[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.1 by root, Mon Nov 12 07:58:13 2007 UTC vs.
Revision 1.12 by root, Mon Nov 12 08:35:18 2007 UTC

 =head1 DESCRIPTION
 Libev is an event loop: you register interest in certain events (such as a
 file descriptor being readable or a timeout occuring), and it will manage
-these event sources and provide your program events.
+these event sources and provide your program with events.
 To do this, it must take more or less complete control over your process
 (or thread) by executing the I<event loop> handler, and will then
 communicate events via a callback mechanism.
 Libev supports select, poll, the linux-specific epoll and the bsd-specific
 kqueue mechanisms for file descriptor events, relative timers, absolute
 timers with customised rescheduling, signal events, process status change
 events (related to SIGCHLD), and event watchers dealing with the event
-loop mechanism itself (idle, prepare and check watchers).
+loop mechanism itself (idle, prepare and check watchers). It also is quite
+fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
+it to libevent for example).
 =head1 CONVENTIONS
 Libev is very configurable. In this manual the default configuration
 will be described, which supports multiple event loops. For more info
-about various configuraiton options please have a look at the file
+about various configuration options please have a look at the file
 F<README.embed> in the libev distribution. If libev was configured without
 support for multiple event loops, then all functions taking an initial
 argument of name C<loop> (which is always of type C<struct ev_loop *>)
 will not have this argument.
 =head1 TIME AND OTHER GLOBAL FUNCTIONS
-Libev represents time as a single floating point number. This type is
+Libev represents time as a single floating point number, representing the
+(fractional) number of seconds since the (POSIX) epoch (somewhere near
+the beginning of 1970, details are complicated, don't ask). This type is
 called C<ev_tstamp>, which is what you should use too. It usually aliases
 to the double type in C.
 =over 4
 you linked against by calling the functions C<ev_version_major> and
 C<ev_version_minor>. If you want, you can compare against the global
 symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
 version of the library your program was compiled against.
-Usually, its a good idea to terminate if the major versions mismatch,
+Usually, it's a good idea to terminate if the major versions mismatch,
 as this indicates an incompatible change.  Minor versions are usually
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 =item ev_set_allocator (void *(*cb)(void *ptr, long size))
 Sets the allocation function to use (the prototype is similar to the
-realloc function). It is used to allocate and free memory (no surprises
+realloc C function, the semantics are identical). It is used to allocate
-here). If it returns zero when memory needs to be allocated, the library
+and free memory (no surprises here). If it returns zero when memory
-might abort or take some potentially destructive action. The default is
+needs to be allocated, the library might abort or take some potentially
-your system realloc function.
+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.
 Set the callback function to call on a retryable syscall error (such
 as failed select, poll, epoll_wait). The message is a printable string
 indicating the system call or subsystem causing the problem. If this
 callback is set, then libev will expect it to remedy the sitution, no
-matter what, when it returns. That is, libev will geenrally retry the
+matter what, when it returns. That is, libev will generally retry the
 requested operation, or, if the condition doesn't go away, do bad stuff
 (such as abort).
 =back
 types of such loops, the I<default> loop, which supports signals and child
 events, and dynamically created loops which do not.
 If you use threads, a common model is to run the default event loop
 in your main thread (or in a separate thrad) and for each thread you
-create, you also create another event loop. Libev itself does no lockign
+create, you also create another event loop. Libev itself does no locking
-whatsoever, so if you mix calls to different event loops, make sure you
+whatsoever, so if you mix calls to the same event loop in different
-lock (this is usually a bad idea, though, even if done right).
+threads, make sure you lock (this is usually a bad idea, though, even if
+done correctly, because it's hideous and inefficient).
 =over 4
 =item struct ev_loop *ev_default_loop (unsigned int flags)
 If you don't know what event loop to use, use the one returned from this
 function.
 The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or EVFLAG_AUTO)
+backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
 It supports the following flags:
 =over 4
-=item EVFLAG_AUTO
+=item C<EVFLAG_AUTO>
-The default flags value. Use this if you have no clue (its the right
+The default flags value. Use this if you have no clue (it's the right
 thing, believe me).
-=item EVFLAG_NOENV
+=item C<EVFLAG_NOENV>
-If this flag bit is ored into the flag value then libev will I<not> look
+If this flag bit is ored into the flag value (or the program runs setuid
-at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this
+or setgid) then libev will I<not> look at the environment variable
-environment variable will override the flags completely. This is useful
+C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
+override the flags completely if it is found in the environment. This is
-to try out specific backends to tets their performance, or to work around
+useful to try out specific backends to test their performance, or to work
-bugs.
+around bugs.
