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@ -175,7 +175,8 @@ Libev represents time as a single floating point number, representing the |
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(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near |
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the beginning of 1970, details are complicated, don't ask). This type is |
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called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases |
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to the double type in C. |
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to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on |
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it, you should treat it as such. |
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.SH "GLOBAL FUNCTIONS" |
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.IX Header "GLOBAL FUNCTIONS" |
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These functions can be called anytime, even before initialising the |
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@ -201,12 +202,29 @@ Usually, it's a good idea to terminate if the major versions mismatch, |
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as this indicates an incompatible change. Minor versions are usually |
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compatible to older versions, so a larger minor version alone is usually |
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not a problem. |
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.Sp |
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Example: make sure we haven't accidentally been linked against the wrong |
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version: |
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.Sp |
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.Vb 3 |
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\& assert (("libev version mismatch", |
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\& ev_version_major () == EV_VERSION_MAJOR |
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\& && ev_version_minor () >= EV_VERSION_MINOR)); |
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.Ve |
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.IP "unsigned int ev_supported_backends ()" 4 |
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.IX Item "unsigned int ev_supported_backends ()" |
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Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR |
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value) compiled into this binary of libev (independent of their |
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availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for |
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a description of the set values. |
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.Sp |
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Example: make sure we have the epoll method, because yeah this is cool and |
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a must have and can we have a torrent of it please!!!11 |
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.Sp |
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.Vb 2 |
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\& assert (("sorry, no epoll, no sex", |
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\& ev_supported_backends () & EVBACKEND_EPOLL)); |
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.Ve |
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.IP "unsigned int ev_recommended_backends ()" 4 |
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.IX Item "unsigned int ev_recommended_backends ()" |
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Return the set of all backends compiled into this binary of libev and also |
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@ -226,6 +244,34 @@ destructive action. The default is your system realloc function. |
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You could override this function in high-availability programs to, say, |
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free some memory if it cannot allocate memory, to use a special allocator, |
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or even to sleep a while and retry until some memory is available. |
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.Sp |
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Example: replace the libev allocator with one that waits a bit and then |
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retries: better than mine). |
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.Sp |
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.Vb 6 |
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\& static void * |
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\& persistent_realloc (void *ptr, long size) |
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\& { |
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\& for (;;) |
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\& { |
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\& void *newptr = realloc (ptr, size); |
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.Ve |
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.Sp |
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.Vb 2 |
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\& if (newptr) |
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\& return newptr; |
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.Ve |
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.Sp |
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.Vb 3 |
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\& sleep (60); |
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\& } |
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\& } |
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.Ve |
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.Sp |
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.Vb 2 |
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\& ... |
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\& ev_set_allocator (persistent_realloc); |
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.Ve |
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.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 |
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.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" |
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Set the callback function to call on a retryable syscall error (such |
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@ -235,6 +281,22 @@ callback is set, then libev will expect it to remedy the sitution, no |
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matter what, when it returns. That is, libev will generally retry the |
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requested operation, or, if the condition doesn't go away, do bad stuff |
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(such as abort). |
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.Sp |
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Example: do the same thing as libev does internally: |
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.Sp |
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.Vb 6 |
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\& static void |
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\& fatal_error (const char *msg) |
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\& { |
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\& perror (msg); |
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\& abort (); |
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\& } |
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.Ve |
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.Sp |
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.Vb 2 |
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\& ... |
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\& ev_set_syserr_cb (fatal_error); |
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.Ve |
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.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" |
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.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" |
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An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two |
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@ -378,6 +440,14 @@ Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loo |
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always distinct from the default loop. Unlike the default loop, it cannot |
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handle signal and child watchers, and attempts to do so will be greeted by |
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undefined behaviour (or a failed assertion if assertions are enabled). |
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.Sp |
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Example: try to create a event loop that uses epoll and nothing else. |
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.Sp |
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.Vb 3 |
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\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); |
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\& if (!epoller) |
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\& fatal ("no epoll found here, maybe it hides under your chair"); |
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.Ve |
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.IP "ev_default_destroy ()" 4 |
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.IX Item "ev_default_destroy ()" |
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Destroys the default loop again (frees all memory and kernel state |
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@ -421,10 +491,10 @@ use. |
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.IP "ev_tstamp ev_now (loop)" 4 |
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.IX Item "ev_tstamp ev_now (loop)" |
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Returns the current \*(L"event loop time\*(R", which is the time the event loop |
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got events and started processing them. This timestamp does not change |
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as long as callbacks are being processed, and this is also the base time |
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used for relative timers. You can treat it as the timestamp of the event |
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occuring (or more correctly, the mainloop finding out about it). |
