X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/73ce65a9122dd90fac253802fe20630572fdd4be..b7e58d7ed7f85d7cb7fe1c34cfe3fa2484a6dc31:/ev.pod diff --git a/ev.pod b/ev.pod index 5440be5..3f4a064 100644 --- a/ev.pod +++ b/ev.pod @@ -470,6 +470,7 @@ Example: for some weird reason, unregister the above signal handler again. =back + =head1 ANATOMY OF A WATCHER A watcher is a structure that you create and register to record your @@ -578,7 +579,7 @@ programs, though, so beware. =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 +598,7 @@ which rolls both calls into one. 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]) @@ -693,13 +694,15 @@ This section describes each watcher in detail, but will not repeat information given in the last section. -=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 +712,37 @@ required if you know what you are doing). 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. =back @@ -758,7 +765,7 @@ attempt to read a whole line in the callback: 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. @@ -850,7 +857,7 @@ inactivity. 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). @@ -988,7 +995,7 @@ Example: call a callback every hour, starting now: 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 @@ -1014,7 +1021,7 @@ of the C constants). =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). @@ -1047,7 +1054,7 @@ Example: try to exit cleanly on SIGINT and SIGTERM. ev_signal_start (loop, &sigint_cb); -=head2 C - when you've got nothing better to do +=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 +1098,27 @@ callback, free it. Alos, use no error checking, as usual. 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 +1150,63 @@ macros, but using them is utterly, utterly and completely pointless. =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); -=head2 C - when one backend isn't enough + adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); + } + + +=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 @@ -1416,6 +1487,322 @@ the constructor. io.start (fd, ev::READ); } +=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