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=head1 NAME |
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libev - a high performance full-featured event loop written in C |
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=head1 SYNOPSIS |
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#include <ev.h> |
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=head1 DESCRIPTION |
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Libev is an event loop: you register interest in certain events (such as a |
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file descriptor being readable or a timeout occuring), and it will manage |
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these event sources and provide your program with events. |
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To do this, it must take more or less complete control over your process |
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(or thread) by executing the I<event loop> handler, and will then |
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communicate events via a callback mechanism. |
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You register interest in certain events by registering so-called I<event |
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watchers>, which are relatively small C structures you initialise with the |
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details of the event, and then hand it over to libev by I<starting> the |
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watcher. |
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=head1 FEATURES |
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Libev supports select, poll, the linux-specific epoll and the bsd-specific |
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kqueue mechanisms for file descriptor events, relative timers, absolute |
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timers with customised rescheduling, signal events, process status change |
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events (related to SIGCHLD), and event watchers dealing with the event |
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loop mechanism itself (idle, prepare and check watchers). It also is quite |
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fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing |
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it to libevent for example). |
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=head1 CONVENTIONS |
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Libev is very configurable. In this manual the default configuration |
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will be described, which supports multiple event loops. For more info |
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about various configuration options please have a look at the file |
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F<README.embed> in the libev distribution. If libev was configured without |
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support for multiple event loops, then all functions taking an initial |
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argument of name C<loop> (which is always of type C<struct ev_loop *>) |
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will not have this argument. |
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=head1 TIME REPRESENTATION |
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Libev represents time as a single floating point number, representing the |
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(fractional) number of seconds since the (POSIX) 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 C<ev_tstamp>, which is what you should use too. It usually aliases |
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to the double type in C. |
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=head1 GLOBAL FUNCTIONS |
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These functions can be called anytime, even before initialising the |
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library in any way. |
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=over 4 |
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=item ev_tstamp ev_time () |
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Returns the current time as libev would use it. Please note that the |
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C<ev_now> function is usually faster and also often returns the timestamp |
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you actually want to know. |
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=item int ev_version_major () |
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=item int ev_version_minor () |
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You can find out the major and minor version numbers of the library |
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you linked against by calling the functions C<ev_version_major> and |
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C<ev_version_minor>. If you want, you can compare against the global |
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symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the |
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version of the library your program was compiled against. |
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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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=item unsigned int ev_supported_backends () |
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Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*> |
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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 C<ev_default_loop> for |
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a description of the set values. |
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=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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recommended for this platform. This set is often smaller than the one |
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returned by C<ev_supported_backends>, as for example kqueue is broken on |
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most BSDs and will not be autodetected unless you explicitly request it |
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(assuming you know what you are doing). This is the set of backends that |
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C<EVFLAG_AUTO> will probe for. |
