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

Comparing libev/ev.pod (file contents):
Revision 1.182 by root, Fri Sep 19 03:52:56 2008 UTC vs.
Revision 1.183 by root, Tue Sep 23 08:37:38 2008 UTC

 Please note that epoll sometimes generates spurious notifications, so you
 need to use non-blocking I/O or other means to avoid blocking when no data
 (or space) is available.
 Best performance from this backend is achieved by not unregistering all
-watchers for a file descriptor until it has been closed, if possible, i.e.
+watchers for a file descriptor until it has been closed, if possible,
-keep at least one watcher active per fd at all times.
+i.e. keep at least one watcher active per fd at all times. Stopping and
+starting a watcher (without re-setting it) also usually doesn't cause
+extra overhead.
 While nominally embeddable in other event loops, this feature is broken in
 all kernel versions tested so far.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
-Kqueue deserves special mention, as at the time of this writing, it
+Kqueue deserves special mention, as at the time of this writing, it was
-was broken on all BSDs except NetBSD (usually it doesn't work reliably
+broken on all BSDs except NetBSD (usually it doesn't work reliably with
-with anything but sockets and pipes, except on Darwin, where of course
+anything but sockets and pipes, except on Darwin, where of course it's
-it's completely useless). For this reason it's not being "auto-detected"
+completely useless). For this reason it's not being "auto-detected" unless
-unless you explicitly specify it explicitly in the flags (i.e. using
+you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
-C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
+libev was compiled on a known-to-be-good (-enough) system like NetBSD.
-system like NetBSD.
 You still can embed kqueue into a normal poll or select backend and use it
 only for sockets (after having made sure that sockets work with kqueue on
 the target platform). See C<ev_embed> watchers for more info.
 It scales in the same way as the epoll backend, but the interface to the
 kernel is more efficient (which says nothing about its actual speed, of
 course). While stopping, setting and starting an I/O watcher does never
 cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
-two event changes per incident, support for C<fork ()> is very bad and it
+two event changes per incident. Support for C<fork ()> is very bad and it
 drops fds silently in similarly hard-to-detect cases.
 This backend usually performs well under most conditions.
 While nominally embeddable in other event loops, this doesn't work
 everywhere, so you might need to test for this. And since it is broken
 almost everywhere, you should only use it when you have a lot of sockets
 (for which it usually works), by embedding it into another event loop
-(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
+(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
-sockets.
+using it only for sockets.
 This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
 C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
 C<NOTE_EOF>.
 While this backend scales well, it requires one system call per active
 file descriptor per loop iteration. For small and medium numbers of file
 descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
 might perform better.
-On the positive side, ignoring the spurious readiness notifications, this
+On the positive side, with the exception of the spurious readiness
-backend actually performed to specification in all tests and is fully
+notifications, this backend actually performed fully to specification
-embeddable, which is a rare feat among the OS-specific backends.
+in all tests and is fully embeddable, which is a rare feat among the
+OS-specific backends.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
 C<EVBACKEND_POLL>.
 =item C<EVBACKEND_ALL>
 If one or more of these are or'ed into the flags value, then only these
 backends will be tried (in the reverse order as listed here). If none are
 specified, all backends in C<ev_recommended_backends ()> will be tried.
-The most typical usage is like this:
+Example: This is the most typical usage.
    if (!ev_default_loop (0))
      fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
-Restrict libev to the select and poll backends, and do not allow
+Example: Restrict libev to the select and poll backends, and do not allow
 environment settings to be taken into account:
    ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
-Use whatever libev has to offer, but make sure that kqueue is used if
+Example: Use whatever libev has to offer, but make sure that kqueue is
-available (warning, breaks stuff, best use only with your own private
+used if available (warning, breaks stuff, best use only with your own
-event loop and only if you know the OS supports your types of fds):
+private event loop and only if you know the OS supports your types of
+fds):
    ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
 =item struct ev_loop *ev_loop_new (unsigned int flags)
 =item ev_loop_fork (loop)
 Like C<ev_default_fork>, but acts on an event loop created by
 C<ev_loop_new>. Yes, you have to call this on every allocated event loop
-after fork, and how you do this is entirely your own problem.
+after fork that you want to re-use in the child, and how you do this is
+entirely your own problem.
