. one minute over, w is actually stopped right here - } - - struct ev_timer mytimer; - ev_timer_init (&mytimer, one_minute_cb, 60., 0.); - ev_timer_start (loop, &mytimer); + static void + one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + { + .. one minute over, w is actually stopped right here + } + + struct ev_timer mytimer; + ev_timer_init (&mytimer, one_minute_cb, 60., 0.); + ev_timer_start (loop, &mytimer); Example: Create a timeout timer that times out after 10 seconds of inactivity. - static void - timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) - { - .. ten seconds without any activity - } - - struct ev_timer mytimer; - ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ - ev_timer_again (&mytimer); /* start timer */ - ev_loop (loop, 0); - - // and in some piece of code that gets executed on any "activity": - // reset the timeout to start ticking again at 10 seconds - ev_timer_again (&mytimer); + static void + timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) + { + .. ten seconds without any activity + } + + struct ev_timer mytimer; + ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ + ev_timer_again (&mytimer); /* start timer */ + ev_loop (loop, 0); + + // and in some piece of code that gets executed on any "activity": + // reset the timeout to start ticking again at 10 seconds + ev_timer_again (&mytimer); =head2 C - to cron or not to cron? @@ -1257,19 +1306,20 @@ (and unfortunately a bit complex). Unlike C's, they are not based on real time (or relative time) -but on wallclock time (absolute time). You can tell a periodic watcher -to trigger "at" some specific point in time. For example, if you tell a -periodic watcher to trigger in 10 seconds (by specifiying e.g. C) and then reset your system clock to the last year, then it will -take a year to trigger the event (unlike an C, which would trigger -roughly 10 seconds later). - -They can also be used to implement vastly more complex timers, such as -triggering an event on each midnight, local time or other, complicated, -rules. +but on wall clock time (absolute time). You can tell a periodic watcher +to trigger after some specific point in time. For example, if you tell a +periodic watcher to trigger in 10 seconds (by specifying e.g. C, that is, an absolute time not a delay) and then reset your system +clock to January of the previous year, then it will take more than year +to trigger the event (unlike an C, which would still trigger +roughly 10 seconds later as it uses a relative timeout). + +Cs can also be used to implement vastly more complex timers, +such as triggering an event on each "midnight, local time", or other +complicated, rules. -As with timers, the callback is guarenteed to be invoked only when the -time (C) has been passed, but if multiple periodic timers become ready +As with timers, the callback is guaranteed to be invoked only when the +time (C) has passed, but if multiple periodic timers become ready during the same loop iteration then order of execution is undefined. =head3 Watcher-Specific Functions and Data Members @@ -1287,10 +1337,10 @@ =item * absolute timer (at = time, interval = reschedule_cb = 0) -In this configuration the watcher triggers an event at the wallclock time -C 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. +In this configuration the watcher triggers an event after the wall clock +time C has passed 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 * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) @@ -1299,12 +1349,13 @@ and then repeat, regardless of any time jumps. This can be used to create timers that do not drift with respect to system -time: +time, for example, here is a C that triggers each hour, on +the hour: ev_periodic_set (&periodic, 0., 3600., 0); This doesn't mean there will always be 3600 seconds in between triggers, -but only that the the callback will be called when the system time shows a +but only that the callback will be called when the system time shows a full hour (UTC), or more correctly, when the system time is evenly divisible by 3600. @@ -1314,7 +1365,12 @@ For numerical stability it is preferable that the C value is near C (the current time), but there is no range requirement for -this value. +this value, and in fact is often specified as zero. + +Note also that there is an upper limit to how often a timer can fire (CPU +speed for example), so if C is very small then timing stability +will of course deteriorate. Libev itself tries to be exact to be about one +millisecond (if the OS supports it and the machine is fast enough). =item * manual reschedule mode (at and interval ignored, reschedule_cb = callback) @@ -1324,12 +1380,14 @@ current time as second argument. NOTE: I. If you need to stop it, -return C (or so, fudge fudge) and stop it afterwards (e.g. by -starting an C watcher, which is legal). +ever, or make ANY event loop modifications whatsoever>. -Its prototype is C, e.g.: +If you need to stop it, return C (or so, fudge fudge) and stop +it afterwards (e.g. by starting an C watcher, which is the +only event loop modification you are allowed to do). + +The callback prototype is C, e.g.: static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) { @@ -1341,11 +1399,11 @@ will usually be called just before the callback will be triggered, but might be called at other times, too. -NOTE: I<< This callback must always return a time that is later than the -passed C value >>. Not even C itself will do, it I be larger. +NOTE: I<< This callback must always return a time that is higher than or +equal to the passed C value >>. This can be used to create very complex timers, such as a timer that -triggers on each midnight, local time. To do this, you would calculate the +triggers on "next midnight, local time". To do this, you would calculate the next midnight after C and return the timestamp value for this. How you do this is, again, up to you (but it is not trivial, which is the main reason I omitted it as an example). @@ -1359,6 +1417,11 @@ a different time than the last time it was called (e.g. in a crond like program when the crontabs have changed). +=item ev_tstamp ev_periodic_at (ev_periodic *) + +When active, returns the absolute time that the watcher is supposed to +trigger next. + =item ev_tstamp offset [read-write] When repeating, this contains the offset value, otherwise this is the @@ -1379,47 +1442,42 @@ switched off. Can be changed any time, but changes only take effect when the periodic timer fires or C is being called. -=item ev_tstamp at [read-only] - -When active, contains