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=item ev_set_allocator (void *(*cb)(void *ptr, long size)) |
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Sets the allocation function to use (the prototype is similar to the |
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realloc C function, the semantics are identical). It is used to allocate |
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and free memory (no surprises here). If it returns zero when memory |
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needs to be allocated, the library might abort or take some potentially |
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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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=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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as failed select, poll, epoll_wait). The message is a printable string |
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indicating the system call or subsystem causing the problem. If this |
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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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=back |
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=head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
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An event loop is described by a C<struct ev_loop *>. The library knows two |
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types of such loops, the I<default> loop, which supports signals and child |
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events, and dynamically created loops which do not. |
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If you use threads, a common model is to run the default event loop |
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in your main thread (or in a separate thread) and for each thread you |
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create, you also create another event loop. Libev itself does no locking |
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whatsoever, so if you mix calls to the same event loop in different |
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threads, make sure you lock (this is usually a bad idea, though, even if |
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done correctly, because it's hideous and inefficient). |
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=over 4 |
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=item struct ev_loop *ev_default_loop (unsigned int flags) |
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This will initialise the default event loop if it hasn't been initialised |
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yet and return it. If the default loop could not be initialised, returns |
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false. If it already was initialised it simply returns it (and ignores the |
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flags. If that is troubling you, check C<ev_backend ()> afterwards). |
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If you don't know what event loop to use, use the one returned from this |
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function. |
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The flags argument can be used to specify special behaviour or specific |
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backends to use, and is usually specified as C<0> (or EVFLAG_AUTO). |
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It supports the following flags: |
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=over 4 |
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=item C<EVFLAG_AUTO> |
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The default flags value. Use this if you have no clue (it's the right |
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thing, believe me). |
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=item C<EVFLAG_NOENV> |
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If this flag bit is ored into the flag value (or the program runs setuid |
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or setgid) then libev will I<not> look at the environment variable |
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C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will |
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override the flags completely if it is found in the environment. This is |
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useful to try out specific backends to test their performance, or to work |
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around bugs. |
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=item C<EVBACKEND_SELECT> (value 1, portable select backend) |
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This is your standard select(2) backend. Not I<completely> standard, as |
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libev tries to roll its own fd_set with no limits on the number of fds, |
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but if that fails, expect a fairly low limit on the number of fds when |
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using this backend. It doesn't scale too well (O(highest_fd)), but its usually |
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the fastest backend for a low number of fds. |
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=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows) |
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And this is your standard poll(2) backend. It's more complicated than |
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select, but handles sparse fds better and has no artificial limit on the |
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number of fds you can use (except it will slow down considerably with a |
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lot of inactive fds). It scales similarly to select, i.e. O(total_fds). |
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=item C<EVBACKEND_EPOLL> (value 4, Linux) |
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For few fds, this backend is a bit little slower than poll and select, |
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but it scales phenomenally better. While poll and select usually scale like |
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O(total_fds) where n is the total number of fds (or the highest fd), epoll scales |
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either O(1) or O(active_fds). |
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While stopping and starting an I/O watcher in the same iteration will |