 =item int ev_is_default_loop (loop)
-Returns true when the given loop actually is the default loop, false otherwise.
+Returns true when the given loop is, in fact, the default loop, and false
+otherwise.
 =item unsigned int ev_loop_count (loop)
 Returns the count of loop iterations for the loop, which is identical to
 the number of times libev did poll for new events. It starts at C<0> and
 If the flags argument is specified as C<0>, it will not return until
 either no event watchers are active anymore or C<ev_unloop> was called.
 Please note that an explicit C<ev_unloop> is usually better than
 relying on all watchers to be stopped when deciding when a program has
-finished (especially in interactive programs), but having a program that
+finished (especially in interactive programs), but having a program
-automatically loops as long as it has to and no longer by virtue of
+that automatically loops as long as it has to and no longer by virtue
-relying on its watchers stopping correctly is a thing of beauty.
+of relying on its watchers stopping correctly, that is truly a thing of
+beauty.
 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
+those events and any already outstanding ones, but will not block your
-case there are no events and will return after one iteration of the loop.
+process in 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
-necessary) and will handle those and any outstanding ones. It will block
+necessary) and will handle those and any already outstanding ones. It
-your process until at least one new event arrives, and will return after
+will block your process until at least one new event arrives (which could
-one iteration of the loop. This is useful if you are waiting for some
+be an event internal to libev itself, so there is no guarentee that a
-external event in conjunction with something not expressible using other
+user-registered callback will be called), and will return after one
+iteration of the loop.
+This is useful if you are waiting for some external event in conjunction
+with something not expressible using other libev watchers (i.e. "roll your
-libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
+own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
 usually a better approach for this kind of thing.
 Here are the gory details of what C<ev_loop> does:
    - Before the first iteration, call any pending watchers.
      any active watchers at all will result in not sleeping).
    - Sleep if the I/O and timer collect interval say so.
    - Block the process, waiting for any events.
    - Queue all outstanding I/O (fd) events.
    - Update the "event loop time" (ev_now ()), and do time jump adjustments.
-   - Queue all outstanding timers.
+   - Queue all expired timers.
-   - Queue all outstanding periodics.
+   - Queue all expired periodics.
    - Unless any events are pending now, queue all idle watchers.
    - Queue all check watchers.
    - Call all queued watchers in reverse order (i.e. check watchers first).
      Signals and child watchers are implemented as I/O watchers, and will
      be handled here by queueing them when their watcher gets executed.
 =item ev_unref (loop)
 Ref/unref can be used to add or remove a reference count on the event
 loop: Every watcher keeps one reference, and as long as the reference
-count is nonzero, C<ev_loop> will not return on its own. If you have
+count is nonzero, C<ev_loop> will not return on its own.
-a watcher you never unregister that should not keep C<ev_loop> from
+If you have a watcher you never unregister that should not keep C<ev_loop>
-returning, ev_unref() after starting, and ev_ref() before stopping it. For
+from returning, call ev_unref() after starting, and ev_ref() before
+stopping it.
-example, libev itself uses this for its internal signal pipe: It is not
+As an example, libev itself uses this for its internal signal pipe: It is
-visible to the libev user and should not keep C<ev_loop> from exiting if
+not visible to the libev user and should not keep C<ev_loop> from exiting
-no event watchers registered by it are active. It is also an excellent
+if no event watchers registered by it are active. It is also an excellent
 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>
 (but only if the watcher wasn't active before, or was active before,
 respectively).
 Setting these to a higher value (the C<interval> I<must> be >= C<0>)
 allows libev to delay invocation of I/O and timer/periodic callbacks
 to increase efficiency of loop iterations (or to increase power-saving
 opportunities).
-The background is that sometimes your program runs just fast enough to
+The idea is that sometimes your program runs just fast enough to handle
-handle one (or very few) event(s) per loop iteration. While this makes
+one (or very few) event(s) per loop iteration. While this makes the
-the program responsive, it also wastes a lot of CPU time to poll for new
+program responsive, it also wastes a lot of CPU time to poll for new
 events, especially with backends like C<select ()> which have a high
 overhead for the actual polling but can deliver many events at once.
 By setting a higher I<io collect interval> you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 C<ev_timer>) will be not affected. Setting this to a non-null value will
 introduce an additional C<ev_sleep ()> call into most loop iterations.
