do a lot of minor tweaking

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index e409a0391fc68b62df8cb5c88c80390e177bcd54..411fbb5f1a38cb0af2e56a0c39d6dc180df832bf 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -10,7 +10,7 @@ libev - a high performance full-featured event loop written in C
 
 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
 
 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
 
 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


@@ -27,29 +27,40 @@ 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
 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
 
 =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.
 
 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
+=head1 TIME REPRESENTATION

 
 

-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.
 
 called C<ev_tstamp>, which is what you should use too. It usually aliases
 to the double type in C.
 

+=head1 GLOBAL FUNCTIONS
+
+These functions can be called anytime, even before initialising the
+library in any way.
+

 =over 4
 
 =item ev_tstamp ev_time ()
 
 =over 4
 
 =item ev_tstamp ev_time ()
 

-Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+C<ev_now> function is usually faster and also often returns the timestamp
+you actually want to know.

 
 =item int ev_version_major ()
 
 
 =item int ev_version_major ()
 


@@ -61,7 +72,7 @@ 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.
 
 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.
 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.


@@ -69,10 +80,10 @@ 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
 =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
-here). If it returns zero when memory needs to be allocated, the library
-might abort or take some potentially destructive action. The default is
-your system realloc function.
+realloc C function, the semantics are identical). It is used to allocate
+and free memory (no surprises here). If it returns zero when memory
+needs to be allocated, the library might abort or take some potentially
+destructive action. The default is your system realloc function.

 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,
 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,


@@ -84,7 +95,7 @@ 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
 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).
 
 requested operation, or, if the condition doesn't go away, do bad stuff
 (such as abort).
 


@@ -97,10 +108,11 @@ 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
 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
-whatsoever, so if you mix calls to different event loops, make sure you
-lock (this is usually a bad idea, though, even if done right).
+in your main thread (or in a separate thread) and for each thread you
+create, you also create another event loop. Libev itself does no locking
+whatsoever, so if you mix calls to the same event loop in different
+threads, make sure you lock (this is usually a bad idea, though, even if
+done correctly, because it's hideous and inefficient).

 
 =over 4
 
 
 =over 4
 


@@ -115,36 +127,37 @@ 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
 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
 
 
 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).
 
 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
-at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this
-environment variable will override the flags completely. This is useful
-to try out specific backends to tets their performance, or to work around
-bugs.
+If this flag bit is ored into the flag value (or the program runs setuid
+or setgid) then libev will I<not> look at the environment variable
+C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
+override the flags completely if it is found in the environment. This is
+useful to try out specific backends to test their performance, or to work
+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
 
 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


@@ -163,7 +176,7 @@ undefined behaviour (or a failed assertion if assertions are enabled).
 
 Destroys the default loop again (frees all memory and kernel state
 etc.). This stops all registered event watchers (by not touching them in
 
 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)
 
 
 =item ev_loop_destroy (loop)
 


@@ -181,7 +194,7 @@ 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.
 
 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>:
 
 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>:
 


@@ -198,7 +211,7 @@ after fork, and how you do this is entirely your own problem.
 Returns one of the C<EVMETHOD_*> flags indicating the event backend in
 use.
 
 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
 
 Returns the current "event loop time", which is the time the event loop
 got events and started processing them. This timestamp does not change


@@ -217,36 +230,56 @@ 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
 
 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
 
 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.
 
 
 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.
 

+Here are the gory details of what ev_loop does:
+
+   1. If there are no active watchers (reference count is zero), return.
+   2. Queue and immediately call all prepare watchers.
+   3. If we have been forked, recreate the kernel state.
+   4. Update the kernel state with all outstanding changes.
+   5. Update the "event loop time".
+   6. Calculate for how long to block.
+   7. Block the process, waiting for events.
+   8. Update the "event loop time" and do time jump handling.
+   9. Queue all outstanding timers.
+  10. Queue all outstanding periodics.
+  11. If no events are pending now, queue all idle watchers.
+  12. Queue all check watchers.
+  13. Call all queued watchers in reverse order (i.e. check watchers first).
+  14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+      was used, return, otherwise continue with step #1.
+

 =item ev_unloop (loop, how)
 
 =item ev_unloop (loop, how)
 

-Can be used to make a call to C<ev_loop> return early. The C<how> argument
-must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop>
-call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop>
-calls return.
+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
+C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
+C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.