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result in some caching, there is still a syscall per such incident |
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(because the fd could point to a different file description now), so its |
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best to avoid that. Also, dup()ed file descriptors might not work very |
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well if you register events for both fds. |
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=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
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Kqueue deserves special mention, as at the time of this writing, it |
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was broken on all BSDs except NetBSD (usually it doesn't work with |
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anything but sockets and pipes, except on Darwin, where of course its |
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completely useless). For this reason its not being "autodetected" unless |
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you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO). |
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It scales in the same way as the epoll backend, but the interface to the |
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kernel is more efficient (which says nothing about its actual speed, of |
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course). While starting and stopping an I/O watcher does not cause an |
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extra syscall as with epoll, it still adds up to four event changes per |
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incident, so its best to avoid that. |
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=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8) |
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This is not implemented yet (and might never be). |
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=item C<EVBACKEND_PORT> (value 32, Solaris 10) |
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This uses the Solaris 10 port mechanism. As with everything on Solaris, |
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it's really slow, but it still scales very well (O(active_fds)). |
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=item C<EVBACKEND_ALL> |
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Try all backends (even potentially broken ones that wouldn't be tried |
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with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as |
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C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
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=back |
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If one or more of these are ored into the flags value, then only these |
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backends will be tried (in the reverse order as given here). If none are |
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specified, most compiled-in backend will be tried, usually in reverse |
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order of their flag values :) |
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=item struct ev_loop *ev_loop_new (unsigned int flags) |
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Similar to C<ev_default_loop>, but always creates a new event loop that is |
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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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=item ev_default_destroy () |
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Destroys the default loop again (frees all memory and kernel state |
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etc.). This stops all registered event watchers (by not touching them in |
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any way whatsoever, although you cannot rely on this :). |
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=item ev_loop_destroy (loop) |
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Like C<ev_default_destroy>, but destroys an event loop created by an |
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earlier call to C<ev_loop_new>. |
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=item ev_default_fork () |
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This function reinitialises the kernel state for backends that have |
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one. Despite the name, you can call it anytime, but it makes most sense |
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after forking, in either the parent or child process (or both, but that |
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again makes little sense). |
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You I<must> call this function in the child process after forking if and |
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only if you want to use the event library in both processes. If you just |
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fork+exec, you don't have to call it. |
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The function itself is quite fast and it's usually not a problem to call |
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it just in case after a fork. To make this easy, the function will fit in |
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quite nicely into a call to C<pthread_atfork>: |
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pthread_atfork (0, 0, ev_default_fork); |
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At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use |
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without calling this function, so if you force one of those backends you |
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do not need to care. |
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=item ev_loop_fork (loop) |
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Like C<ev_default_fork>, but acts on an event loop created by |
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C<ev_loop_new>. Yes, you have to call this on every allocated event loop |
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after fork, and how you do this is entirely your own problem. |
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=item unsigned int ev_backend (loop) |
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Returns one of the C<EVBACKEND_*> flags indicating the event backend in |
