X-Git-Url: https://git.llucax.com/software/libev.git/blobdiff_plain/480621758fe1687120978562a553920ed46e1b7e..ebc0759db57ff79951aa13a23c97c5846a78a67d:/ev.pod

diff --git a/ev.pod b/ev.pod
index ef9892e..2fd1307 100644
--- a/ev.pod
+++ b/ev.pod
@@ -100,7 +100,9 @@ Libev represents time as a single floating point number, representing the
 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 C<double> type in C, and when you need to do any calculations on
-it, you should treat it as such.
+it, you should treat it as some floatingpoint value. Unlike the name
+component C<stamp> might indicate, it is also used for time differences
+throughout libev.
 
 =head1 GLOBAL FUNCTIONS
 
@@ -119,14 +121,17 @@ you actually want to know.
 
 =item int ev_version_minor ()
 
-You can find out the major and minor version numbers of the library
+You can find out the major and minor ABI version numbers of the library
 you linked against by calling the functions C<ev_version_major> and
 C<ev_version_minor>. If you want, you can compare against the global
 symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
 version of the library your program was compiled against.
 
+These version numbers refer to the ABI version of the library, not the
+release version.
+
 Usually, it's a good idea to terminate if the major versions mismatch,
-as this indicates an incompatible change.  Minor versions are usually
+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.
 
@@ -328,8 +333,8 @@ need to use non-blocking I/O or other means to avoid blocking when no data
 
 Kqueue deserves special mention, as at the time of this writing, it
 was broken on all BSDs except NetBSD (usually it doesn't work with
-anything but sockets and pipes, except on Darwin, where of course its
-completely useless). For this reason its not being "autodetected"
+anything but sockets and pipes, except on Darwin, where of course it's
+completely useless). For this reason it's not being "autodetected"
 unless you explicitly specify it explicitly in the flags (i.e. using
 C<EVBACKEND_KQUEUE>).
 
@@ -401,9 +406,18 @@ etc.). None of the active event watchers will be stopped in the normal
 sense, so e.g. C<ev_is_active> might still return true. It is your
 responsibility to either stop all watchers cleanly yoursef I<before>
 calling this function, or cope with the fact afterwards (which is usually
-the easiest thing, youc na just ignore the watchers and/or C<free ()> them
+the easiest thing, you can just ignore the watchers and/or C<free ()> them
 for example).
 
+Note that certain global state, such as signal state, will not be freed by
+this function, and related watchers (such as signal and child watchers)
+would need to be stopped manually.
+
+In general it is not advisable to call this function except in the
+rare occasion where you really need to free e.g. the signal handling
+pipe fds. If you need dynamically allocated loops it is better to use
+C<ev_loop_new> and C<ev_loop_destroy>).
+
 =item ev_loop_destroy (loop)
 
 Like C<ev_default_destroy>, but destroys an event loop created by an
@@ -488,8 +502,9 @@ 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.
    * If there are no active watchers (reference count is zero), return.
-   - Queue prepare watchers and then call all outstanding watchers.
+   - Queue all prepare watchers and then call all outstanding watchers.
    - If we have been forked, recreate the kernel state.
    - Update the kernel state with all outstanding changes.
    - Update the "event loop time".
@@ -909,6 +924,30 @@ whether 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).
 
+=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,
+such as C<dup>). 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.
+
+To avoid having to explicitly tell libev about such cases, libev follows
+the following policy:  Each time C<ev_io_set> is being called, libev
+will assume that this is potentially a new file descriptor, otherwise
+it is assumed that the file descriptor stays the same. That means that
+you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
+descriptor even if the file descriptor number itself did not change.
+
+This is how one would do it normally anyway, the important point is that
+the libev application should not optimise around libev but should leave
+optimisations to libev.
+
+
+=head3 Watcher-Specific Functions
+
 =over 4
 
 =item ev_io_init (ev_io *, callback, int fd, int events)
@@ -971,6 +1010,8 @@ 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.
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
@@ -1075,16 +1116,18 @@ 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 C<ev_timer>, which would trigger
-roughly 10 seconds later and of course not if you reset your system time
-again).
+roughly 10 seconds later).
 