 
 =item ev_ref (loop)
 
 =item ev_unref (loop)
 
 
 =item ev_ref (loop)
 
 =item ev_unref (loop)
 

-Ref/unref can be used to add or remove a refcount on the event loop: Every
-watcher keeps one reference. If you have a long-runing watcher you never
-unregister that should not keep ev_loop from running, ev_unref() after
-starting, and ev_ref() before stopping it. Libev itself uses this for
-example for its internal signal pipe: It is not visible to you as a user
-and should not keep C<ev_loop> from exiting if the work is done. It is
-also an excellent way to do this for generic recurring timers or from
-within third-party libraries. Just remember to unref after start and ref
-before stop.
+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
+a watcher you never unregister that should not keep C<ev_loop> from
+returning, ev_unref() after starting, and ev_ref() before stopping it. For
+example, libev itself uses this for its internal signal pipe: It is not
+visible to the libev user and should not keep C<ev_loop> from exiting 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>.

 
 =back
 
 
 =back
 


@@ -254,7 +287,7 @@ before stop.
 
 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
 
 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)
   {
 
   static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
   {


@@ -293,61 +326,61 @@ 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.
 
 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
-(watcher *)> macro. To see wether an event is outstanding (but the
-callback for it has not been called yet) you cna use the C<ev_is_pending
+You can check whether an event is active by calling the C<ev_is_active
+(watcher *)> macro. To see whether an event is outstanding (but the
+callback for it has not been called yet) you can 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
 third argument.
 
 (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
 third argument.
 

-The rceeived events usually include a single bit per event type received
+The received events usually include a single bit per event type received

 (you can receive multiple events at the same time). The possible bit masks
 are:
 
 =over 4
 
 (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.
 
 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
-to gather new events, and all ev_check watchers are invoked just after
+All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
+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
 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).
 
 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
 
 An unspecified error has occured, the watcher has been stopped. This might
 happen because the watcher could not be properly started because libev


@@ -366,7 +399,7 @@ programs, though, so beware.
 =head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
 
 Each watcher has, by default, a member C<void *data> that you can change
 =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 cna 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
 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


@@ -398,37 +431,64 @@ have been omitted....
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
 
 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
 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
+condition persists. Remember you can stop the watcher if you don't want to

 act on the event and neither want to receive future events).
 
 act on the event and neither want to receive future events).
 

+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).
+
+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 underlying file/socket etc. description (that is, they share
+the same underlying "file open").
+
+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)
 
 =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
 
 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
 
 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
+times out after an hour and you reset your system clock to last years

 time, it will still time out after (roughly) and hour. "Roughly" because
 time, it will still time out after (roughly) and hour. "Roughly" because

-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some inaccuracies are unavoidable (the

 monotonic clock option helps a lot here).
 
 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 I<need> to base the timeout
+on the current time, use something like this to adjust for this:
+
+   ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+
+The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.
+

 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)


@@ -443,7 +503,7 @@ later, again, and again, until stopped manually.
 The timer itself will do a best-effort at avoiding drift, that is, if you
 configure a timer to trigger every 10 seconds, then it will trigger at
 exactly 10 second intervals. If, however, your program cannot keep up with
 The timer itself will do a best-effort at avoiding drift, that is, if you
 configure a timer to trigger every 10 seconds, then it will trigger at
 exactly 10 second intervals. If, however, your program cannot keep up with

-the timer (ecause it takes longer than those 10 seconds to do stuff) the
+the timer (because it takes longer than those 10 seconds to do stuff) the

 timer will not fire more than once per event loop iteration.
 
 =item ev_timer_again (loop)
 timer will not fire more than once per event loop iteration.
 