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use. |
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=item ev_tstamp ev_now (loop) |
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Returns the current "event loop time", 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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=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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after you initialised all your watchers and you want to start handling |
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events. |
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If the flags argument is specified as 0, it will not return until either |
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no event watchers are active anymore or C<ev_unloop> was called. |
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A flags value of C<EVLOOP_NONBLOCK> 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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A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
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neccessary) and will handle those and any outstanding ones. It will block |
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your process until at least one new event arrives, and will return after |
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one iteration of the loop. |
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This flags value could be used to implement alternative looping |
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constructs, but the C<prepare> and C<check> watchers provide a better and |
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more generic mechanism. |
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Here are the gory details of what ev_loop does: |
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1. If there are no active watchers (reference count is zero), return. |
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2. Queue and immediately call all prepare watchers. |
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3. If we have been forked, recreate the kernel state. |
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4. Update the kernel state with all outstanding changes. |
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5. Update the "event loop time". |
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6. Calculate for how long to block. |
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7. Block the process, waiting for events. |
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8. Update the "event loop time" and do time jump handling. |
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9. Queue all outstanding timers. |
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10. Queue all outstanding periodics. |
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11. If no events are pending now, queue all idle watchers. |
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12. Queue all check watchers. |
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13. Call all queued watchers in reverse order (i.e. check watchers first). |
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14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
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was used, return, otherwise continue with step #1. |
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=item ev_unloop (loop, how) |
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1.9 |
Can be used to make a call to C<ev_loop> return early (but only after it |
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has processed all outstanding events). The C<how> argument must be either |
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1.25 |
C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or |
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C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. |
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=item ev_ref (loop) |
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=item ev_unref (loop) |
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1.9 |
Ref/unref can be used to add or remove a reference count on the event |
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loop: Every watcher keeps one reference, and as long as the reference |
341 |
|
|
count is nonzero, C<ev_loop> will not return on its own. If you have |
342 |
|
|
a watcher you never unregister that should not keep C<ev_loop> from |
343 |
|
|
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
344 |
|
|
example, libev itself uses this for its internal signal pipe: It is not |
345 |
|
|
visible to the libev user and should not keep C<ev_loop> from exiting if |
346 |
|
|
no event watchers registered by it are active. It is also an excellent |
347 |
|
|
way to do this for generic recurring timers or from within third-party |
348 |
|
|
libraries. Just remember to I<unref after start> and I<ref before stop>. |
349 |
root |
1.1 |
|
350 |
|
|
=back |
351 |
|
|
|
352 |
|
|
=head1 ANATOMY OF A WATCHER |
353 |
|
|
|
354 |
|
|
A watcher is a structure that you create and register to record your |
355 |
|
|
interest in some event. For instance, if you want to wait for STDIN to |
356 |
root |
1.10 |
become readable, you would create an C<ev_io> watcher for that: |
357 |
root |
1.1 |
|
358 |
|
|
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
359 |
|
|
{ |
360 |
|
|
ev_io_stop (w); |
361 |
|
|
ev_unloop (loop, EVUNLOOP_ALL); |
362 |
|
|
} |
363 |
|
|
|
364 |
|
|
struct ev_loop *loop = ev_default_loop (0); |
365 |
|
|
struct ev_io stdin_watcher; |
366 |
|
|
ev_init (&stdin_watcher, my_cb); |
367 |
|
|
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
368 |
|
|
ev_io_start (loop, &stdin_watcher); |
369 |
|
|
ev_loop (loop, 0); |
370 |
|
|
|
371 |
|
|
As you can see, you are responsible for allocating the memory for your |
372 |
|
|
watcher structures (and it is usually a bad idea to do this on the stack, |
373 |
|
|
although this can sometimes be quite valid). |
374 |
|
|
|
375 |
|
|
Each watcher structure must be initialised by a call to C<ev_init |
376 |
|
|
(watcher *, callback)>, which expects a callback to be provided. This |
377 |
|
|
callback gets invoked each time the event occurs (or, in the case of io |
378 |
|
|
watchers, each time the event loop detects that the file descriptor given |
379 |
|
|
is readable and/or writable). |
380 |
|
|
|
381 |
|
|
Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
382 |
|
|
with arguments specific to this watcher type. There is also a macro |
383 |
|
|
