- add non-os-assisted ev_stat watcher

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 05bac9896ea08f8e6c9e49c1b1abe0d87cf4d183..3f4a06461c9a6eb09c06da51a47a5491594105bb 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -470,6 +470,7 @@ Example: for some weird reason, unregister the above signal handler again.
 
 =back
 
 
 =back
 

+

 =head1 ANATOMY OF A WATCHER
 
 A watcher is a structure that you create and register to record your
 =head1 ANATOMY OF A WATCHER
 
 A watcher is a structure that you create and register to record your


@@ -578,7 +579,7 @@ programs, though, so beware.
 
 =back
 
 
 =back
 

-=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS
+=head2 GENERIC WATCHER FUNCTIONS

 
 In the following description, C<TYPE> stands for the watcher type,
 e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
 
 In the following description, C<TYPE> stands for the watcher type,
 e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.


@@ -597,7 +598,7 @@ which rolls both calls into one.
 You can reinitialise a watcher at any time as long as it has been stopped
 (or never started) and there are no pending events outstanding.
 
 You can reinitialise a watcher at any time as long as it has been stopped
 (or never started) and there are no pending events outstanding.
 

-The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
+The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,

 int revents)>.
 
 =item C<ev_TYPE_set> (ev_TYPE *, [args])
 int revents)>.
 
 =item C<ev_TYPE_set> (ev_TYPE *, [args])


@@ -693,13 +694,15 @@ This section describes each watcher in detail, but will not repeat
 information given in the last section.
 
 
 information given in the last section.
 
 

-=head2 C<ev_io> - is this file descriptor readable or writable
+=head2 C<ev_io> - is this file descriptor readable or writable?

 
 I/O watchers check whether 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 can stop the watcher if you don't want to
-act on the event and neither want to receive future events).
+in each iteration of the event loop, or, more precisely, when reading
+would not block the process and writing would at least be able to write
+some data. This behaviour is called level-triggering because you keep
+receiving events as long as the 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.

 
 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
 
 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


@@ -709,33 +712,37 @@ 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
 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
+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 C<EVBACKEND_SELECT> and
 C<EVBACKEND_POLL>).
 
 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 C<EVBACKEND_SELECT> and
 C<EVBACKEND_POLL>).
 

+Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness 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
+play around with an Xlib connection), then you have to seperately re-test
+wether a file descriptor is really ready with a known-to-be good interface
+such as poll (fortunately in our Xlib example, Xlib already does this on
+its own, so its quite safe to use).
+

 =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 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.
-
-Please note that most of the more scalable backend mechanisms (for example
-epoll and solaris ports) can result in spurious readyness notifications
-for file descriptors, so you practically need to use non-blocking I/O (and
-treat callback invocation as hint only), or retest separately with a safe
-interface before doing I/O (XLib can do this), or force the use of either
-C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
-problem. Also note that it is quite easy to have your callback invoked
-when the readyness condition is no longer valid even when employing
-typical ways of handling events, so its a good idea to use non-blocking
-I/O unconditionally.
+Configures an C<ev_io> watcher. The C<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
 
 
 =back
 


@@ -758,7 +765,7 @@ attempt to read a whole line in the callback:
   ev_loop (loop, 0);
 
 
   ev_loop (loop, 0);
 
 

-=head2 C<ev_timer> - relative and optionally recurring timeouts
+=head2 C<ev_timer> - relative and optionally repeating timeouts

 
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.
 
 Timer watchers are simple relative timers that generate an event after a
 given time, and optionally repeating in regular intervals after that.


@@ -850,7 +857,7 @@ inactivity.
   ev_timer_again (&mytimer);
 
 
   ev_timer_again (&mytimer);
 
 

-=head2 C<ev_periodic> - to cron or not to cron
+=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).


@@ -988,7 +995,7 @@ Example: call a callback every hour, starting now:
   ev_periodic_start (loop, &hourly_tick);
   
 
   ev_periodic_start (loop, &hourly_tick);
   
 

-=head2 C<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


@@ -1014,7 +1021,7 @@ of the C<SIGxxx> constants).
 =back
 
 
 =back
 
 

-=head2 C<ev_child> - wait for pid status changes
+=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).
 
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).


@@ -1047,7 +1054,7 @@ Example: try to exit cleanly on SIGINT and SIGTERM.
   ev_signal_start (loop, &sigint_cb);
 
 
   ev_signal_start (loop, &sigint_cb);
 
 

-=head2 C<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 events are pending
 (prepare, check and other idle watchers do not count). That is, as long
 
 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


@@ -1091,16 +1098,27 @@ callback, free it. Alos, use no error checking, as usual.
   ev_idle_start (loop, idle_cb);
 
 
   ev_idle_start (loop, idle_cb);
 
 

-=head2 C<ev_prepare> and C<ev_check> - customise your event loop
+=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 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.
 