 =item ev_timer_again (loop)


@@ -460,30 +520,34 @@ 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
 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
 
 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

 
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 
 
 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
 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.
 
 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.
 

+As with timers, the callback is guarenteed to be invoked only when the
+time (C<at>) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
+

 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)


@@ -493,7 +557,6 @@ triggering an event on eahc midnight, local time.
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 
 Lots of arguments, lets sort it out... There are basically three modes of
 operation, and we will explain them from simplest to complex:
 

-

 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)
 =over 4
 
 =item * absolute timer (interval = reschedule_cb = 0)


@@ -516,11 +579,11 @@ time:
 
 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
 
 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
 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)
 time where C<time = at (mod interval)>, regardless of any time jumps.
 
 =item * manual reschedule mode (reschedule_cb = callback)


@@ -530,11 +593,12 @@ 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.
 
 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
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
+NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
+ever, or make any event loop modifications>. If you need to stop it,
+return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
+starting a prepare watcher).

 
 

-Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+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)
 ev_tstamp now)>, e.g.:
 
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)


@@ -547,10 +611,14 @@ It must return the next time to trigger, based on the passed time value
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
 

+NOTE: I<< This callback must always return a time that is later than the
+passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
+

 This can be used to create very complex timers, such as a timer that
 triggers on each midnight, local time. To do this, you would calculate the
 This can be used to create very complex timers, such as a timer that
 triggers on each midnight, local time. To do this, you would calculate the

-next midnight after C<now> and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
+next midnight after C<now> and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).

 
 =back
 
 
 =back
 


@@ -563,14 +631,14 @@ program when the crontabs have changed).
 
 =back
 
 
 =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
 
 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.
 
 normal event processing, like any other event.
 

-You cna configure as many watchers as you like per signal. Only when the
+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
 with the kernel (thus it coexists with your own signal handlers as long
 as you don't register any with libev). Similarly, when the last signal
 first watcher gets started will libev actually register a signal watcher
 with the kernel (thus it coexists with your own signal handlers as long
 as you don't register any with libev). Similarly, when the last signal


@@ -588,7 +656,7 @@ of the C<SIGxxx> constants).
 
 =back
 
 
 =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).
 
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).


@@ -602,18 +670,21 @@ some child status changes (most typically when a child of yours dies).
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see
 Configures the watcher to wait for status changes of process C<pid> (or
 I<any> process if C<pid> is specified as C<0>). The callback can look
 at the C<rstatus> member of the C<ev_child> watcher structure to see

-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.
+the status word (use the macros from C<sys/wait.h> and see your systems
+C<waitpid> documentation). The C<rpid> member contains the pid of the
+process causing the status change.

 
 =back
 
 
 =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
-stopped, that is, or your process receives more events.
+Idle watchers trigger events when there are no other events are pending
+(prepare, check and other idle watchers do not count). That is, as long
+as your process is busy handling sockets or timeouts (or even signals,
+imagine) it will not be triggered. But when your process is idle all idle
+watchers are being called again and again, once per event loop iteration -
+until stopped, that is, or your process receives more events and becomes
+busy.

 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.
 
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.


@@ -633,27 +704,33 @@ believe me.
 
 =back
 
 
 =back
 

-=head2 prepare and check - your hooks into the event loop
+=head2 C<ev_prepare> and C<ev_check> - customise your event loop

 
 

-Prepare and check watchers usually (but not always) are used in
-tandom. Prepare watchers get invoked before the process blocks and check
-watchers afterwards.
+Prepare and check watchers are usually (but not always) used in tandem:
+prepare watchers get invoked before the process blocks and check watchers
+afterwards.

 
 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
 
 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
-and starting an 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
+to be watched by the other library, registering C<ev_io> watchers for
+them 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 checking the pending status of all watchers
+and stopping them) and call back into the library. The I/O and timer
+callbacks will never actually be called (but must be valid 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
 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.
+are ready to run (it's actually more complicated: it only runs coroutines
+with priority higher than or equal to the event loop and one coroutine
+of lower priority, but only once, using idle watchers to keep the event
+loop from blocking if lower-priority coroutines are active, thus mapping
+low-priority coroutines to idle/background tasks).

