--- libev/ev.pod 2007/11/24 09:48:38 1.38 +++ libev/ev.pod 2007/11/27 19:41:52 1.52 @@ -50,7 +50,6 @@ to the C type in C, and when you need to do any calculations on it, you should treat it as such. - =head1 GLOBAL FUNCTIONS These functions can be called anytime, even before initialising the @@ -118,13 +117,13 @@ See the description of C watchers for more info. -=item ev_set_allocator (void *(*cb)(void *ptr, long size)) +=item ev_set_allocator (void *(*cb)(void *ptr, size_t size)) -Sets the allocation function to use (the prototype is similar to the -realloc C function, the semantics are identical). 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. +Sets the allocation function to use (the prototype and semantics are +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. You could override this function in high-availability programs to, say, free some memory if it cannot allocate memory, to use a special allocator, @@ -134,7 +133,7 @@ retries: better than mine). static void * - persistent_realloc (void *ptr, long size) + persistent_realloc (void *ptr, size_t size) { for (;;) { @@ -470,6 +469,7 @@ =back + =head1 ANATOMY OF A WATCHER A watcher is a structure that you create and register to record your @@ -546,6 +546,10 @@ The pid specified in the C watcher has received a status change. +=item C + +The path specified in the C watcher changed its attributes somehow. + =item C The C watcher has determined that you have nothing better to do. @@ -562,6 +566,15 @@ (for example, a C watcher might start an idle watcher to keep C from blocking). +=item C + +The embedded event loop specified in the C watcher needs attention. + +=item C + +The event loop has been resumed in the child process after fork (see +C). + =item C An unspecified error has occured, the watcher has been stopped. This might @@ -578,7 +591,7 @@ =back -=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS +=head2 GENERIC WATCHER FUNCTIONS In the following description, C stands for the watcher type, e.g. C for C watchers and C for C watchers. @@ -597,7 +610,7 @@ You can reinitialise a watcher at any time as long as it has been stopped (or never started) and there are no pending events outstanding. -The callbakc is always of type C. =item C (ev_TYPE *, [args]) @@ -690,16 +703,28 @@ =head1 WATCHER TYPES This section describes each watcher in detail, but will not repeat -information given in the last section. +information given in the last section. Any initialisation/set macros, +functions and members specific to the watcher type are explained. +Members are additionally marked with either I<[read-only]>, meaning that, +while the watcher is active, you can look at the member and expect some +sensible content, but you must not modify it (you can modify it while the +watcher is stopped to your hearts content), or I<[read-write]>, which +means you can expect it to have some sensible content while the watcher +is active, but you can also modify it. Modifying it may not do something +sensible or take immediate effect (or do anything at all), but libev will +not crash or malfunction in any way. -=head2 C - is this file descriptor readable or writable + +=head2 C - is this file descriptor readable or writable? I/O watchers check whether a file descriptor is readable or writable -in each iteration of the event loop (This behaviour is called -level-triggering because you keep receiving events as long as the -condition persists. Remember you can stop the watcher if you don't want to -act on the event and neither want to receive future events). +in each iteration of the event loop, or, more precisely, when reading +would not block the process and writing would at least be able to write +some data. This behaviour is called level-triggering because you keep +receiving events as long as the condition persists. Remember you can stop +the watcher if you don't want to act on the event and neither want to +receive future events. In general you can register as many read and/or write event watchers per fd as you want (as long as you don't confuse yourself). Setting all file @@ -709,33 +734,45 @@ You have to be careful with dup'ed file descriptors, though. Some backends (the linux epoll backend is a notable example) cannot handle dup'ed file descriptors correctly if you register interest in two or more fds pointing -to the same underlying file/socket etc. description (that is, they share +to the same underlying file/socket/etc. description (that is, they share the same underlying "file open"). If you must do this, then force the use of a known-to-be-good backend (at the time of this writing, this includes only C and 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 +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 +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 +wether 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). + =over 4 =item ev_io_init (ev_io *, callback, int fd, int events) =item ev_io_set (ev_io *, int fd, int events) -Configures an C watcher. The fd is the file descriptor to rceeive -events for and events is either C, C or C to receive the given events. - -Please note that most of the more scalable backend mechanisms (for example -epoll and solaris ports) can result in spurious readyness notifications -for file descriptors, so you practically need to use non-blocking I/O (and -treat callback invocation as hint only), or retest separately with a safe -interface before doing I/O (XLib can do this), or force the use of either -C or C, which don't suffer from this -problem. Also note that it is quite easy to have your callback invoked -when the readyness condition is no longer valid even when employing -typical ways of handling events, so