-=item EVMETHOD_SELECT  portable select backend
+=item C<EVMETHOD_SELECT>  (portable select backend)
-=item EVMETHOD_POLL    poll backend (everywhere except windows)
+=item C<EVMETHOD_POLL>    (poll backend, available everywhere except on windows)
-=item EVMETHOD_EPOLL   linux only
+=item C<EVMETHOD_EPOLL>   (linux only)
-=item EVMETHOD_KQUEUE  some bsds only
+=item C<EVMETHOD_KQUEUE>  (some bsds only)
-=item EVMETHOD_DEVPOLL solaris 8 only
+=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
-=item EVMETHOD_PORT    solaris 10 only
+=item C<EVMETHOD_PORT>    (solaris 10 only)
 If one or more of these are ored into the flags value, then only these
 backends will be tried (in the reverse order as given here). If one are
 specified, any backend will do.
 =item ev_default_destroy ()
 Destroys the default loop again (frees all memory and kernel state
 etc.). This stops all registered event watchers (by not touching them in
-any way whatsoever, although you cnanot rely on this :).
+any way whatsoever, although you cannot rely on this :).
 =item ev_loop_destroy (loop)
 Like C<ev_default_destroy>, but destroys an event loop created by an
 earlier call to C<ev_loop_new>.
 You I<must> call this function after forking if and only if you want to
 use the event library in both processes. If you just fork+exec, you don't
 have to call it.
-The function itself is quite fast and its usually not a problem to call
+The function itself is quite fast and it's usually not a problem to call
 it just in case after a fork. To make this easy, the function will fit in
 quite nicely into a call to C<pthread_atfork>:
     pthread_atfork (0, 0, ev_default_fork);
 =item unsigned int ev_method (loop)
 Returns one of the C<EVMETHOD_*> flags indicating the event backend in
 use.
-=item ev_tstamp = ev_now (loop)
+=item ev_tstamp ev_now (loop)
 Returns the current "event loop time", which is the time the event loop
 got events and started processing them. This timestamp does not change
 as long as callbacks are being processed, and this is also the base time
 used for relative timers. You can treat it as the timestamp of the event
 If the flags argument is specified as 0, it will not return until either
 no event watchers are active anymore or C<ev_unloop> was called.
 A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
 those events and any outstanding ones, but will not block your process in
-case there are no events.
+case there are no events and will return after one iteration of the loop.
 A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
 neccessary) and will handle those and any outstanding ones. It will block
-your process until at least one new event arrives.
+your process until at least one new event arrives, and will return after
+one iteration of the loop.
 This flags value could be used to implement alternative looping
 constructs, but the C<prepare> and C<check> watchers provide a better and
 more generic mechanism.
 =item ev_unloop (loop, how)
-Can be used to make a call to C<ev_loop> return early. The C<how> argument
+Can be used to make a call to C<ev_loop> return early (but only after it
+has processed all outstanding events). The C<how> argument must be either
-must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>
+C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
-call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>
+C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
-calls return.
 =item ev_ref (loop)
 =item ev_unref (loop)
-Ref/unref can be used to add or remove a refcount on the event loop: Every
+Ref/unref can be used to add or remove a reference count on the event
-watcher keeps one reference. If you have a long-runing watcher you never
+loop: Every watcher keeps one reference, and as long as the reference
-unregister that should not keep ev_loop from running, ev_unref() after
+count is nonzero, C<ev_loop> will not return on its own. If you have
-starting, and ev_ref() before stopping it. Libev itself uses this for
+a watcher you never unregister that should not keep C<ev_loop> from
-example for its internal signal pipe: It is not visible to you as a user
+returning, ev_unref() after starting, and ev_ref() before stopping it. For
-and should not keep C<ev_loop> from exiting if the work is done. It is
+example, libev itself uses this for its internal signal pipe: It is not
-also an excellent way to do this for generic recurring timers or from
+visible to the libev user and should not keep C<ev_loop> from exiting if
-within third-party libraries. Just remember to unref after start and ref
+no event watchers registered by it are active. It is also an excellent
-before stop.
+way to do this for generic recurring timers or from within third-party
+libraries. Just remember to I<unref after start> and I<ref before stop>.
 =back
 =head1 ANATOMY OF A WATCHER
 A watcher is a structure that you create and register to record your
 interest in some event. For instance, if you want to wait for STDIN to
-become readable, you would create an ev_io watcher for that:
+become readable, you would create an C<ev_io> watcher for that:
   static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
   {
     ev_io_stop (w);
     ev_unloop (loop, EVUNLOOP_ALL);
 As long as your watcher is active (has been started but not stopped) you
 must not touch the values stored in it. Most specifically you must never
 reinitialise it or call its set method.