 They can also be used to implement vastly more complex timers, such as
-triggering an event on eahc midnight, local time.
+triggering an event on each midnight, local time or other, complicated,
+rules.
 
 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.
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
@@ -1096,18 +1139,18 @@ operation, and we will explain them from simplest to complex:
 
 =over 4
 
-=item * absolute timer (interval = reschedule_cb = 0)
+=item * absolute timer (at = time, interval = reschedule_cb = 0)
 
 In this configuration the watcher triggers an event at the wallclock time
 C<at> and doesn't repeat. It 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.
 
-=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)
+=item * non-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) and then repeat, regardless
-of any time jumps.
+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
 time:
@@ -1123,7 +1166,11 @@ Another way to think about it (for the mathematically inclined) is that
 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)
+For numerical stability it is preferable that the C<at> value is near
+C<ev_now ()> (the current time), but there is no range requirement for
+this value.
+
+=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
 
 In this mode the values for C<interval> and C<at> are both being
 ignored. Instead, each time the periodic watcher gets scheduled, the
@@ -1133,7 +1180,7 @@ current time as second argument.
 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).
+starting an C<ev_prepare> watcher, which is legal).
 
 Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
 ev_tstamp now)>, e.g.:
@@ -1166,6 +1213,14 @@ when you changed some parameters or the reschedule callback would return
 a different time than the last time it was called (e.g. in a crond like
 program when the crontabs have changed).
 
+=item ev_tstamp offset [read-write]
+
+When repeating, this contains the offset value, otherwise this is the
+absolute point in time (the C<at> value passed to C<ev_periodic_set>).
+
+Can be modified any time, but changes only take effect when the periodic
+timer fires or C<ev_periodic_again> is being called.
+
 =item ev_tstamp interval [read-write]
 
 The current interval value. Can be modified any time, but changes only
@@ -1178,6 +1233,11 @@ The current reschedule callback, or C<0>, if this functionality is
 switched off. Can be changed any time, but changes only take effect when
 the periodic timer fires or C<ev_periodic_again> is being called.
 
+=item ev_tstamp at [read-only]
+
+When active, contains the absolute time that the watcher is supposed to
+trigger next.
+
 =back
 
 Example: Call a callback every hour, or, more precisely, whenever the
@@ -1228,6 +1288,8 @@ as you don't register any with libev). Similarly, when the last signal
 watcher for a signal is stopped libev will reset the signal handler to
 SIG_DFL (regardless of what it was set to before).
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_signal_init (ev_signal *, callback, int signum)
@@ -1249,6 +1311,8 @@ The signal the watcher watches out for.
 Child watchers trigger when your process receives a SIGCHLD in response to
 some child status changes (most typically when a child of yours dies).
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_child_init (ev_child *, callback, int pid)
@@ -1326,6 +1390,8 @@ 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 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
@@ -1417,6 +1483,8 @@ effect on its own sometimes), idle watchers are a good place to do
 "pseudo-background processing", or delay processing stuff to after the
 event loop has handled all outstanding events.
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_idle_init (ev_signal *, callback)
@@ -1483,6 +1551,18 @@ 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).
 
+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. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
+too) should not activate ("feed") events into libev. While libev fully
+supports this, they will be called before other C<ev_check> watchers did
+their job. As C<ev_check> watchers are often used to embed other event
+loops those other event loops might be in an unusable state until their
+C<ev_check> watcher ran (always remind yourself to coexist peacefully with
+others).
+
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_prepare_init (ev_prepare *, callback)
@@ -1495,10 +1575,18 @@ macros, but using them is utterly, utterly and completely pointless.
 