its a good idea to use non-blocking -I/O unconditionally. +Configures an C watcher. The C is the file descriptor to +rceeive events for and events is either C, C or +C to receive the given events. + +=item int fd [read-only] + +The file descriptor being watched. + +=item int events [read-only] + +The events being watched. =back @@ -758,7 +795,7 @@ ev_loop (loop, 0); -=head2 C - relative and optionally recurring timeouts +=head2 C - relative and optionally repeating timeouts Timer watchers are simple relative timers that generate an event after a given time, and optionally repeating in regular intervals after that. @@ -809,13 +846,35 @@ value), or reset the running timer to the repeat 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 -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 after=repeat=60 and calling ev_timer_again each -time you successfully read or write some data. If you go into an idle -state where you do not expect data to travel on the socket, you can stop -the timer, and again will automatically restart it if need be. +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 C=C=C<60> and calling +C each time you successfully read or write some data. If +you go into an idle state where you do not expect data to travel on the +socket, you can stop the timer, and again will automatically restart it if +need be. + +You can also ignore the C value and C altogether +and only ever use the C value: + + ev_timer_init (timer, callback, 0., 5.); + ev_timer_again (loop, timer); + ... + timer->again = 17.; + ev_timer_again (loop, timer); + ... + timer->again = 10.; + ev_timer_again (loop, timer); + +This is more efficient then stopping/starting the timer eahc time you want +to modify its timeout value. + +=item ev_tstamp repeat [read-write] + +The current C value. Will be used each time the watcher times out +or C is called and determines the next timeout (if any), +which is also when any modifications are taken into account. =back @@ -850,7 +909,7 @@ ev_timer_again (&mytimer); -=head2 C - to cron or not to cron +=head2 C - to cron or not to cron? Periodic watchers are also timers of a kind, but they are very versatile (and unfortunately a bit complex). @@ -952,6 +1011,18 @@ 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 interval [read-write] + +The current interval value. Can be modified any time, but changes only +take effect when the periodic timer fires or C is being +called. + +=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write] + +The current reschedule callback, or C<0>, if this functionality is +switched off. Can be changed any time, but changes only take effect when +the periodic timer fires or C is being called. + =back Example: call a callback every hour, or, more precisely, whenever the @@ -988,7 +1059,7 @@ ev_periodic_start (loop, &hourly_tick); -=head2 C - signal me when a signal gets signalled +=head2 C - signal me when a signal gets signalled! Signal watchers will trigger an event when the process receives a specific signal one or more times. Even though signals are very asynchronous, libev @@ -1011,10 +1082,14 @@ Configures the watcher to trigger on the given signal number (usually one of the C constants). +=item int signum [read-only] + +The signal the watcher watches out for. + =back -=head2 C - wait for pid status changes +=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). @@ -1032,6 +1107,19 @@ C documentation). The C member contains the pid of the process causing the status change. +=item int pid [read-only] + +The process id this watcher watches out for, or C<0>, meaning any process id. + +=item int rpid [read-write] + +The process id that detected a status change. + +=item int rstatus [read-write] + +The process exit/trace status caused by C (see your systems +C and C documentation for details). + =back Example: try to exit cleanly on SIGINT and SIGTERM. @@ -1047,7 +1135,105 @@ ev_signal_start (loop, &sigint_cb); -=head2 C - when you've got nothing better to do +=head2 C - did the file attributes just change? + +This watches a filesystem 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. + +The path does not need to exist: changing from "path exists" to "path does +not exist" is a status change like any other. The condition "path does +not exist" is signified by the C field being zero (which is +otherwise always forced to be at least one) and all the other fields of +the stat buffer having unspecified contents. + +Since there is no standard to do this, the portable implementation simply +calls C regulalry on the path to see if it changed somehow. You +can specify a recommended polling interval for this case. If you specify +a polling interval of C<0> (highly recommended!) then a I value will be used (which you can expect to be around +five seconds, although this might change dynamically). Libev will also +impose a minimum interval which is currently around C<0.1>, but thats +usually overkill. + +This watcher type is not meant for massive numbers of stat watchers, +as even with OS-supported change notifications, this can be +resource-intensive. + +At the time of this writing, no specific OS backends are implemented, but +if demand increases, at least a kqueue and inotify backend will be added. + +=over 4 + +=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval) + +=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval) + +Configures the watcher to wait for status changes of the given +C. The C is a hint on how quickly a change is expected to +be detected and should normally be specified as C<0> to let libev choose +a suitable value. The memory pointed to by C must point to the same +path for as long as the watcher is active. + +The callback will