 Likewise, by setting a higher I<timeout collect interval> you allow libev
 to spend more time collecting timeouts, at the expense of increased
-latency (the watcher callback will be called later). C<ev_io> watchers
+latency/jitter/inexactness (the watcher callback will be called
-will not be affected. Setting this to a non-null value will not introduce
+later). C<ev_io> watchers will not be affected. Setting this to a non-null
-any overhead in libev.
+value will not introduce any overhead in libev.
 Many (busy) programs can usually benefit by setting the I/O collect
 interval to a value near C<0.1> or so, which is often enough for
 interactive servers (of course not for games), likewise for timeouts. It
 usually doesn't make much sense to set it to a lower value than C<0.01>,
 they fire on, say, one-second boundaries only.
 =item ev_loop_verify (loop)
 This function only does something when C<EV_VERIFY> support has been
-compiled in. It tries to go through all internal structures and checks
+compiled in. which is the default for non-minimal builds. It tries to go
-them for validity. If anything is found to be inconsistent, it will print
+through all internal structures and checks them for validity. If anything
-an error message to standard error and call C<abort ()>.
+is found to be inconsistent, it will print an error message to standard
+error and call C<abort ()>.
 This can be used to catch bugs inside libev itself: under normal
 circumstances, this function will never abort as of course libev keeps its
 data structures consistent.
 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
 with the watcher being stopped.
-Libev will usually signal a few "dummy" events together with an error,
+Libev will usually signal a few "dummy" events together with an error, for
-for example it might indicate that a fd is readable or writable, and if
+example it might indicate that a fd is readable or writable, and if your
-your callbacks is well-written it can just attempt the operation and cope
+callbacks is well-written it can just attempt the operation and cope with
-with the error from read() or write(). This will not work in multi-threaded
+the error from read() or write(). This will not work in multi-threaded
-programs, though, so beware.
+programs, though, as the fd could already be closed and reused for another
+thing, so beware.
 =back
 =head2 GENERIC WATCHER FUNCTIONS
 (or never started) and there are no pending events outstanding.
 The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
 int revents)>.
+Example: Initialise an C<ev_io> watcher in two steps.
+   ev_io w;
+   ev_init (&w, my_cb);
+   ev_io_set (&w, STDIN_FILENO, EV_READ);
 =item C<ev_TYPE_set> (ev_TYPE *, [args])
 This macro initialises the type-specific parts of a watcher. You need to
 call C<ev_init> at least once before you call this macro, but you can
 call C<ev_TYPE_set> any number of times. You must not, however, call this
 difference to the C<ev_init> macro).
 Although some watcher types do not have type-specific arguments
 (e.g. C<ev_prepare>) you still need to call its C<set> macro.
+See C<ev_init>, above, for an example.
 =item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
 This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
 calls into a single call. This is the most convenient method to initialise
 a watcher. The same limitations apply, of course.
+Example: Initialise and set an C<ev_io> watcher in one step.
+   ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
 =item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
 Starts (activates) the given watcher. Only active watchers will receive
 events. If the watcher is already active nothing will happen.
+Example: Start the C<ev_io> watcher that is being abused as example in this
+whole section.
+   ev_io_start (EV_DEFAULT_UC, &w);
 =item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
 Stops the given watcher again (if active) and clears the pending
 status. It is possible that stopped watchers are pending (for example,
 =item ev_invoke (loop, ev_TYPE *watcher, int revents)
 Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
 C<loop> nor C<revents> need to be valid as long as the watcher callback
-can deal with that fact.
+can deal with that fact, as both are simply passed through to the
+callback.
 =item int ev_clear_pending (loop, ev_TYPE *watcher)
-If the watcher is pending, this function returns clears its pending status
+If the watcher is pending, this function clears its pending status and
-and returns its C<revents> bitset (as if its callback was invoked). If the
+returns its C<revents> bitset (as if its callback was invoked). If the
 watcher isn't pending it does nothing and returns C<0>.
+Sometimes it can be useful to "poll" a watcher instead of waiting for its
+callback to be invoked, which can be accomplished with this function.