+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>
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+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
 variable changes, implement your own watchers, integrate net-snmp or a
 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
 variable changes, implement your own watchers, integrate net-snmp or a

-coroutine library and lots more.
+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
 to be watched by the other library, registering C<ev_io> watchers for
 
 This is done by examining in each prepare call which file descriptors need
 to be watched by the other library, registering C<ev_io> watchers for


@@ -1132,10 +1150,63 @@ macros, but using them is utterly, utterly and completely pointless.
 
 =back
 
 
 =back
 

-Example: *TODO*.
+Example: To include a library such as adns, you would add IO watchers
+and a timeout watcher in a prepare handler, as required by libadns, and
+in a check watcher, destroy them and call into libadns. What follows is
+pseudo-code only of course:

 
 

+  static ev_io iow [nfd];
+  static ev_timer tw;
+
+  static void
+  io_cb (ev_loop *loop, ev_io *w, int revents)
+  {
+    // set the relevant poll flags
+    // could also call adns_processreadable etc. here
+    struct pollfd *fd = (struct pollfd *)w->data;
+    if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+    if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+  }

 
 

-=head2 C<ev_embed> - when one backend isn't enough
+  // create io watchers for each fd and a timer before blocking
+  static void
+  adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+  {
+    int timeout = 3600000;truct pollfd fds [nfd];
+    // actual code will need to loop here and realloc etc.
+    adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+    /* the callback is illegal, but won't be called as we stop during check */
+    ev_timer_init (&tw, 0, timeout * 1e-3);
+    ev_timer_start (loop, &tw);
+
+    // create on ev_io per pollfd
+    for (int i = 0; i < nfd; ++i)
+      {
+        ev_io_init (iow + i, io_cb, fds [i].fd,
+          ((fds [i].events & POLLIN ? EV_READ : 0)
+           | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+        fds [i].revents = 0;
+        iow [i].data = fds + i;
+        ev_io_start (loop, iow + i);
+      }
+  }
+
+  // stop all watchers after blocking
+  static void
+  adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+  {
+    ev_timer_stop (loop, &tw);
+
+    for (int i = 0; i < nfd; ++i)
+      ev_io_stop (loop, iow + i);
+
+    adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+  }
+
+
+=head2 C<ev_embed> - when one backend isn't enough...

 
 This is a rather advanced watcher type that lets you embed one event loop
 into another (currently only C<ev_io> events are supported in the embedded
 
 This is a rather advanced watcher type that lets you embed one event loop
 into another (currently only C<ev_io> events are supported in the embedded


@@ -1464,14 +1535,14 @@ in your include path (e.g. in libev/ when using -Ilibev):
 
   ev_win32.c      required on win32 platforms only
 
 
   ev_win32.c      required on win32 platforms only
 

-  ev_select.c     only when select backend is enabled (which is is by default)
+  ev_select.c     only when select backend is enabled (which is by default)

   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
   ev_port.c       only when the solaris port backend is enabled (disabled by default)
 
 F<ev.c> includes the backend files directly when enabled, so you only need
   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
   ev_port.c       only when the solaris port backend is enabled (disabled by default)
 
 F<ev.c> includes the backend files directly when enabled, so you only need

-to compile a single file.
+to compile this single file.

 
 =head3 LIBEVENT COMPATIBILITY API
 
 
 =head3 LIBEVENT COMPATIBILITY API
 


@@ -1494,8 +1565,8 @@ You need the following additional files for this:
 
 Instead of using C<EV_STANDALONE=1> and providing your config in
 whatever way you want, you can also C<m4_include([libev.m4])> in your
 
 Instead of using C<EV_STANDALONE=1> and providing your config in
 whatever way you want, you can also C<m4_include([libev.m4])> in your

-F<configure.ac> and leave C<EV_STANDALONE> off. F<ev.c> will then include
-F<config.h> and configure itself accordingly.
+F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
+include F<config.h> and configure itself accordingly.