to combine initialisation and setting in one call: C<< ev_<type>_init |
384 |
|
|
(watcher *, callback, ...) >>. |
385 |
|
|
|
386 |
|
|
To make the watcher actually watch out for events, you have to start it |
387 |
|
|
with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
388 |
|
|
*) >>), and you can stop watching for events at any time by calling the |
389 |
|
|
corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
390 |
|
|
|
391 |
|
|
As long as your watcher is active (has been started but not stopped) you |
392 |
|
|
must not touch the values stored in it. Most specifically you must never |
393 |
root |
1.31 |
reinitialise it or call its set macro. |
394 |
root |
1.1 |
|
395 |
root |
1.14 |
You can check whether an event is active by calling the C<ev_is_active |
396 |
root |
1.4 |
(watcher *)> macro. To see whether an event is outstanding (but the |
397 |
root |
1.14 |
callback for it has not been called yet) you can use the C<ev_is_pending |
398 |
root |
1.1 |
(watcher *)> macro. |
399 |
|
|
|
400 |
|
|
Each and every callback receives the event loop pointer as first, the |
401 |
|
|
registered watcher structure as second, and a bitset of received events as |
402 |
|
|
third argument. |
403 |
|
|
|
404 |
root |
1.14 |
The received events usually include a single bit per event type received |
405 |
root |
1.1 |
(you can receive multiple events at the same time). The possible bit masks |
406 |
|
|
are: |
407 |
|
|
|
408 |
|
|
=over 4 |
409 |
|
|
|
410 |
root |
1.10 |
=item C<EV_READ> |
411 |
root |
1.1 |
|
412 |
root |
1.10 |
=item C<EV_WRITE> |
413 |
root |
1.1 |
|
414 |
root |
1.10 |
The file descriptor in the C<ev_io> watcher has become readable and/or |
415 |
root |
1.1 |
writable. |
416 |
|
|
|
417 |
root |
1.10 |
=item C<EV_TIMEOUT> |
418 |
root |
1.1 |
|
419 |
root |
1.10 |
The C<ev_timer> watcher has timed out. |
420 |
root |
1.1 |
|
421 |
root |
1.10 |
=item C<EV_PERIODIC> |
422 |
root |
1.1 |
|
423 |
root |
1.10 |
The C<ev_periodic> watcher has timed out. |
424 |
root |
1.1 |
|
425 |
root |
1.10 |
=item C<EV_SIGNAL> |
426 |
root |
1.1 |
|
427 |
root |
1.10 |
The signal specified in the C<ev_signal> watcher has been received by a thread. |
428 |
root |
1.1 |
|
429 |
root |
1.10 |
=item C<EV_CHILD> |
430 |
root |
1.1 |
|
431 |
root |
1.10 |
The pid specified in the C<ev_child> watcher has received a status change. |
432 |
root |
1.1 |
|
433 |
root |
1.10 |
=item C<EV_IDLE> |
434 |
root |
1.1 |
|
435 |
root |
1.10 |
The C<ev_idle> watcher has determined that you have nothing better to do. |
436 |
root |
1.1 |
|
437 |
root |
1.10 |
=item C<EV_PREPARE> |
438 |
root |
1.1 |
|
439 |
root |
1.10 |
=item C<EV_CHECK> |
440 |
root |
1.1 |
|
441 |
root |
1.10 |
All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts |
442 |
|
|
to gather new events, and all C<ev_check> watchers are invoked just after |
443 |
root |
1.1 |
C<ev_loop> has gathered them, but before it invokes any callbacks for any |
444 |
|
|
received events. Callbacks of both watcher types can start and stop as |
445 |
|
|
many watchers as they want, and all of them will be taken into account |
446 |
root |
1.10 |
(for example, a C<ev_prepare> watcher might start an idle watcher to keep |
447 |
root |
1.1 |
C<ev_loop> from blocking). |
448 |
|
|
|
449 |
root |
1.10 |
=item C<EV_ERROR> |
450 |
root |
1.1 |
|
451 |
|
|
An unspecified error has occured, the watcher has been stopped. This might |
452 |
|
|
happen because the watcher could not be properly started because libev |
453 |
|
|
ran out of memory, a file descriptor was found to be closed or any other |
454 |
|
|
problem. You best act on it by reporting the problem and somehow coping |
455 |
|
|
with the watcher being stopped. |
456 |
|
|
|
457 |
|
|
Libev will usually signal a few "dummy" events together with an error, |
458 |
|
|
for example it might indicate that a fd is readable or writable, and if |
459 |
|
|
your callbacks is well-written it can just attempt the operation and cope |
460 |
|
|
with the error from read() or write(). This will not work in multithreaded |
461 |
|
|
programs, though, so beware. |
462 |
|
|
|
463 |
|
|
=back |
464 |
|
|
|
465 |
|
|
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
466 |
|
|
|
467 |
|
|
Each watcher has, by default, a member C<void *data> that you can change |
468 |
root |
1.14 |
and read at any time, libev will completely ignore it. This can be used |
469 |
root |
1.1 |
to associate arbitrary data with your watcher. If you need more data and |
470 |
|
|
don't want to allocate memory and store a pointer to it in that data |
471 |
|
|
member, you can also "subclass" the watcher type and provide your own |
472 |
|
|
data: |
473 |
|
|
|
474 |
|
|
struct my_io |
475 |
|
|
{ |
476 |
|
|
struct ev_io io; |
477 |
|
|
int otherfd; |
478 |
|
|
void *somedata; |
479 |
|
|
struct whatever *mostinteresting; |
480 |
|
|
} |
481 |
|
|
|
482 |
|
|
And since your callback will be called with a pointer to the watcher, you |
483 |
|
|
can cast it back to your own type: |
484 |
|
|
|
485 |
|
|
static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
486 |
|
|
{ |
487 |
|
|
struct my_io *w = (struct my_io *)w_; |
488 |
|
|
... |
489 |
|
|
} |
490 |
|
|
|
491 |
|
|
More interesting and less C-conformant ways of catsing your callback type |
492 |
|
|
have been omitted.... |
493 |
|
|
|
494 |
|
|
|
495 |
|
|
=head1 WATCHER TYPES |
496 |
|
|
|
497 |
|
|
This section describes each watcher in detail, but will not repeat |
498 |
|
|
information given in the last section. |
499 |
|
|
|
500 |
root |
1.11 |
=head2 C<ev_io> - is this file descriptor readable or writable |
501 |
root |
1.1 |
|
502 |
root |
1.4 |
I/O watchers check whether a file descriptor is readable or writable |
503 |
root |
1.1 |
in each iteration of the event loop (This behaviour is called |
504 |
|
|
level-triggering because you keep receiving events as long as the |
505 |
root |
1.14 |
condition persists. Remember you can stop the watcher if you don't want to |
506 |
root |
1.1 |
act on the event and neither want to receive future events). |
507 |
|
|
|
508 |
root |
1.23 |
In general you can register as many read and/or write event watchers per |
509 |
root |
1.8 |
fd as you want (as long as you don't confuse yourself). Setting all file |
510 |
|
|
descriptors to non-blocking mode is also usually a good idea (but not |
511 |
|
|
required if you know what you are doing). |
512 |
|
|
|
513 |
|
|
You have to be careful with dup'ed file descriptors, though. Some backends |
514 |
|
|
(the linux epoll backend is a notable example) cannot handle dup'ed file |
515 |
|
|
descriptors correctly if you register interest in two or more fds pointing |
516 |
root |
1.24 |