 =back
 =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
 Each watcher has, by default, a member C<void *data> that you can change
-and read at any time, libev will completely ignore it. This can be used
+and read at any time: libev will completely ignore it. This can be used
 to associate arbitrary data with your watcher. If you need more data and
 don't want to allocate memory and store a pointer to it in that data
 member, you can also "subclass" the watcher type and provide your own
 data:
      ev_timer t2;
    }
 In this case getting the pointer to C<my_biggy> is a bit more
 complicated: Either you store the address of your C<my_biggy> struct
-in the C<data> member of the watcher, or you need to use some pointer
+in the C<data> member of the watcher (for woozies), or you need to use
-arithmetic using C<offsetof> inside your watchers:
+some pointer arithmetic using C<offsetof> inside your watchers (for real
+programmers):
    #include <stddef.h>
    static void
    t1_cb (EV_P_ struct ev_timer *w, int revents)
 In general you can register as many read and/or write event watchers per
 fd as you want (as long as you don't confuse yourself). Setting all file
 descriptors to non-blocking mode is also usually a good idea (but not
 required if you know what you are doing).
-If you must do this, then force the use of a known-to-be-good backend
+If you cannot use non-blocking mode, then force the use of a
-(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
+known-to-be-good backend (at the time of this writing, this includes only
-C<EVBACKEND_POLL>).
+C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
 Another thing you have to watch out for is that it is quite easy to
 receive "spurious" readiness notifications, that is your callback might
 be called with C<EV_READ> but a subsequent C<read>(2) will actually block
 because there is no data. Not only are some backends known to create a
 lot of those (for example Solaris ports), it is very easy to get into
 this situation even with a relatively standard program structure. Thus
 it is best to always use non-blocking I/O: An extra C<read>(2) returning
 C<EAGAIN> is far preferable to a program hanging until some data arrives.
-If you cannot run the fd in non-blocking mode (for example you should not
+If you cannot run the fd in non-blocking mode (for example you should
-play around with an Xlib connection), then you have to separately re-test
+not play around with an Xlib connection), then you have to separately
-whether a file descriptor is really ready with a known-to-be good interface
+re-test whether a file descriptor is really ready with a known-to-be good
-such as poll (fortunately in our Xlib example, Xlib already does this on
+interface such as poll (fortunately in our Xlib example, Xlib already
-its own, so its quite safe to use).
+does this on its own, so its quite safe to use). Some people additionally
+use C<SIGALRM> and an interval timer, just to be sure you won't block
+indefinitely.
+But really, best use non-blocking mode.
 =head3 The special problem of disappearing file descriptors
 Some backends (e.g. kqueue, epoll) need to be told about closing a file
-descriptor (either by calling C<close> explicitly or by any other means,
+descriptor (either due to calling C<close> explicitly or any other means,
-such as C<dup>). The reason is that you register interest in some file
+such as C<dup2>). The reason is that you register interest in some file
 descriptor, but when it goes away, the operating system will silently drop
 this interest. If another file descriptor with the same number then is
 registered with libev, there is no efficient way to see that this is, in
 fact, a different file descriptor.
 enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
 C<EVBACKEND_POLL>.
 =head3 The special problem of SIGPIPE
-While not really specific to libev, it is easy to forget about SIGPIPE:
+While not really specific to libev, it is easy to forget about C<SIGPIPE>:
 when writing to a pipe whose other end has been closed, your program gets
-send a SIGPIPE, which, by default, aborts your program. For most programs
+sent a SIGPIPE, which, by default, aborts your program. For most programs
 this is sensible behaviour, for daemons, this is usually undesirable.
 So when you encounter spurious, unexplained daemon exits, make sure you
 ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
 somewhere, as that would have given you a big clue).
 =item ev_io_init (ev_io *, callback, int fd, int events)
 =item ev_io_set (ev_io *, int fd, int events)
 Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
-receive events for and events is either C<EV_READ>, C<EV_WRITE> or
+receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
-C<EV_READ | EV_WRITE> to receive the given events.
+C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
 =item int fd [read-only]
 The file descriptor being watched.
    static void
    stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
    {
       ev_io_stop (loop, w);
-     .. read from stdin here (or from w->fd) and haqndle any I/O errors
+     .. read from stdin here (or from w->fd) and handle any I/O errors
    }
    ...
    struct ev_loop *loop = ev_default_init (0);
    struct ev_io stdin_readable;
 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 you reset your system clock to January last
-year, it will still time out after (roughly) and hour. "Roughly" because
+year, it will still time out after (roughly) one hour. "Roughly" because
 detecting time jumps is hard, and some inaccuracies are unavoidable (the
 monotonic clock option helps a lot here).