be receive C 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 *) + +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. + +=item ev_statdata attr [read-only] + +The most-recently detected attributes of the file. Although the type is of +C, this is usually the (or one of the) C types +suitable for your system. If the C member is C<0>, then there +was some error while Cing the file. + +=item ev_statdata prev [read-only] + +The previous attributes of the file. The callback gets invoked whenever +C != C. + +=item ev_tstamp interval [read-only] + +The specified interval. + +=item const char *path [read-only] + +The filesystem path that is being watched. + +=back + +Example: Watch C for attribute changes. + + static void + passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) + { + /* /etc/passwd changed in some way */ + if (w->attr.st_nlink) + { + printf ("passwd current size %ld\n", (long)w->attr.st_size); + printf ("passwd current atime %ld\n", (long)w->attr.st_mtime); + printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime); + } + else + /* you shalt not abuse printf for puts */ + puts ("wow, /etc/passwd is not there, expect problems. " + "if this is windows, they already arrived\n"); + } + + ... + ev_stat passwd; + + ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); + ev_stat_start (loop, &passwd); + + +=head2 C - when you've got nothing better to do... Idle watchers trigger events when there are no other events are pending (prepare, check and other idle watchers do not count). That is, as long @@ -1091,16 +1277,27 @@ ev_idle_start (loop, idle_cb); -=head2 C and C - customise your event loop +=head2 C and C - customise your event loop! Prepare and check watchers are usually (but not always) used in tandem: prepare watchers get invoked before the process blocks and check watchers afterwards. +You I call C or similar functions that enter +the current event loop from either C or C +watchers. Other loops than the current one are fine, however. The +rationale behind this is that you do not need to check for recursion in +those watchers, i.e. the sequence will always be C, blocking, +C so if you have one watcher of each kind they will always be +called in pairs bracketing the blocking call. + Their main purpose is to integrate other event mechanisms into libev and their use is somewhat advanced. This could be used, for example, to track variable changes, implement your own watchers, integrate net-snmp or a -coroutine library and lots more. +coroutine library and lots more. They are also occasionally useful if +you cache some data and want to flush it before blocking (for example, +in X programs you might want to do an C in an C +watcher). This is done by examining in each prepare call which file descriptors need to be watched by the other library, registering C watchers for @@ -1132,10 +1329,63 @@ =back -Example: *TODO*. +Example: To include a library such as adns, you would add IO watchers +and a timeout watcher in a prepare handler, as required by libadns, and +in a check watcher, destroy them and call into libadns. What follows is +pseudo-code only of course: + + static ev_io iow [nfd]; + static ev_timer tw; + + static void + io_cb (ev_loop *loop, ev_io *w, int revents) + { + // set the relevant poll flags + // could also call adns_processreadable etc. here + struct pollfd *fd = (struct pollfd *)w->data; + if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; + if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; + } + + // create io watchers for each fd and a timer before blocking + static void + adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) + { + int timeout = 3600000;truct pollfd fds [nfd]; + // actual code will need to loop here and realloc etc. + adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); + + /* the callback is illegal, but won't be called as we stop during check */ + ev_timer_init (&tw, 0, timeout * 1e-3); + ev_timer_start (loop, &tw); + + // create on ev_io per pollfd + for (int i = 0; i < nfd; ++i) + { + ev_io_init (iow + i, io_cb, fds [i].fd, + ((fds [i].events & POLLIN ? EV_READ : 0) + | (fds [i].events & POLLOUT ? EV_WRITE : 0))); + + fds [i].revents = 0; + iow [i].data = fds + i; + ev_io_start (loop, iow + i); + } + } + + // stop all watchers after blocking + static void + adns_check_cb (ev_loop *loop, ev_check *w, int revents) + { + ev_timer_stop (loop, &tw); + + for (int i = 0; i < nfd; ++i) + ev_io_stop (loop, iow + i); + + adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); + } -=head2 C - when one backend isn't enough +=head2 C - when one backend isn't enough... This is a rather advanced watcher type that lets you embed one event loop into another (currently only C events are supported in the embedded @@ -1223,6 +1473,31 @@ similarly to C, but in the most apropriate way for embedded loops. +=item struct ev_loop *loop [read-only] + +The embedded event loop. + +=back + + +=head2 C - the audacity to resume the event loop after a fork + +Fork watchers are called when a C was detected (usually because +whoever is a good citizen cared to tell libev about it by calling +C or C). The invocation is done before the +event loop blocks next and before C watchers are being called, +and only in the child after the fork. If whoever good citizen calling +C cheats and calls it in the wrong process, the fork +handlers will be invoked, too, of course. + +=over 4 + +=item ev_fork_init (ev_signal *, callback) + +Initialises and configures the fork watcher - it has no parameters of any +kind. There is a C macro, but using it is utterly pointless, +believe me. + =back @@ -1394,6 +1669,10 @@ Invokes C. +=item w->update () C only + +Invokes C. + =back =back @@ -1416,6 +1695,396 @@ io.start (fd, ev::READ); } + +=head1 MACRO MAGIC + +Libev can be compiled with a variety of options, the most fundemantal is +C. This option determines wether (most) functions and +callbacks have an initial C argument. + +To make it easier to write programs that cope with either variant, the +following macros are defined: + +=over 4 + +=item C, C + +This provides the loop I for functions, if one is required ("ev +loop argument"). The C form is used when this is the sole argument, +C is used when other arguments are following. Example: + + ev_unref (EV_A); + ev_timer_add (EV_A_ watcher); + ev_loop (EV_A_ 0); + +It assumes the variable C of type C is in scope, +which is often provided by the following macro. + +=item C, C + +This provides the loop I for functions, if one is required ("ev +loop parameter"). The C form is used when this is the sole parameter, +C is used when other parameters are following. Example: + + // this is how ev_unref is being declared + static void ev_unref (EV_P); + + // this is how you can declare your typical callback + static void cb (EV_P_ ev_timer *w, int revents) + +It declares a parameter C of type C, quite +suitable for use with C. + +=item C, C + +Similar to the other two macros, this gives you the value of the default +loop, if multiple loops are supported ("ev loop default"). + +=back + +Example: Declare and initialise a check watcher, working regardless of +wether multiple loops are supported or not. + + static void + check_cb (EV_P_ ev_timer *w, int revents) + { + ev_check_stop (EV_A_ w); + } + + ev_check check; + ev_check_init (&check, check_cb); + ev_check_start (EV_DEFAULT_ &check); + ev_loop (EV_DEFAULT_ 0); + + +=head1 EMBEDDING + +Libev can (and often is) directly embedded into host +applications. Examples of applications that embed it include the Deliantra +Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe) +and rxvt-unicode. + +The goal is to enable you to just copy the neecssary files into your +source directory without having to change even a single line in them, so +you can easily upgrade by simply copying (or having a checked-out copy of +libev somewhere in your source tree). + +=head2 FILESETS + +Depending on what features you need you need to include one or more sets of files +in your app. + +=head3 CORE EVENT LOOP + +To include only the libev core (all the C functions), with manual +configuration (no autoconf): + + #define EV_STANDALONE 1 + #include "ev.c" + +This will automatically include F, too, and should be done in a +single C source file only to provide the function implementations. To use +it, do the same for F in all files wishing to use this API (best +done by writing a wrapper around F that you can include instead and +where you can put other configuration options): + + #define EV_STANDALONE 1 + #include "ev.h" + +Both header files and implementation files can be compiled with a C++ +compiler (at least, thats a stated goal, and breakage will be treated +as a bug). + +You need the following files in your source tree, or in a directory +in your include path (e.g. in libev/ when using -Ilibev): + + ev.h + ev.c + ev_vars.h + ev_wrap.h + + ev_win32.c required on win32 platforms only + + ev_select.c only when select backend is enabled (which is by default) + ev_poll.c only when poll backend is enabled (disabled by default) + ev_epoll.c only when the epoll backend is enabled (disabled by default) + ev_kqueue.c only when the kqueue backend is enabled (disabled by default) + ev_port.c only when the solaris port backend is enabled (disabled by default) + +F includes the backend files directly when enabled, so you only need +to compile this single file. + +=head3 LIBEVENT COMPATIBILITY API + +To include the libevent compatibility API, also include: + + #include "event.c" + +in the file including F, and: + + #include "event.h" + +in the files that want to use the libevent API. This also includes F. + +You need the following additional files for this: + + event.h + event.c + +=head3 AUTOCONF SUPPORT + +Instead of using C and providing your config in +whatever way you want, you can also C in your +F and leave C undefined. F will then +include F and configure itself accordingly. + +For this of course you need the m4 file: + + libev.m4 + +=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. + +=over 4 + +=item EV_STANDALONE + +Must always be C<1> if you do not use autoconf configuration, which +keeps libev from including F, and it also defines dummy +implementations for some libevent functions (such as logging, which is not +supported). It will also not define any of the structs usually found in +F that are not directly supported by the libev core alone. + +=item EV_USE_MONOTONIC + +If defined to be C<1>, libev will try to detect the availability of the +monotonic clock option at both compiletime and runtime. Otherwise no use +of the monotonic clock option will be attempted. If you enable this, you +usually have to link against librt or something similar. Enabling it when +the functionality isn't available is safe, though, althoguh you have +to make sure you link against any libraries where the C +function is hiding in (often F<-lrt>). + +=item EV_USE_REALTIME + +If defined to be C<1>, libev will try to detect the availability of the +realtime clock option at compiletime (and assume its availability at +runtime if successful). Otherwise no use of the realtime clock option will +be attempted. This effectively replaces C by C and will not normally affect correctness. See tzhe note about libraries +in the description of C, though. + +=item EV_USE_SELECT + +If undefined or defined to be C<1>, libev will compile in support for the +C