to the same underlying file/socket etc. description (that is, they share |
517 |
|
|
the same underlying "file open"). |
518 |
root |
1.8 |
|
519 |
|
|
If you must do this, then force the use of a known-to-be-good backend |
520 |
root |
1.31 |
(at the time of this writing, this includes only C<EVBACKEND_SELECT> and |
521 |
|
|
C<EVBACKEND_POLL>). |
522 |
root |
1.8 |
|
523 |
root |
1.1 |
=over 4 |
524 |
|
|
|
525 |
|
|
=item ev_io_init (ev_io *, callback, int fd, int events) |
526 |
|
|
|
527 |
|
|
=item ev_io_set (ev_io *, int fd, int events) |
528 |
|
|
|
529 |
root |
1.10 |
Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive |
530 |
root |
1.1 |
events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | |
531 |
|
|
EV_WRITE> to receive the given events. |
532 |
|
|
|
533 |
|
|
=back |
534 |
|
|
|
535 |
root |
1.10 |
=head2 C<ev_timer> - relative and optionally recurring timeouts |
536 |
root |
1.1 |
|
537 |
|
|
Timer watchers are simple relative timers that generate an event after a |
538 |
|
|
given time, and optionally repeating in regular intervals after that. |
539 |
|
|
|
540 |
|
|
The timers are based on real time, that is, if you register an event that |
541 |
root |
1.22 |
times out after an hour and you reset your system clock to last years |
542 |
root |
1.1 |
time, it will still time out after (roughly) and hour. "Roughly" because |
543 |
root |
1.28 |
detecting time jumps is hard, and some inaccuracies are unavoidable (the |
544 |
root |
1.1 |
monotonic clock option helps a lot here). |
545 |
|
|
|
546 |
root |
1.9 |
The relative timeouts are calculated relative to the C<ev_now ()> |
547 |
|
|
time. This is usually the right thing as this timestamp refers to the time |
548 |
root |
1.28 |
of the event triggering whatever timeout you are modifying/starting. If |
549 |
|
|
you suspect event processing to be delayed and you I<need> to base the timeout |
550 |
root |
1.22 |
on the current time, use something like this to adjust for this: |
551 |
root |
1.9 |
|
552 |
|
|
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
553 |
|
|
|
554 |
root |
1.28 |
The callback is guarenteed to be invoked only when its timeout has passed, |
555 |
|
|
but if multiple timers become ready during the same loop iteration then |
556 |
|
|
order of execution is undefined. |
557 |
|
|
|
558 |
root |
1.1 |
=over 4 |
559 |
|
|
|
560 |
|
|
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) |
561 |
|
|
|
562 |
|
|
=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) |
563 |
|
|
|
564 |
|
|
Configure the timer to trigger after C<after> seconds. If C<repeat> is |
565 |
|
|
C<0.>, then it will automatically be stopped. If it is positive, then the |
566 |
|
|
timer will automatically be configured to trigger again C<repeat> seconds |
567 |
|
|
later, again, and again, until stopped manually. |
568 |
|
|
|
569 |
|
|
The timer itself will do a best-effort at avoiding drift, that is, if you |
570 |
|
|
configure a timer to trigger every 10 seconds, then it will trigger at |
571 |
|
|
exactly 10 second intervals. If, however, your program cannot keep up with |
572 |
root |
1.22 |
the timer (because it takes longer than those 10 seconds to do stuff) the |
573 |
root |
1.1 |
timer will not fire more than once per event loop iteration. |
574 |
|
|
|
575 |
|
|
=item ev_timer_again (loop) |
576 |
|
|
|
577 |
|
|
This will act as if the timer timed out and restart it again if it is |
578 |
|
|
repeating. The exact semantics are: |
579 |
|
|
|
580 |
|
|
If the timer is started but nonrepeating, stop it. |
581 |
|
|
|
582 |
|
|
If the timer is repeating, either start it if necessary (with the repeat |
583 |
|
|
value), or reset the running timer to the repeat value. |
584 |
|
|
|
585 |
|
|
This sounds a bit complicated, but here is a useful and typical |
586 |
|
|
example: Imagine you have a tcp connection and you want a so-called idle |
587 |
|
|
timeout, that is, you want to be called when there have been, say, 60 |
588 |
|
|
seconds of inactivity on the socket. The easiest way to do this is to |
589 |
root |
1.10 |
configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each |
590 |
root |
1.1 |
time you successfully read or write some data. If you go into an idle |
591 |
|
|
state where you do not expect data to travel on the socket, you can stop |
592 |
|
|
the timer, and again will automatically restart it if need be. |
593 |
|
|
|
594 |
|
|
=back |
595 |
|
|
|
596 |
root |
1.14 |
=head2 C<ev_periodic> - to cron or not to cron |
597 |
root |
1.1 |
|
598 |
|
|
Periodic watchers are also timers of a kind, but they are very versatile |
599 |
|
|
(and unfortunately a bit complex). |
600 |
|
|
|
601 |
root |
1.10 |
Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
602 |
root |
1.1 |
but on wallclock time (absolute time). You can tell a periodic watcher |
603 |
|
|
to trigger "at" some specific point in time. For example, if you tell a |
604 |
|
|
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
605 |
|
|
+ 10.>) and then reset your system clock to the last year, then it will |
606 |
root |
1.10 |
take a year to trigger the event (unlike an C<ev_timer>, which would trigger |
607 |
root |
1.1 |
roughly 10 seconds later and of course not if you reset your system time |
608 |
|
|
again). |
609 |
|
|
|
610 |
|
|
They can also be used to implement vastly more complex timers, such as |
611 |
|
|
triggering an event on eahc midnight, local time. |
612 |
|
|
|
613 |
root |
1.28 |
As with timers, the callback is guarenteed to be invoked only when the |
614 |
|
|
time (C<at>) has been passed, but if multiple periodic timers become ready |
615 |
|
|
during the same loop iteration then order of execution is undefined. |
616 |
|
|
|
617 |
root |
1.1 |
=over 4 |
618 |
|
|
|
619 |
|
|
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
620 |
|
|
|
621 |
|
|
=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
622 |
|
|
|
623 |
|
|
Lots of arguments, lets sort it out... There are basically three modes of |
624 |
|
|
operation, and we will explain them from simplest to complex: |
625 |
|
|
|
626 |
|
|
=over 4 |
627 |
|
|
|
628 |
|
|
=item * absolute timer (interval = reschedule_cb = 0) |
629 |
|
|
|
630 |
|
|
In this configuration the watcher triggers an event at the wallclock time |
631 |
|
|
C<at> and doesn't repeat. It will not adjust when a time jump occurs, |
632 |
|
|
that is, if it is to be run at January 1st 2011 then it will run when the |
633 |
|
|
system time reaches or surpasses this time. |
634 |
|
|
|
635 |
|
|
=item * non-repeating interval timer (interval > 0, reschedule_cb = 0) |
636 |
|
|
|
637 |
|
|
In this mode the watcher will always be scheduled to time out at the next |
638 |
|
|