-The callback is guaranteed to be invoked only after its timeout has passed,
+The callback is guaranteed to be invoked only I<after> its timeout has
-but if multiple timers become ready during the same loop iteration then
+passed, but if multiple timers become ready during the same loop iteration
-order of execution is undefined.
+then order of execution is undefined.
 =head3 The special problem of time updates
 Establishing the current time is a costly operation (it usually takes at
 least two system calls): EV therefore updates its idea of the current
-time only before and after C<ev_loop> polls for new events, which causes
+time only before and after C<ev_loop> collects new events, which causes a
-a growing difference between C<ev_now ()> and C<ev_time ()> when handling
+growing difference between C<ev_now ()> and C<ev_time ()> when handling
-lots of events.
+lots of events in one iteration.
 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 I<need> to base the
    ev_timer_again (loop, timer);
 This is more slightly efficient then stopping/starting the timer each time
 you want to modify its timeout value.
+Note, however, that it is often even more efficient to remember the
+time of the last activity and let the timer time-out naturally. In the
+callback, you then check whether the time-out is real, or, if there was
+some activity, you reschedule the watcher to time-out in "last_activity +
+timeout - ev_now ()" seconds.
 =item ev_tstamp repeat [read-write]
 The current C<repeat> value. Will be used each time the watcher times out
-or C<ev_timer_again> is called and determines the next timeout (if any),
+or C<ev_timer_again> is called, and determines the next timeout (if any),
 which is also when any modifications are taken into account.
 =back
 =head3 Examples
 to trigger the event (unlike an C<ev_timer>, which would still trigger
 roughly 10 seconds later as it uses a relative timeout).
 C<ev_periodic>s can also be used to implement vastly more complex timers,
 such as triggering an event on each "midnight, local time", or other
-complicated, rules.
+complicated rules.
 As with timers, the callback is guaranteed to be invoked only when the
 time (C<at>) has passed, but if multiple periodic timers become ready
-during the same loop iteration then order of execution is undefined.
+during the same loop iteration, then order of execution is undefined.
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
 Lots of arguments, lets sort it out... There are basically three modes of
-operation, and we will explain them from simplest to complex:
+operation, and we will explain them from simplest to most complex:
 =over 4
 =item * absolute timer (at = time, interval = reschedule_cb = 0)
 In this configuration the watcher triggers an event after the wall clock
-time C<at> has passed and doesn't repeat. It will not adjust when a time
+time C<at> has passed. It will not repeat and will not adjust when a time
 jump occurs, that is, if it is to be run at January 1st 2011 then it will
-run when the system time reaches or surpasses this time.
+only run when the system clock reaches or surpasses this time.
 =item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
 In this mode the watcher will always be scheduled to time out at the next
 C<at + N * interval> time (for some integer N, which can also be negative)
 and then repeat, regardless of any time jumps.
-This can be used to create timers that do not drift with respect to system
+This can be used to create timers that do not drift with respect to the
-time, for example, here is a C<ev_periodic> that triggers each hour, on
+system clock, for example, here is a C<ev_periodic> that triggers each
-the hour:
+hour, on the hour:
    ev_periodic_set (&periodic, 0., 3600., 0);
 This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the callback will be called when the system time shows a
 =back
 =head3 Examples
 Example: Call a callback every hour, or, more precisely, whenever the
-system clock is divisible by 3600. The callback invocation times have
+system time is divisible by 3600. The callback invocation times have
 potentially a lot of jitter, but good long-term stability.
    static void
    clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
    {
    #include <math.h>
    static ev_tstamp
    my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
    {
-     return fmod (now, 3600.) + 3600.;
+     return now + (3600. - fmod (now, 3600.));
    }
    ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
 Example: Call a callback every hour, starting now:
 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 it's best to deliver signals synchronously, i.e. as part of the
 normal event processing, like any other event.
+If you want signals asynchronously, just use C<sigaction> as you would
+do without libev and forget about sharing the signal. You can even use
+C<ev_async> from a signal handler to synchronously wake up an event loop.