 
 For this of course you need the m4 file:
 
 
 For this of course you need the m4 file:
 


@@ -1585,7 +1656,7 @@ backend for BSD and BSD-like systems, although on most BSDs kqueue only
 supports some types of fds correctly (the only platform we found that
 supports ptys for example was NetBSD), so kqueue might be compiled in, but
 not be used unless explicitly requested. The best way to use it is to find
 supports some types of fds correctly (the only platform we found that
 supports ptys for example was NetBSD), so kqueue might be compiled in, but
 not be used unless explicitly requested. The best way to use it is to find

-out wether kqueue supports your type of fd properly and use an embedded
+out whether kqueue supports your type of fd properly and use an embedded

 kqueue loop.
 
 =item EV_USE_PORT
 kqueue loop.
 
 =item EV_USE_PORT


@@ -1631,10 +1702,27 @@ additional independent event loops. Otherwise there will be no support
 for multiple event loops and there is no first event loop pointer
 argument. Instead, all functions act on the single default loop.
 
 for multiple event loops and there is no first event loop pointer
 argument. Instead, all functions act on the single default loop.
 

-=item EV_PERIODICS
+=item EV_PERIODIC_ENABLE
+
+If undefined or defined to be C<1>, then periodic timers are supported. If
+defined to be C<0>, then they are not. Disabling them saves a few kB of
+code.

 
 

-If undefined or defined to be C<1>, then periodic timers are supported,
-otherwise not. This saves a few kb of code.
+=item EV_EMBED_ENABLE
+
+If undefined or defined to be C<1>, then embed watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_STAT_ENABLE
+
+If undefined or defined to be C<1>, then stat watchers are supported. If
+defined to be C<0>, then they are not.
+
+=item EV_MINIMAL
+
+If you need to shave off some kilobytes of code at the expense of some
+speed, define this symbol to C<1>. Currently only used for gcc to override
+some inlining decisions, saves roughly 30% codesize of amd64.

 
 =item EV_COMMON
 
 
 =item EV_COMMON
 


@@ -1649,18 +1737,18 @@ For example, the perl EV module uses something like this:
     SV *self; /* contains this struct */  \
     SV *cb_sv, *fh /* note no trailing ";" */
 
     SV *self; /* contains this struct */  \
     SV *cb_sv, *fh /* note no trailing ";" */
 

-=item EV_CB_DECLARE(type)
+=item EV_CB_DECLARE (type)

 
 

-=item EV_CB_INVOKE(watcher,revents)
+=item EV_CB_INVOKE (watcher, revents)

 
 

-=item ev_set_cb(ev,cb)
+=item ev_set_cb (ev, cb)

 
 Can be used to change the callback member declaration in each watcher,
 and the way callbacks are invoked and set. Must expand to a struct member
 definition and a statement, respectively. See the F<ev.v> header file for
 their default definitions. One possible use for overriding these is to
 
 Can be used to change the callback member declaration in each watcher,
 and the way callbacks are invoked and set. Must expand to a struct member
 definition and a statement, respectively. See the F<ev.v> header file for
 their default definitions. One possible use for overriding these is to

-avoid the ev_loop pointer as first argument in all cases, or to use method
-calls instead of plain function calls in C++.
+avoid the C<struct ev_loop *> as first argument in all cases, or to use
+method calls instead of plain function calls in C++.

 
 =head2 EXAMPLES
 
 
 =head2 EXAMPLES
 


@@ -1675,21 +1763,44 @@ file.
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
 that everybody includes and which overrides some autoconf choices:
 
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
 that everybody includes and which overrides some autoconf choices:
 

-   #define EV_USE_POLL 0
-   #define EV_MULTIPLICITY 0
-   #define EV_PERIODICS 0
-   #define EV_CONFIG_H <config.h>
+  #define EV_USE_POLL 0
+  #define EV_MULTIPLICITY 0
+  #define EV_PERIODICS 0
+  #define EV_CONFIG_H <config.h>

 
 

-   #include "ev++.h"
+  #include "ev++.h"

 
 And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
 
 
 And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
 

-   #include "rxvttoolkit.h"
+  #include "ev_cpp.h"
+  #include "ev.c"
+
+
+=head1 COMPLEXITIES

 
 

-   /* darwin has problems with its header files in C++, requiring this namespace juggling */
-   using namespace ev;
+In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for C<ev_default_init>.
+
+=over 4

 
 

-   #include "ev.c"
+=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
+
+=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+
+=item Starting io/check/prepare/idle/signal/child watchers: O(1)
+
+=item Stopping check/prepare/idle watchers: O(1)
+
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))
+
+=item Finding the next timer per loop iteration: O(1)
+
+=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
+
+=item Activating one watcher: O(1)
+
+=back

 
 
 =head1 AUTHOR
 
 
 =head1 AUTHOR