C<at + N * interval> time (for some integer N) and then repeat, regardless |
639 |
|
|
of any time jumps. |
640 |
|
|
|
641 |
|
|
This can be used to create timers that do not drift with respect to system |
642 |
|
|
time: |
643 |
|
|
|
644 |
|
|
ev_periodic_set (&periodic, 0., 3600., 0); |
645 |
|
|
|
646 |
|
|
This doesn't mean there will always be 3600 seconds in between triggers, |
647 |
|
|
but only that the the callback will be called when the system time shows a |
648 |
root |
1.12 |
full hour (UTC), or more correctly, when the system time is evenly divisible |
649 |
root |
1.1 |
by 3600. |
650 |
|
|
|
651 |
|
|
Another way to think about it (for the mathematically inclined) is that |
652 |
root |
1.10 |
C<ev_periodic> will try to run the callback in this mode at the next possible |
653 |
root |
1.1 |
time where C<time = at (mod interval)>, regardless of any time jumps. |
654 |
|
|
|
655 |
|
|
=item * manual reschedule mode (reschedule_cb = callback) |
656 |
|
|
|
657 |
|
|
In this mode the values for C<interval> and C<at> are both being |
658 |
|
|
ignored. Instead, each time the periodic watcher gets scheduled, the |
659 |
|
|
reschedule callback will be called with the watcher as first, and the |
660 |
|
|
current time as second argument. |
661 |
|
|
|
662 |
root |
1.18 |
NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
663 |
|
|
ever, or make any event loop modifications>. If you need to stop it, |
664 |
|
|
return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by |
665 |
|
|
starting a prepare watcher). |
666 |
root |
1.1 |
|
667 |
root |
1.13 |
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
668 |
root |
1.1 |
ev_tstamp now)>, e.g.: |
669 |
|
|
|
670 |
|
|
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
671 |
|
|
{ |
672 |
|
|
return now + 60.; |
673 |
|
|
} |
674 |
|
|
|
675 |
|
|
It must return the next time to trigger, based on the passed time value |
676 |
|
|
(that is, the lowest time value larger than to the second argument). It |
677 |
|
|
will usually be called just before the callback will be triggered, but |
678 |
|
|
might be called at other times, too. |
679 |
|
|
|
680 |
root |
1.18 |
NOTE: I<< This callback must always return a time that is later than the |
681 |
root |
1.19 |
passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger. |
682 |
root |
1.18 |
|
683 |
root |
1.1 |
This can be used to create very complex timers, such as a timer that |
684 |
|
|
triggers on each midnight, local time. To do this, you would calculate the |
685 |
root |
1.19 |
next midnight after C<now> and return the timestamp value for this. How |
686 |
|
|
you do this is, again, up to you (but it is not trivial, which is the main |
687 |
|
|
reason I omitted it as an example). |
688 |
root |
1.1 |
|
689 |
|
|
=back |
690 |
|
|
|
691 |
|
|
=item ev_periodic_again (loop, ev_periodic *) |
692 |
|
|
|
693 |
|
|
Simply stops and restarts the periodic watcher again. This is only useful |
694 |
|
|
when you changed some parameters or the reschedule callback would return |
695 |
|
|
a different time than the last time it was called (e.g. in a crond like |
696 |
|
|
program when the crontabs have changed). |
697 |
|
|
|
698 |
|
|
=back |
699 |
|
|
|
700 |
root |
1.10 |
=head2 C<ev_signal> - signal me when a signal gets signalled |
701 |
root |
1.1 |
|
702 |
|
|
Signal watchers will trigger an event when the process receives a specific |
703 |
|
|
signal one or more times. Even though signals are very asynchronous, libev |
704 |
root |
1.9 |
will try it's best to deliver signals synchronously, i.e. as part of the |
705 |
root |
1.1 |
normal event processing, like any other event. |
706 |
|
|
|
707 |
root |
1.14 |
You can configure as many watchers as you like per signal. Only when the |
708 |
root |
1.1 |
first watcher gets started will libev actually register a signal watcher |
709 |
|
|
with the kernel (thus it coexists with your own signal handlers as long |
710 |
|
|
as you don't register any with libev). Similarly, when the last signal |
711 |
|
|
watcher for a signal is stopped libev will reset the signal handler to |
712 |
|
|
SIG_DFL (regardless of what it was set to before). |
713 |
|
|
|
714 |
|
|
=over 4 |
715 |
|
|
|
716 |
|
|
=item ev_signal_init (ev_signal *, callback, int signum) |
717 |
|
|
|
718 |
|
|
=item ev_signal_set (ev_signal *, int signum) |
719 |
|
|
|
720 |
|
|
Configures the watcher to trigger on the given signal number (usually one |
721 |
|
|
of the C<SIGxxx> constants). |
722 |
|
|
|
723 |
|
|
=back |
724 |
|
|
|
725 |
root |
1.10 |
=head2 C<ev_child> - wait for pid status changes |
726 |
root |
1.1 |
|
727 |
|
|
Child watchers trigger when your process receives a SIGCHLD in response to |
728 |
|
|
some child status changes (most typically when a child of yours dies). |
729 |
|
|
|
730 |
|
|
=over 4 |
731 |
|
|
|
732 |
|
|
=item ev_child_init (ev_child *, callback, int pid) |
733 |
|
|
|
734 |
|
|
=item ev_child_set (ev_child *, int pid) |
735 |
|
|
|
736 |
|
|
Configures the watcher to wait for status changes of process C<pid> (or |
737 |
|
|
I<any> process if C<pid> is specified as C<0>). The callback can look |
738 |
|
|
at the C<rstatus> member of the C<ev_child> watcher structure to see |
739 |
root |
1.14 |
the status word (use the macros from C<sys/wait.h> and see your systems |
740 |
|
|
C<waitpid> documentation). The C<rpid> member contains the pid of the |
741 |
|
|
process causing the status change. |
742 |
root |
1.1 |
|
743 |
|
|
=back |
744 |
|
|
|
745 |
root |
1.10 |
=head2 C<ev_idle> - when you've got nothing better to do |
746 |
root |
1.1 |
|
747 |
root |
1.14 |
Idle watchers trigger events when there are no other events are pending |
748 |
|
|
(prepare, check and other idle watchers do not count). That is, as long |
749 |
|
|
as your process is busy handling sockets or timeouts (or even signals, |
750 |
|
|
imagine) it will not be triggered. But when your process is idle all idle |
751 |
|
|
watchers are being called again and again, once per event loop iteration - |
752 |
|
|
until stopped, that is, or your process receives more events and becomes |
753 |
|
|
busy. |
754 |
root |
1.1 |
|
755 |
|
|
The most noteworthy effect is that as long as any idle watchers are |
756 |
|
|
active, the process will not block when waiting for new events. |
757 |
|
|
|
758 |
|
|
Apart from keeping your process non-blocking (which is a useful |
759 |
|
|
effect on its own sometimes), idle watchers are a good place to do |
760 |
|
|
"pseudo-background processing", or delay processing stuff to after the |
761 |
|
|
event loop has handled all outstanding events. |
762 |
|
|
|
763 |
|
|
=over 4 |
764 |
|
|
|
765 |
|
|
=item ev_idle_init (ev_signal *, callback) |
766 |
|
|