 You can configure as many watchers as you like per signal. Only when the
-first watcher gets started will libev actually register a signal watcher
+first watcher gets started will libev actually register a signal handler
-with the kernel (thus it coexists with your own signal handlers as long
+with the kernel (thus it coexists with your own signal handlers as long as
-as you don't register any with libev). Similarly, when the last signal
+you don't register any with libev for the same signal). Similarly, when
-watcher for a signal is stopped libev will reset the signal handler to
+the last signal watcher for a signal is stopped, libev will reset the
-SIG_DFL (regardless of what it was set to before).
+signal handler to SIG_DFL (regardless of what it was set to before).
 If possible and supported, libev will install its handlers with
 C<SA_RESTART> behaviour enabled, so system calls should not be unduly
 interrupted. If you have a problem with system calls getting interrupted by
 signals you can block all signals in an C<ev_check> watcher and unblock
 =head2 C<ev_child> - watch out for process status changes
 Child watchers trigger when your process receives a SIGCHLD in response to
-some child status changes (most typically when a child of yours dies). It
+some child status changes (most typically when a child of yours dies or
-is permissible to install a child watcher I<after> the child has been
+exits). It is permissible to install a child watcher I<after> the child
-forked (which implies it might have already exited), as long as the event
+has been forked (which implies it might have already exited), as long
-loop isn't entered (or is continued from a watcher).
+as the event loop isn't entered (or is continued from a watcher), i.e.,
+forking and then immediately registering a watcher for the child is fine,
+but forking and registering a watcher a few event loop iterations later is
+not.
 Only the default event loop is capable of handling signals, and therefore
 you can only register child watchers in the default event loop.
 =head3 Process Interaction
 the stat buffer having unspecified contents.
 The path I<should> be absolute and I<must not> end in a slash. If it is
 relative and your working directory changes, the behaviour is undefined.
-Since there is no standard to do this, the portable implementation simply
+Since there is no standard kernel interface to do this, the portable
-calls C<stat (2)> regularly on the path to see if it changed somehow. You
+implementation simply calls C<stat (2)> regularly on the path to see if
-can specify a recommended polling interval for this case. If you specify
+it changed somehow. You can specify a recommended polling interval for
-a polling interval of C<0> (highly recommended!) then a I<suitable,
+this case. If you specify a polling interval of C<0> (highly recommended!)
-unspecified default> value will be used (which you can expect to be around
+then a I<suitable, unspecified default> value will be used (which
-five seconds, although this might change dynamically). Libev will also
+you can expect to be around five seconds, although this might change
-impose a minimum interval which is currently around C<0.1>, but thats
+dynamically). Libev will also impose a minimum interval which is currently
-usually overkill.
+around C<0.1>, but thats usually overkill.
 This watcher type is not meant for massive numbers of stat watchers,
 as even with OS-supported change notifications, this can be
 resource-intensive.
-At the time of this writing, only the Linux inotify interface is
+At the time of this writing, the only OS-specific interface implemented
-implemented (implementing kqueue support is left as an exercise for the
+is the Linux inotify interface (implementing kqueue support is left as
-reader, note, however, that the author sees no way of implementing ev_stat
+an exercise for the reader. Note, however, that the author sees no way
-semantics with kqueue). Inotify will be used to give hints only and should
+of implementing C<ev_stat> semantics with kqueue).
-not change the semantics of C<ev_stat> watchers, which means that libev
-sometimes needs to fall back to regular polling again even with inotify,
-but changes are usually detected immediately, and if the file exists there
-will be no polling.
 =head3 ABI Issues (Largefile Support)
 Libev by default (unless the user overrides this) uses the default
 compilation environment, which means that on systems with large file
 file interfaces available by default (as e.g. FreeBSD does) and not
 optional. Libev cannot simply switch on large file support because it has
 to exchange stat structures with application programs compiled using the
 default compilation environment.
-=head3 Inotify
+=head3 Inotify and Kqueue
 When C<inotify (7)> support has been compiled into libev (generally only
-available on Linux) and present at runtime, it will be used to speed up
+available with Linux) and present at runtime, it will be used to speed up
 change detection where possible. The inotify descriptor will be created lazily
 when the first C<ev_stat> watcher is being started.
 Inotify presence does not change the semantics of C<ev_stat> watchers
 except that changes might be detected earlier, and in some cases, to avoid
 making regular C<stat> calls. Even in the presence of inotify support
-there are many cases where libev has to resort to regular C<stat> polling.
