ev_periodic - to cron or not to cron?ev_signal - signal me when a signal gets signalled!ev_child - watch out for process status changesev_stat - did the file attributes just change?ev_idle - when you've got nothing better to do...ev_prepare and ev_check - customise your event loop!ev_embed - when one backend isn't enough...ev_fork - the audacity to resume the event loop after a fork#include <ev.h> +/* this is the only header you need */ + #include <ev.h> + + /* what follows is a fully working example program */ + ev_io stdin_watcher; + ev_timer timeout_watcher; + + /* called when data 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 */ + } + + static void + timeout_cb (EV_P_ struct ev_timer *w, int revents) + { + /* puts ("timeout"); */ + ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */ + } + + int + main (void) + { + struct ev_loop *loop = ev_default_loop (0); + + /* initialise an io watcher, then start it */ + 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 */ + ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); + ev_timer_start (loop, &timeout_watcher); + + /* loop till timeout or data ready */ + ev_loop (loop, 0); + + return 0; + }@@ -114,10 +158,6 @@ calledev_tstamp, which is what you should use too. It usually alia to thedoubletype in C, and when you need to do any calculations on it, you should treat it as such. - - - -
See the description of ev_embed watchers for more info.
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, 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: better than mine).
static void *
- persistent_realloc (void *ptr, long size)
+ persistent_realloc (void *ptr, size_t size)
{
for (;;)
{
@@ -587,6 +627,10 @@ writable.
The pid specified in the ev_child watcher has received a status change.
EV_STATThe path specified in the ev_stat watcher changed its attributes somehow.
EV_IDLEThe ev_idle watcher has determined that you have nothing better to do.
ev_prepare watcher might start an idle watcher to keep
ev_loop from blocking).
+ EV_EMBEDThe embedded event loop specified in the ev_embed watcher needs attention.
EV_FORKThe event loop has been resumed in the child process after fork (see
+ev_fork).
EV_ERRORThis 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 [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 [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.
@@ -782,6 +844,14 @@ its own, so its quite safe to use). rceeive events for and events is eitherEV_READ, EV_WRITE or
EV_READ | EV_WRITE to receive the given events.
+ The file descriptor being watched.
+The events being watched.
+Example: call stdin_readable_cb when STDIN_FILENO has become, well
readable, but only once. Since it is likely line-buffered, you could
@@ -848,13 +918,34 @@ repeating. The exact semantics are:
If the timer is repeating, either start it if necessary (with the repeat 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 ev_timer 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.
ev_timer 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.
+ You can also ignore the after value and ev_timer_start altogether
+and only ever use the repeat 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.
+ +The current repeat value. Will be used each time the watcher times out
+or ev_timer_again is called and determines the next timeout (if any),
+which is also when any modifications are taken into account.
Example: create a timer that fires after 60 seconds.
@@ -982,6 +1073,18 @@ when you changed some parameters or the reschedule callback would return a different time than the last time it was called (e.g. in a crond like program when the crontabs have changed). +The current interval value. Can be modified any time, but changes only
+take effect when the periodic timer fires or ev_periodic_again is being
+called.
The current reschedule callback, or 0, if this functionality is
+switched off. Can be changed any time, but changes only take effect when
+the periodic timer fires or ev_periodic_again is being called.
Example: call a callback every hour, or, more precisely, whenever the system clock is divisible by 3600. The callback invocation times have @@ -1040,6 +1143,10 @@ SIG_DFL (regardless of what it was set to before).
Configures the watcher to trigger on the given signal number (usually one
of the SIGxxx constants).
The signal the watcher watches out for.
+sys/wait.h and see your system
waitpid documentation). The rpid member contains the pid of the
process causing the status change.
+ The process id this watcher watches out for, or 0, meaning any process id.
The process id that detected a status change.
+The process exit/trace status caused by rpid (see your systems
+waitpid and sys/wait.h documentation for details).
Example: try to exit cleanly on SIGINT and SIGTERM.
static void @@ -1077,6 +1197,99 @@ process causing the status change. ++ +
ev_stat - did the file attributes just change?This watches a filesystem path for attribute changes. That is, it calls
+stat 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 st_nlink 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 stat (2) 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 0 (highly recommended!) then a suitable,
+unspecified default 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 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.