-You cna check wether an event is active by calling the C<ev_is_active
+You cna check whether an event is active by calling the C<ev_is_active
-(watcher *)> macro. To see wether an event is outstanding (but the
+(watcher *)> macro. To see whether an event is outstanding (but the
 callback for it has not been called yet) you cna use the C<ev_is_pending
 (watcher *)> macro.
 Each and every callback receives the event loop pointer as first, the
 registered watcher structure as second, and a bitset of received events as
 (you can receive multiple events at the same time). The possible bit masks
 are:
 =over 4
-=item EV_READ
+=item C<EV_READ>
-=item EV_WRITE
+=item C<EV_WRITE>
-The file descriptor in the ev_io watcher has become readable and/or
+The file descriptor in the C<ev_io> watcher has become readable and/or
 writable.
-=item EV_TIMEOUT
+=item C<EV_TIMEOUT>
-The ev_timer watcher has timed out.
+The C<ev_timer> watcher has timed out.
-=item EV_PERIODIC
+=item C<EV_PERIODIC>
-The ev_periodic watcher has timed out.
+The C<ev_periodic> watcher has timed out.
-=item EV_SIGNAL
+=item C<EV_SIGNAL>
-The signal specified in the ev_signal watcher has been received by a thread.
+The signal specified in the C<ev_signal> watcher has been received by a thread.
-=item EV_CHILD
+=item C<EV_CHILD>
-The pid specified in the ev_child watcher has received a status change.
+The pid specified in the C<ev_child> watcher has received a status change.
-=item EV_IDLE
+=item C<EV_IDLE>
-The ev_idle watcher has determined that you have nothing better to do.
+The C<ev_idle> watcher has determined that you have nothing better to do.
-=item EV_PREPARE
+=item C<EV_PREPARE>
-=item EV_CHECK
+=item C<EV_CHECK>
-All ev_prepare watchers are invoked just I<before> C<ev_loop> starts
+All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
-to gather new events, and all ev_check watchers are invoked just after
+to gather new events, and all C<ev_check> watchers are invoked just after
 C<ev_loop> has gathered them, but before it invokes any callbacks for any
 received events. Callbacks of both watcher types can start and stop as
 many watchers as they want, and all of them will be taken into account
-(for example, a ev_prepare watcher might start an idle watcher to keep
+(for example, a C<ev_prepare> watcher might start an idle watcher to keep
 C<ev_loop> from blocking).
-=item EV_ERROR
+=item C<EV_ERROR>
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev
 ran out of memory, a file descriptor was found to be closed or any other
 problem. You best act on it by reporting the problem and somehow coping
 =head1 WATCHER TYPES
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
-=head2 struct ev_io - is my file descriptor readable or writable
+=head2 C<ev_io> - is this file descriptor readable or writable
-I/O watchers check wether a file descriptor is readable or writable
+I/O watchers check whether a file descriptor is readable or writable
 in each iteration of the event loop (This behaviour is called
 level-triggering because you keep receiving events as long as the
 condition persists. Remember you cna stop the watcher if you don't want to
 act on the event and neither want to receive future events).
+In general you can register as many read and/or write event watchers oer
+fd as you want (as long as you don't confuse yourself). Setting all file
+descriptors to non-blocking mode is also usually a good idea (but not
+required if you know what you are doing).
+You have to be careful with dup'ed file descriptors, though. Some backends
+(the linux epoll backend is a notable example) cannot handle dup'ed file
+descriptors correctly if you register interest in two or more fds pointing
+to the same file/socket etc. description.
+If you must do this, then force the use of a known-to-be-good backend
+(at the time of this writing, this includes only EVMETHOD_SELECT and
+EVMETHOD_POLL).
 =over 4
 =item ev_io_init (ev_io *, callback, int fd, int events)
 =item ev_io_set (ev_io *, int fd, int events)
-Configures an ev_io watcher. The fd is the file descriptor to rceeive
+Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
 events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
 EV_WRITE> to receive the given events.
 =back
-=head2 struct ev_timer - relative and optionally recurring timeouts
+=head2 C<ev_timer> - relative and optionally recurring timeouts
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 The timers are based on real time, that is, if you register an event that
 times out after an hour and youreset your system clock to last years
 time, it will still time out after (roughly) and hour. "Roughly" because
 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
+The relative timeouts are calculated relative to the C<ev_now ()>
+time. This is usually the right thing as this timestamp refers to the time
+of the event triggering whatever timeout you are modifying/starting.  If
+you suspect event processing to be delayed and you *need* to base the timeout
+ion the current time, use something like this to adjust for this:
+   ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
 =over 4
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 =item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
 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
+configure an C<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.