+there are many cases where libev has to resort to regular C<stat> polling,
+but as long as the path exists, libev usually gets away without polling.
-(There is no support for kqueue, as apparently it cannot be used to
+There is no support for kqueue, as apparently it cannot be used to
 implement this functionality, due to the requirement of having a file
-descriptor open on the object at all times).
+descriptor open on the object at all times, and detecting renames, unlinks
+etc. is difficult.
 =head3 The special problem of stat time resolution
 The C<stat ()> system call only supports full-second resolution portably, and
-even on systems where the resolution is higher, many file systems still
+even on systems where the resolution is higher, most file systems still
 only support whole seconds.
 That means that, if the time is the only thing that changes, you can
 easily miss updates: on the first update, C<ev_stat> detects a change and
 calls your callback, which does something. When there is another update
-within the same second, C<ev_stat> will be unable to detect it as the stat
+within the same second, C<ev_stat> will be unable to detect unless the
-data does not change.
+stat data does change in other ways (e.g. file size).
 The solution to this is to delay acting on a change for slightly more
 than a second (or till slightly after the next full second boundary), using
 a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
 ev_timer_again (loop, w)>).
 C<path>. The C<interval> is a hint on how quickly a change is expected to
 be detected and should normally be specified as C<0> to let libev choose
 a suitable value. The memory pointed to by C<path> must point to the same
 path for as long as the watcher is active.
-The callback will receive C<EV_STAT> when a change was detected, relative
+The callback will receive an C<EV_STAT> event when a change was detected,
-to the attributes at the time the watcher was started (or the last change
+relative to the attributes at the time the watcher was started (or the
-was detected).
+last change was detected).
 =item ev_stat_stat (loop, ev_stat *)
 Updates the stat buffer immediately with new values. If you change the
 watched path in your callback, you could call this function to avoid
 =head2 C<ev_idle> - when you've got nothing better to do...
 Idle watchers trigger events when no other events of the same or higher
-priority are pending (prepare, check and other idle watchers do not
+priority are pending (prepare, check and other idle watchers do not count
-count).
+as receiving "events").
 That is, as long as your process is busy handling sockets or timeouts
 (or even signals, imagine) of the same or higher priority it will not be
 triggered. But when your process is idle (or only lower-priority watchers
 are pending), the idle watchers are being called once per event loop
    ev_idle_start (loop, idle_cb);
 =head2 C<ev_prepare> and C<ev_check> - customise your event loop!
-Prepare and check watchers are usually (but not always) used in tandem:
+Prepare and check watchers are usually (but not always) used in pairs:
 prepare watchers get invoked before the process blocks and check watchers
 afterwards.
 You I<must not> call C<ev_loop> or similar functions that enter
 the current event loop from either C<ev_prepare> or C<ev_check>
 those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
 C<ev_check> so if you have one watcher of each kind they will always be
 called in pairs bracketing the blocking call.
 Their main purpose is to integrate other event mechanisms into libev and
-their use is somewhat advanced. This could be used, for example, to track
+their use is somewhat advanced. They could be used, for example, to track
 variable changes, implement your own watchers, integrate net-snmp or a
 coroutine library and lots more. They are also occasionally useful if
 you cache some data and want to flush it before blocking (for example,
 in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
 watcher).
-This is done by examining in each prepare call which file descriptors need
+This is done by examining in each prepare call which file descriptors
-to be watched by the other library, registering C<ev_io> watchers for
+need to be watched by the other library, registering C<ev_io> watchers
-them and starting an C<ev_timer> watcher for any timeouts (many libraries
+for them and starting an C<ev_timer> watcher for any timeouts (many
-provide just this functionality). Then, in the check watcher you check for
+libraries provide exactly this functionality). Then, in the check watcher,
-any events that occurred (by checking the pending status of all watchers
+you check for any events that occurred (by checking the pending status
-and stopping them) and call back into the library. The I/O and timer
+of all watchers and stopping them) and call back into the library. The
-callbacks will never actually be called (but must be valid nevertheless,
+I/O and timer callbacks will never actually be called (but must be valid
-because you never know, you know?).
+nevertheless, because you never know, you know?).