 
 =over 4
 
 
 =over 4
 


@@ -663,13 +740,13 @@ are ready to run.
 
 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>
 
 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 pointless.
+macros, but using them is utterly, utterly and completely pointless.

 
 =back
 
 =head1 OTHER FUNCTIONS
 
 
 =back
 
 =head1 OTHER FUNCTIONS
 

-There are some other fucntions of possible interest. Described. Here. Now.
+There are some other functions of possible interest. Described. Here. Now.

 
 =over 4
 
 
 =over 4
 


@@ -678,40 +755,43 @@ There are some other fucntions of possible interest. Described. Here. Now.
 This function combines a simple timer and an I/O watcher, calls your
 callback on whichever event happens first and automatically stop both
 watchers. This is useful if you want to wait for a single event on an fd
 This function combines a simple timer and an I/O watcher, calls your
 callback on whichever event happens first and automatically stop both
 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
+or timeout without having to allocate/configure/start/stop/free one or

 more watchers yourself.
 
 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
-will be craeted and started.
+If C<fd> is less than 0, then no I/O watcher will be started and events
+is being 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
 
 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
-= 0) will be started.
+started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
+repeat = 0) will be started. While C<0> is a valid timeout, it is of
+dubious value.

 
 

-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,
-EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>:
+The callback has the type C<void (*cb)(int revents, void *arg)> and gets
+passed an C<revents> set like normal event callbacks (a combination of
+C<EV_ERROR>, C<EV_READ>, 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)
 
   static void stdin_ready (int revents, void *arg)
   {
     if (revents & EV_TIMEOUT)

-      /* doh, nothing entered */
+      /* doh, nothing entered */;

     else if (revents & EV_READ)
     else if (revents & EV_READ)

-      /* stdin might have data for us, joy! */
+      /* stdin might have data for us, joy! */;

   }
 
   }
 

-  ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+  ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);

 
 =item ev_feed_event (loop, watcher, int events)
 
 Feeds the given event set into the event loop, as if the specified event
 
 =item ev_feed_event (loop, watcher, int events)
 
 Feeds the given event set into the event loop, as if the specified event

-has happened for the specified watcher (which must be a pointer to an
-initialised but not necessarily active event watcher).
+had happened for the specified watcher (which must be a pointer to an
+initialised but not necessarily started event watcher).

 
 =item ev_feed_fd_event (loop, int fd, int revents)
 
 
 =item ev_feed_fd_event (loop, int fd, int revents)
 

-Feed an event on the given fd, as if a file descriptor backend detected it.
+Feed an event on the given fd, as if a file descriptor backend detected
+the given events it.

 
 =item ev_feed_signal_event (loop, int signum)
 
 
 =item ev_feed_signal_event (loop, int signum)
 


@@ -719,6 +799,37 @@ Feed an event as if the given signal occured (loop must be the default loop!).
 
 =back
 
 
 =back
 

+=head1 LIBEVENT EMULATION
+
+Libev offers a compatibility emulation layer for libevent. It cannot
+emulate the internals of libevent, so here are some usage hints:
+
+=over 4
+
+=item * Use it by including <event.h>, as usual.
+
+=item * The following members are fully supported: ev_base, ev_callback,
+ev_arg, ev_fd, ev_res, ev_events.
+
+=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).
+
+=item * Priorities are not currently supported. Initialising priorities
+will fail and all watchers will have the same priority, even though there
+is an ev_pri field.
+
+=item * Other members are not supported.
+
+=item * The libev emulation is I<not> ABI compatible to libevent, you need
+to use the libev header file and library.
+
+=back
+
+=head1 C++ SUPPORT
+
+TBD.
+

 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.
 =head1 AUTHOR
 
 Marc Lehmann <libev@schmorp.de>.