|
767 |
|
|
Initialises and configures the idle watcher - it has no parameters of any |
768 |
|
|
kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
769 |
|
|
believe me. |
770 |
|
|
|
771 |
|
|
=back |
772 |
|
|
|
773 |
root |
1.16 |
=head2 C<ev_prepare> and C<ev_check> - customise your event loop |
774 |
root |
1.1 |
|
775 |
root |
1.14 |
Prepare and check watchers are usually (but not always) used in tandem: |
776 |
root |
1.20 |
prepare watchers get invoked before the process blocks and check watchers |
777 |
root |
1.14 |
afterwards. |
778 |
root |
1.1 |
|
779 |
|
|
Their main purpose is to integrate other event mechanisms into libev. This |
780 |
|
|
could be used, for example, to track variable changes, implement your own |
781 |
|
|
watchers, integrate net-snmp or a coroutine library and lots more. |
782 |
|
|
|
783 |
|
|
This is done by examining in each prepare call which file descriptors need |
784 |
root |
1.14 |
to be watched by the other library, registering C<ev_io> watchers for |
785 |
|
|
them and starting an C<ev_timer> watcher for any timeouts (many libraries |
786 |
|
|
provide just this functionality). Then, in the check watcher you check for |
787 |
|
|
any events that occured (by checking the pending status of all watchers |
788 |
|
|
and stopping them) and call back into the library. The I/O and timer |
789 |
root |
1.20 |
callbacks will never actually be called (but must be valid nevertheless, |
790 |
root |
1.14 |
because you never know, you know?). |
791 |
root |
1.1 |
|
792 |
root |
1.14 |
As another example, the Perl Coro module uses these hooks to integrate |
793 |
root |
1.1 |
coroutines into libev programs, by yielding to other active coroutines |
794 |
|
|
during each prepare and only letting the process block if no coroutines |
795 |
root |
1.20 |
are ready to run (it's actually more complicated: it only runs coroutines |
796 |
|
|
with priority higher than or equal to the event loop and one coroutine |
797 |
|
|
of lower priority, but only once, using idle watchers to keep the event |
798 |
|
|
loop from blocking if lower-priority coroutines are active, thus mapping |
799 |
|
|
low-priority coroutines to idle/background tasks). |
800 |
root |
1.1 |
|
801 |
|
|
=over 4 |
802 |
|
|
|
803 |
|
|
=item ev_prepare_init (ev_prepare *, callback) |
804 |
|
|
|
805 |
|
|
=item ev_check_init (ev_check *, callback) |
806 |
|
|
|
807 |
|
|
Initialises and configures the prepare or check watcher - they have no |
808 |
|
|
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> |
809 |
root |
1.14 |
macros, but using them is utterly, utterly and completely pointless. |
810 |
root |
1.1 |
|
811 |
|
|
=back |
812 |
|
|
|
813 |
|
|
=head1 OTHER FUNCTIONS |
814 |
|
|
|
815 |
root |
1.14 |
There are some other functions of possible interest. Described. Here. Now. |
816 |
root |
1.1 |
|
817 |
|
|
=over 4 |
818 |
|
|
|
819 |
|
|
=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) |
820 |
|
|
|
821 |
|
|
This function combines a simple timer and an I/O watcher, calls your |
822 |
|
|
callback on whichever event happens first and automatically stop both |
823 |
|
|
watchers. This is useful if you want to wait for a single event on an fd |
824 |
root |
1.22 |
or timeout without having to allocate/configure/start/stop/free one or |
825 |
root |
1.1 |
more watchers yourself. |
826 |
|
|
|
827 |
root |
1.14 |
If C<fd> is less than 0, then no I/O watcher will be started and events |
828 |
|
|
is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and |
829 |
|
|
C<events> set will be craeted and started. |
830 |
root |
1.1 |
|
831 |
|
|
If C<timeout> is less than 0, then no timeout watcher will be |
832 |
root |
1.14 |
started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and |
833 |
|
|
repeat = 0) will be started. While C<0> is a valid timeout, it is of |
834 |
|
|
dubious value. |
835 |
|
|
|
836 |
|
|
The callback has the type C<void (*cb)(int revents, void *arg)> and gets |
837 |
root |
1.21 |
passed an C<revents> set like normal event callbacks (a combination of |
838 |
root |
1.14 |
C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> |
839 |
|
|
value passed to C<ev_once>: |
840 |
root |
1.1 |
|
841 |
|
|
static void stdin_ready (int revents, void *arg) |
842 |
|
|
{ |
843 |
|
|
if (revents & EV_TIMEOUT) |
844 |
root |
1.14 |
/* doh, nothing entered */; |
845 |
root |
1.1 |
else if (revents & EV_READ) |
846 |
root |
1.14 |
/* stdin might have data for us, joy! */; |
847 |
root |
1.1 |
} |
848 |
|
|
|
849 |
root |
1.14 |
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
850 |
root |
1.1 |
|
851 |
|
|
=item ev_feed_event (loop, watcher, int events) |
852 |
|
|
|
853 |
|
|
Feeds the given event set into the event loop, as if the specified event |
854 |
root |
1.14 |
had happened for the specified watcher (which must be a pointer to an |
855 |
|
|
initialised but not necessarily started event watcher). |
856 |
root |
1.1 |
|
857 |
|
|
=item ev_feed_fd_event (loop, int fd, int revents) |
858 |
|
|
|
859 |
root |
1.14 |
Feed an event on the given fd, as if a file descriptor backend detected |
860 |
|
|
the given events it. |
861 |
root |
1.1 |
|
862 |
|
|
=item ev_feed_signal_event (loop, int signum) |
863 |
|
|
|
864 |
|
|
Feed an event as if the given signal occured (loop must be the default loop!). |
865 |
|
|
|
866 |
|
|
=back |
867 |
|
|
|
868 |
root |
1.20 |
=head1 LIBEVENT EMULATION |
869 |
|
|
|
870 |
root |
1.24 |
Libev offers a compatibility emulation layer for libevent. It cannot |
871 |
|
|
emulate the internals of libevent, so here are some usage hints: |
872 |
|
|
|
873 |
|
|
=over 4 |
874 |
|
|
|
875 |
|
|
=item * Use it by including <event.h>, as usual. |
876 |
|
|
|
877 |
|
|
=item * The following members are fully supported: ev_base, ev_callback, |
878 |
|
|
ev_arg, ev_fd, ev_res, ev_events. |
879 |
|
|
|
880 |
|
|
=item * Avoid using ev_flags and the EVLIST_*-macros, while it is |
881 |
|
|
maintained by libev, it does not work exactly the same way as in libevent (consider |
882 |
|
|
it a private API). |
883 |
|
|
|
884 |
|
|
=item * Priorities are not currently supported. Initialising priorities |
885 |
|
|
will fail and all watchers will have the same priority, even though there |
886 |
|
|
is an ev_pri field. |
887 |
|
|
|
888 |
|
|
=item * Other members are not supported. |
889 |
|
|
|
890 |
|
|
=item * The libev emulation is I<not> ABI compatible to libevent, you need |
891 |
|
|
to use the libev header file and library. |
892 |
|
|
|
893 |
|
|
=back |
894 |
root |
1.20 |
|
895 |
|
|
=head1 C++ SUPPORT |
896 |
|
|
|
897 |
|
|
TBD. |
898 |
|
|
|
899 |
root |
1.1 |
=head1 AUTHOR |
900 |
|
|
|
901 |
|
|
Marc Lehmann <libev@schmorp.de>. |
902 |
|
|
|