the absolute time that the watcher is supposed to -trigger next. - =back =head3 Examples Example: Call a callback every hour, or, more precisely, whenever the system clock is divisible by 3600. The callback invocation times have -potentially a lot of jittering, but good long-term stability. +potentially a lot of jitter, but good long-term stability. - static void - clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) - { - ... its now a full hour (UTC, or TAI or whatever your clock follows) - } - - struct ev_periodic hourly_tick; - ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); - ev_periodic_start (loop, &hourly_tick); + static void + clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) + { + ... its now a full hour (UTC, or TAI or whatever your clock follows) + } + + struct ev_periodic hourly_tick; + ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); + ev_periodic_start (loop, &hourly_tick); Example: The same as above, but use a reschedule callback to do it: - #include + #include - static ev_tstamp - my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) - { - return fmod (now, 3600.) + 3600.; - } + static ev_tstamp + my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) + { + return fmod (now, 3600.) + 3600.; + } - ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); + ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); Example: Call a callback every hour, starting now: - struct ev_periodic hourly_tick; - ev_periodic_init (&hourly_tick, clock_cb, - fmod (ev_now (loop), 3600.), 3600., 0); - ev_periodic_start (loop, &hourly_tick); + struct ev_periodic hourly_tick; + ev_periodic_init (&hourly_tick, clock_cb, + fmod (ev_now (loop), 3600.), 3600., 0); + ev_periodic_start (loop, &hourly_tick); =head2 C - signal me when a signal gets signalled! @@ -1437,8 +1495,8 @@ 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 +C behaviour enabled, so system calls should not be unduly +interrupted. If you have a problem with system calls getting interrupted by signals you can block all signals in an C watcher and unblock them in an C watcher. @@ -1463,15 +1521,15 @@ 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); + 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 @@ -1483,13 +1541,13 @@ 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. +you can only register 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 +the first child watcher is started after the child exits. The occurrence 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. @@ -1541,34 +1599,34 @@ Example: C a new process and install a child handler to wait for its completion. - ev_child cw; + ev_child cw; + + static void + child_cb (EV_P_ struct ev_child *w, int revents) + { + ev_child_stop (EV_A_ w); + printf ("process %d exited with status %x\n", w->rpid, w->rstatus); + } + + pid_t pid = fork (); - static void - child_cb (EV_P_ struct ev_child *w, int revents) - { - ev_child_stop (EV_A_ w); - printf ("process %d exited with status %x\n", w->rpid, w->rstatus); - } - - 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); - } + 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? -This watches a filesystem path for attribute changes. That is, it calls +This watches a file system path for attribute changes. That is, it calls C regularly (or when the OS says it changed) and sees if it changed compared to the last time, invoking the callback if it did. @@ -1596,11 +1654,23 @@ At the time of this writing, only the Linux inotify interface is implemented (implementing kqueue support is left as an exercise for the -reader). Inotify will be used to give hints only and should not change the -semantics of C watchers, which means that libev sometimes needs -to fall back to regular polling again even with inotify, but changes are -usually detected immediately, and if the file exists there will be no -polling. +reader, note, however, that the author sees no way of implementing ev_stat +semantics with kqueue). Inotify will be used to give hints only and should +not change the semantics of C watchers, which means that libev +sometimes needs to fall back to regular polling again even with inotify, +but changes are 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 noticeably with ev_stat and large file support. =head3 Inotify @@ -1609,9 +1679,9 @@ change detection where possible. The inotify descriptor will be created lazily when the first C watcher is being started. -Inotify presense does not change the semantics of C watchers +Inotify presence does not change the semantics of C watchers except that changes might be detected earlier, and in some cases, to avoid -making regular C calls. Even in the presense of inotify support +making regular C calls. Even in the presence of inotify support there are many cases where libev has to resort to regular C polling. (There is no support for kqueue, as apparently it cannot be used to @@ -1620,20 +1690,29 @@ =head3 The special problem of stat time resolution -The C syscall only supports full-second resolution portably, and -even on systems where the resolution is higher, many filesystems still +The C system call only supports full-second resolution portably, and +even on systems where the resolution is higher, many file systems still only support whole seconds. -That means that, if the time is the only thing that changes, you might -miss updates: on the first update, C detects a change and calls -your callback, which does something. When there is another update within -the same second, C will be unable to detect it. - -The solution to this is to delay acting on a change for a second (or till -the next second boundary), using a roughly one-second delay C -(C). The C<.01> -is added to work around small timing inconsistencies of some operating -systems. +That means that, if the time is the only thing that changes, you can +easily miss updates: on the first update, C detects a change and +calls your callback, which does something. When there is another update +within the same second, C will be unable to detect it as the stat +data does not change. + +The solution to this is to delay acting on a change for slightly more +than a second (or till slightly after the next full second boundary), using +a roughly one-second-delay C (e.g. C). + +The C<.02> offset is added to work around small timing inconsistencies +of some operating systems (where the second counter of the current time +might be be delayed. One such system is the Linux kernel, where a call to +C might return a timestamp with a full second later than +a subsequent C