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received events and started processing them. This timestamp does not |
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change as long as callbacks are being processed, and this is also the base |
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time used for relative timers. You can treat it as the timestamp of the |
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event occuring (or more correctly, libev finding out about it). |
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.IP "ev_loop (loop, int flags)" 4 |
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.IX Item "ev_loop (loop, int flags)" |
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Finally, this is it, the event handler. This function usually is called |
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@ -434,6 +504,12 @@ events. |
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If the flags argument is specified as \f(CW0\fR, it will not return until |
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either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. |
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.Sp |
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Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than |
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relying on all watchers to be stopped when deciding when a program has |
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finished (especially in interactive programs), but having a program that |
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automatically loops as long as it has to and no longer by virtue of |
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relying on its watchers stopping correctly is a thing of beauty. |
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.Sp |
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A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle |
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those events and any outstanding ones, but will not block your process in |
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case there are no events and will return after one iteration of the loop. |
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@ -468,6 +544,16 @@ Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: |
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\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
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\& were used, return, otherwise continue with step *. |
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.Ve |
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.Sp |
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Example: queue some jobs and then loop until no events are outsanding |
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anymore. |
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.Sp |
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.Vb 4 |
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\& ... queue jobs here, make sure they register event watchers as long |
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\& ... as they still have work to do (even an idle watcher will do..) |
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\& ev_loop (my_loop, 0); |
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\& ... jobs done. yeah! |
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.Ve |
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.IP "ev_unloop (loop, how)" 4 |
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.IX Item "ev_unloop (loop, how)" |
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Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it |
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@ -490,6 +576,23 @@ visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exi |
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no event watchers registered by it are active. It is also an excellent |
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way to do this for generic recurring timers or from within third-party |
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libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. |
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.Sp |
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Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR |
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running when nothing else is active. |
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.Sp |
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.Vb 4 |
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\& struct dv_signal exitsig; |
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\& ev_signal_init (&exitsig, sig_cb, SIGINT); |
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\& ev_signal_start (myloop, &exitsig); |
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\& evf_unref (myloop); |
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.Ve |
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.Sp |
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Example: for some weird reason, unregister the above signal handler again. |
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.Sp |
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.Vb 2 |
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\& ev_ref (myloop); |
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\& ev_signal_stop (myloop, &exitsig); |
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.Ve |
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.SH "ANATOMY OF A WATCHER" |
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.IX Header "ANATOMY OF A WATCHER" |
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A watcher is a structure that you create and register to record your |
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@ -687,6 +790,28 @@ problem. Also note that it is quite easy to have your callback invoked |
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when the readyness condition is no longer valid even when employing |
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typical ways of handling events, so its a good idea to use non-blocking |
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I/O unconditionally. |
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.PP |
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Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well |
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readable, but only once. Since it is likely line\-buffered, you could |
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attempt to read a whole line in the callback: |
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.PP |
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.Vb 6 |
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\& static void |
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\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
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\& { |
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\& ev_io_stop (loop, w); |
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\& .. read from stdin here (or from w->fd) and haqndle any I/O errors |
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\& } |
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.Ve |
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.PP |
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.Vb 6 |
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\& ... |
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\& struct ev_loop *loop = ev_default_init (0); |
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\& struct ev_io stdin_readable; |
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\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); |
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\& ev_io_start (loop, &stdin_readable); |
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\& ev_loop (loop, 0); |
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.Ve |
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.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" |
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.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" |
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.IX Subsection "ev_timer - relative and optionally recurring timeouts" |
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@ -746,6 +871,46 @@ configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_time |
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time you successfully read or write some data. If you go into an idle |
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state where you do not expect data to travel on the socket, you can stop |
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the timer, and again will automatically restart it if need be. |
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.PP |
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Example: create a timer that fires after 60 seconds. |
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.PP |
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.Vb 5 |
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\& static void |
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\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
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\& { |
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\& .. one minute over, w is actually stopped right here |
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\& } |
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.Ve |
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.PP |
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.Vb 3 |
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\& struct ev_timer mytimer; |
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\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); |
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\& ev_timer_start (loop, &mytimer); |
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.Ve |
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.PP |
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Example: create a timeout timer that times out after 10 seconds of |
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inactivity. |
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.PP |
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.Vb 5 |
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\& static void |
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\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
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\& { |
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\& .. ten seconds without any activity |
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\& } |
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.Ve |
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.PP |