 =back
-=head2 ev_periodic
+=head2 C<ev_periodic> - to cron or not to cron it
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
-Unlike ev_timer's, they are not based on real time (or relative time)
+Unlike C<ev_timer>'s, they are not based on real time (or relative time)
 but on wallclock time (absolute time). You can tell a periodic watcher
 to trigger "at" some specific point in time. For example, if you tell a
 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
 + 10.>) and then reset your system clock to the last year, then it will
-take a year to trigger the event (unlike an ev_timer, which would trigger
+take a year to trigger the event (unlike an C<ev_timer>, which would trigger
 roughly 10 seconds later and of course not if you reset your system time
 again).
 They can also be used to implement vastly more complex timers, such as
 triggering an event on eahc midnight, local time.
    ev_periodic_set (&periodic, 0., 3600., 0);
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a
-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible
 by 3600.
 Another way to think about it (for the mathematically inclined) is that
-ev_periodic will try to run the callback in this mode at the next possible
+C<ev_periodic> will try to run the callback in this mode at the next possible
 time where C<time = at (mod interval)>, regardless of any time jumps.
 =item * manual reschedule mode (reschedule_cb = callback)
 In this mode the values for C<interval> and C<at> are both being
 ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
 NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions>. If you need
+periodic watcher, ever, or make any event loop modifications>. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
+to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
+Also, I<<this callback must always return a time that is later than the
+passed C<now> value >>. Not even C<now> itself will be ok.
 Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)>, e.g.:
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
 =back
-=head2 ev_signal - signal me when a signal gets signalled
+=head2 C<ev_signal> - signal me when a signal gets signalled
 Signal watchers will trigger an event when the process receives a specific
 signal one or more times. Even though signals are very asynchronous, libev
-will try its best to deliver signals synchronously, i.e. as part of the
+will try it's best to deliver signals synchronously, i.e. as part of the
 normal event processing, like any other event.
 You cna configure as many watchers as you like per signal. Only when the
 first watcher gets started will libev actually register a signal watcher
 with the kernel (thus it coexists with your own signal handlers as long
 Configures the watcher to trigger on the given signal number (usually one
 of the C<SIGxxx> constants).
 =back
-=head2 ev_child - wait for pid status changes
+=head2 C<ev_child> - wait for pid status changes
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).
 =over 4
 the status word (use the macros from C<sys/wait.h>). The C<rpid> member
 contains the pid of the process causing the status change.
 =back
-=head2 ev_idle - when you've got nothing better to do
+=head2 C<ev_idle> - when you've got nothing better to do
 Idle watchers trigger events when there are no other I/O or timer (or
 periodic) events pending. That is, as long as your process is busy
 handling sockets or timeouts it will not be called. But when your process
 is idle all idle watchers are being called again and again - until
 Their main purpose is to integrate other event mechanisms into libev. This
 could be used, for example, to track variable changes, implement your own
 watchers, integrate net-snmp or a coroutine library and lots more.
 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
+to be watched by the other library, registering C<ev_io> watchers for them
-and starting an ev_timer watcher for any timeouts (many libraries provide
+and starting an C<ev_timer> watcher for any timeouts (many libraries provide
 just this functionality). Then, in the check watcher you check for any
 events that occured (by making your callbacks set soem flags for example)
 and call back into the library.
 As another example, the perl Coro module uses these hooks to integrate
 watchers. This is useful if you want to wait for a single event on an fd
 or timeout without havign to allocate/configure/start/stop/free one or
 more watchers yourself.
 If C<fd> is less than 0, then no I/O watcher will be started and events is
-ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set
+ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and C<events> set
 will be craeted and started.
 If C<timeout> is less than 0, then no timeout watcher will be
-started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat
+started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and repeat
 = 0) will be started.
 The callback has the type C<void (*cb)(int revents, void *arg)> and
-gets passed an events set (normally a combination of EV_ERROR, EV_READ,
+gets passed an events set (normally a combination of C<EV_ERROR>, C<EV_READ>,
-EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:
+C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> value passed to C<ev_once>:
   static void stdin_ready (int revents, void *arg)
   {
     if (revents & EV_TIMEOUT)
       /* doh, nothing entered */

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Comparing libev/ev.pod (file contents): Revision 1.1 by root, Mon Nov 12 07:58:13 2007 UTC vs. Revision 1.12 by root, Mon Nov 12 08:35:18 2007 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.1 by root, Mon Nov 12 07:58:13 2007 UTC vs.
Revision 1.12 by root, Mon Nov 12 08:35:18 2007 UTC