 As another example, the Perl Coro module uses these hooks to integrate
 coroutines into libev programs, by yielding to other active coroutines
 during each prepare and only letting the process block if no coroutines
 are ready to run (it's actually more complicated: it only runs coroutines
 loop from blocking if lower-priority coroutines are active, thus mapping
 low-priority coroutines to idle/background tasks).
 It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
 priority, to ensure that they are being run before any other watchers
+after the poll (this doesn't matter for C<ev_prepare> watchers).
-after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
+Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
-too) should not activate ("feed") events into libev. While libev fully
+activate ("feed") events into libev. While libev fully supports this, they
-supports this, they might get executed before other C<ev_check> watchers
+might get executed before other C<ev_check> watchers did their job. As
-did their job. As C<ev_check> watchers are often used to embed other
+C<ev_check> watchers are often used to embed other (non-libev) event
-(non-libev) event loops those other event loops might be in an unusable
+loops those other event loops might be in an unusable state until their
-state until their C<ev_check> watcher ran (always remind yourself to
+C<ev_check> watcher ran (always remind yourself to coexist peacefully with
-coexist peacefully with others).
+others).
 =head3 Watcher-Specific Functions and Data Members
 =over 4
 =item ev_check_init (ev_check *, callback)
 Initialises and configures the prepare or check watcher - they have no
 parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
-macros, but using them is utterly, utterly and completely pointless.
+macros, but using them is utterly, utterly, utterly and completely
+pointless.
 =back
 =head3 Examples
    }
    // do not ever call adns_afterpoll
 Method 4: Do not use a prepare or check watcher because the module you
-want to embed is too inflexible to support it. Instead, you can override
+want to embed is not flexible enough to support it. Instead, you can
-their poll function.  The drawback with this solution is that the main
+override their poll function. The drawback with this solution is that the
-loop is now no longer controllable by EV. The C<Glib::EV> module does
+main loop is now no longer controllable by EV. The C<Glib::EV> module uses
-this.
+this approach, effectively embedding EV as a client into the horrible
+libglib event loop.
    static gint
    event_poll_func (GPollFD *fds, guint nfds, gint timeout)
    {
      int got_events = 0;
 prioritise I/O.
 As an example for a bug workaround, the kqueue backend might only support
 sockets on some platform, so it is unusable as generic backend, but you
 still want to make use of it because you have many sockets and it scales
-so nicely. In this case, you would create a kqueue-based loop and embed it
+so nicely. In this case, you would create a kqueue-based loop and embed
-into your default loop (which might use e.g. poll). Overall operation will
+it into your default loop (which might use e.g. poll). Overall operation
-be a bit slower because first libev has to poll and then call kevent, but
+will be a bit slower because first libev has to call C<poll> and then
-at least you can use both at what they are best.
+C<kevent>, but at least you can use both mechanisms for what they are
+best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
-As for prioritising I/O: rarely you have the case where some fds have
+As for prioritising I/O: under rare circumstances you have the case where
-to be watched and handled very quickly (with low latency), and even
+some fds have to be watched and handled very quickly (with low latency),
-priorities and idle watchers might have too much overhead. In this case
+and even priorities and idle watchers might have too much overhead. In
-you would put all the high priority stuff in one loop and all the rest in
+this case you would put all the high priority stuff in one loop and all
-a second one, and embed the second one in the first.
+the rest in a second one, and embed the second one in the first.
 As long as the watcher is active, the callback will be invoked every time
 there might be events pending in the embedded loop. The callback must then
 call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
 their callbacks (you could also start an idle watcher to give the embedded
 interested in that.
 Also, there have not currently been made special provisions for forking:
 when you fork, you not only have to call C<ev_loop_fork> on both loops,
 but you will also have to stop and restart any C<ev_embed> watchers
-yourself.
+yourself - but you can use a fork watcher to handle this automatically,
+and future versions of libev might do just that.
 Unfortunately, not all backends are embeddable, only the ones returned by
 C<ev_embeddable_backends> are, which, unfortunately, does not include any
 portable one.

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Comparing libev/ev.pod (file contents): Revision 1.182 by root, Fri Sep 19 03:52:56 2008 UTC vs. Revision 1.183 by root, Tue Sep 23 08:37:38 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.182 by root, Fri Sep 19 03:52:56 2008 UTC vs.
Revision 1.183 by root, Tue Sep 23 08:37:38 2008 UTC