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.Vb 4 |
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\& struct ev_timer mytimer; |
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\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ |
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\& ev_timer_again (&mytimer); /* start timer */ |
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\& ev_loop (loop, 0); |
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.Ve |
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.PP |
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.Vb 3 |
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\& // and in some piece of code that gets executed on any "activity": |
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\& // reset the timeout to start ticking again at 10 seconds |
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\& ev_timer_again (&mytimer); |
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.Ve |
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.ie n .Sh """ev_periodic"" \- to cron or not to cron" |
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.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" |
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.IX Subsection "ev_periodic - to cron or not to cron" |
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@ -847,6 +1012,51 @@ Simply stops and restarts the periodic watcher again. This is only useful |
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when you changed some parameters or the reschedule callback would return |
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a different time than the last time it was called (e.g. in a crond like |
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program when the crontabs have changed). |
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.PP |
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Example: call a callback every hour, or, more precisely, whenever the |
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system clock is divisible by 3600. The callback invocation times have |
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potentially a lot of jittering, but good long-term stability. |
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.PP |
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.Vb 5 |
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\& static void |
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\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
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\& { |
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\& ... its now a full hour (UTC, or TAI or whatever your clock follows) |
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\& } |
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.Ve |
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.PP |
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.Vb 3 |
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\& struct ev_periodic hourly_tick; |
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\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); |
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\& ev_periodic_start (loop, &hourly_tick); |
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.Ve |
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.PP |
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Example: the same as above, but use a reschedule callback to do it: |
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.PP |
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.Vb 1 |
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\& #include <math.h> |
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.Ve |
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.PP |
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.Vb 5 |
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\& static ev_tstamp |
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\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) |
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\& { |
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\& return fmod (now, 3600.) + 3600.; |
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\& } |
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.Ve |
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.PP |
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.Vb 1 |
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\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); |
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.Ve |
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.PP |
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Example: call a callback every hour, starting now: |
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.PP |
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.Vb 4 |
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\& struct ev_periodic hourly_tick; |
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\& ev_periodic_init (&hourly_tick, clock_cb, |
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\& fmod (ev_now (loop), 3600.), 3600., 0); |
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\& ev_periodic_start (loop, &hourly_tick); |
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.Ve |
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.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" |
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.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" |
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.IX Subsection "ev_signal - signal me when a signal gets signalled" |
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@ -886,6 +1096,22 @@ at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watche |
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the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems |
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\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the |
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process causing the status change. |
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.PP |
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Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. |
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.PP |
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.Vb 5 |
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\& static void |
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\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) |
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\& { |
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\& ev_unloop (loop, EVUNLOOP_ALL); |
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\& } |
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.Ve |
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.PP |
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.Vb 3 |
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\& struct ev_signal signal_watcher; |
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\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); |
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\& ev_signal_start (loop, &sigint_cb); |
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.Ve |
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.ie n .Sh """ev_idle"" \- when you've got nothing better to do" |
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.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" |
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.IX Subsection "ev_idle - when you've got nothing better to do" |
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@ -909,6 +1135,25 @@ event loop has handled all outstanding events. |
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Initialises and configures the idle watcher \- it has no parameters of any |
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kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, |
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believe me. |
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.PP |
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Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the |
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callback, free it. Alos, use no error checking, as usual. |
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.PP |
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.Vb 7 |
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\& static void |
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\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) |
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\& { |
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\& free (w); |
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\& // now do something you wanted to do when the program has |
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\& // no longer asnything immediate to do. |
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\& } |
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.Ve |
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.PP |
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.Vb 3 |
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\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); |
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\& ev_idle_init (idle_watcher, idle_cb); |
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\& ev_idle_start (loop, idle_cb); |
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.Ve |
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.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" |
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.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" |
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.IX Subsection "ev_prepare and ev_check - customise your event loop" |
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@ -946,6 +1191,8 @@ low-priority coroutines to idle/background tasks). |
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Initialises and configures the prepare or check watcher \- they have no |
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parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR |
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macros, but using them is utterly, utterly and completely pointless. |
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.PP |
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Example: *TODO*. |
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.SH "OTHER FUNCTIONS" |
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.IX Header "OTHER FUNCTIONS" |
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There are some other functions of possible interest. Described. Here. Now. |
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Marc Alexander Lehmann
15 years ago