+Configures the watcher to wait for status changes of the given
+path. The interval is a hint on how quickly a change is expected to
+be detected and should normally be specified as 0 to let libev choose
+a suitable value. The memory pointed to by path must point to the same
+path for as long as the watcher is active.
The callback will be receive EV_STAT when a change was detected,
+relative to the attributes at the time the watcher was started (or the
+last change was detected).
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.
+The most-recently detected attributes of the file. Although the type is of
+ev_statdata, this is usually the (or one of the) struct stat types
+suitable for your system. If the st_nlink member is 0, then there
+was some error while stating the file.
The previous attributes of the file. The callback gets invoked whenever
+prev != attr.
The specified interval.
+The filesystem path that is being watched.
+Example: Watch /etc/passwd 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);
+
+
+
+
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 must not call ev_loop or similar functions that enter
+the current event loop from either ev_prepare or ev_check
+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 ev_prepare, blocking,
+ev_check 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 anXFlush () in an ev_prepare
+watcher).
This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering ev_io watchers for
them and starting an ev_timer watcher for any timeouts (many libraries
@@ -1157,12 +1380,65 @@ parameters of any kind. There are ev_prepare_set and ev_check
macros, but using them is utterly, utterly and completely pointless.
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));
+ }
+
+
ev_embed - when one backend isn't enough...ev_loop (embedded_loop, EVLOOP_NONBLOCK), but in the most
apropriate way for embedded loops.
+ The embedded event loop.
+ev_fork - the audacity to resume the event loop after a forkFork watchers are called when a fork () was detected (usually because
+whoever is a good citizen cared to tell libev about it by calling
+ev_default_fork or ev_loop_fork). The invocation is done before the
+event loop blocks next and before ev_check watchers are being called,
+and only in the child after the fork. If whoever good citizen calling
+ev_default_fork cheats and calls it in the wrong process, the fork
+handlers will be invoked, too, of course.
Initialises and configures the fork watcher - it has no parameters of any
+kind. There is a ev_fork_set macro, but using it is utterly pointless,
+believe me.
Invokes ev_embed_sweep.
ev::stat onlyInvokes ev_stat_stat.
Libev can be compiled with a variety of options, the most fundemantal is
+EV_MULTIPLICITY. This option determines wether (most) functions and
+callbacks have an initial struct ev_loop * argument.
To make it easier to write programs that cope with either variant, the +following macros are defined:
+EV_A, EV_A_This provides the loop argument for functions, if one is required ("ev
+loop argument"). The EV_A form is used when this is the sole argument,
+EV_A_ 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 loop of type struct ev_loop * is in scope,
+which is often provided by the following macro.
EV_P, EV_P_This provides the loop parameter for functions, if one is required ("ev
+loop parameter"). The EV_P form is used when this is the sole parameter,
+EV_P_ 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 loop of type struct ev_loop *, quite
+suitable for use with EV_A.
EV_DEFAULT, EV_DEFAULT_Similar to the other two macros, this gives you the value of the default +loop, if multiple loops are supported ("ev loop default").
+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);
+
+
+
+
If undefined or defined to be 1, then periodic timers are supported,
-otherwise not. This saves a few kb of code.
If undefined or defined to be 1, then periodic timers are supported. If
+defined to be 0, then they are not. Disabling them saves a few kB of
+code.
If undefined or defined to be 1, then embed watchers are supported. If
+defined to be 0, then they are not.
If undefined or defined to be 1, then stat watchers are supported. If
+defined to be 0, then they are not.
If undefined or defined to be 1, then fork watchers are supported. If
+defined to be 0, then they are not.
If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to 1. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.
ev_child watchers use a small hash table to distribute workload by
+pid. The default size is 16 (or 1 with EV_MINIMAL), usually more
+than enough. If you need to manage thousands of children you might want to
+increase this value.
Can be used to change the callback member declaration in each watcher, and the way callbacks are invoked and set. Must expand to a struct member definition and a statement, respectively. See the ev.v header file for their default definitions. One possible use for overriding these is to -avoid the ev_loop pointer as first argument in all cases, or to use method -calls instead of plain function calls in C++.
+avoid thestruct ev_loop * as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
#include "ev_cpp.h" #include "ev.c" + + ++ +
In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for ev_default_init.
+