 =back
 
-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:
+There are a number of principal ways to embed other event loops or modules
+into libev. Here are some ideas on how to include libadns into libev
+(there is a Perl module named C<EV::ADNS> that does this, which you could
+use for an actually working example. Another Perl module named C<EV::Glib>
+embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
+into the Glib event loop).
+
+Method 1: Add IO watchers and a timeout watcher in a prepare handler,
+and in a check watcher, destroy them and call into libadns. What follows
+is pseudo-code only of course. This requires you to either use a low
+priority for the check watcher or use C<ev_clear_pending> explicitly, as
+the callbacks for the IO/timeout watchers might not have been called yet.
 
   static ev_io iow [nfd];
   static ev_timer tw;
@@ -1506,11 +1594,6 @@ pseudo-code only of course:
   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;
   }
 
   // create io watchers for each fd and a timer before blocking
@@ -1526,7 +1609,7 @@ pseudo-code only of course:
     ev_timer_init (&tw, 0, timeout * 1e-3);
     ev_timer_start (loop, &tw);
 
-    // create on ev_io per pollfd
+    // create one ev_io per pollfd
     for (int i = 0; i < nfd; ++i)
       {
         ev_io_init (iow + i, io_cb, fds [i].fd,
@@ -1534,7 +1617,6 @@ pseudo-code only of course:
            | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
 
         fds [i].revents = 0;
-        iow [i].data = fds + i;
         ev_io_start (loop, iow + i);
       }
   }
@@ -1546,11 +1628,80 @@ pseudo-code only of course:
     ev_timer_stop (loop, &tw);
 
     for (int i = 0; i < nfd; ++i)
-      ev_io_stop (loop, iow + i);
+      {
+        // set the relevant poll flags
+        // could also call adns_processreadable etc. here
+        struct pollfd *fd = fds + i;
+        int revents = ev_clear_pending (iow + i);
+        if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+        if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+
+        // now stop the watcher
+        ev_io_stop (loop, iow + i);
+      }
 
     adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
   }
 
+Method 2: This would be just like method 1, but you run C<adns_afterpoll>
+in the prepare watcher and would dispose of the check watcher.
+
+Method 3: If the module to be embedded supports explicit event
+notification (adns does), you can also make use of the actual watcher
+callbacks, and only destroy/create the watchers in the prepare watcher.
+
+  static void
+  timer_cb (EV_P_ ev_timer *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    adns_processtimeouts (ads, &tv_now);
+  }
+
+  static void
+  io_cb (EV_P_ ev_io *w, int revents)
+  {
+    adns_state ads = (adns_state)w->data;
+    update_now (EV_A);
+
+    if (revents & EV_READ ) adns_processreadable  (ads, w->fd, &tv_now);
+    if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
+  }
+
+  // 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, youc na override
+their poll function.  The drawback with this solution is that the main
+loop is now no longer controllable by EV. The C<Glib::EV> module does
+this.
+
+  static gint
+  event_poll_func (GPollFD *fds, guint nfds, gint timeout)
+  {
+    int got_events = 0;
+
+    for (n = 0; n < nfds; ++n)
+      // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
+
+    if (timeout >= 0)
+      // create/start timer
+
+    // poll
+    ev_loop (EV_A_ 0);
+
+    // stop timer again
+    if (timeout >= 0)
+      ev_timer_stop (EV_A_ &to);
+
+    // stop io watchers again - their callbacks should have set
+    for (n = 0; n < nfds; ++n)
+      ev_io_stop (EV_A_ iow [n]);
+
+    return got_events;
+  }
+
 
 =head2 C<ev_embed> - when one backend isn't enough...
 
@@ -1622,6 +1773,8 @@ create it, and if that fails, use the normal loop for everything:
   else
     loop_lo = loop_hi;
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
@@ -1640,7 +1793,7 @@ Make a single, non-blocking sweep over the embedded loop. This works
 similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
 apropriate way for embedded loops.
 
-=item struct ev_loop *loop [read-only]
+=item struct ev_loop *other [read-only]
 
 The embedded event loop.
 
@@ -1657,6 +1810,8 @@ and only in the child after the fork. If whoever good citizen calling
 C<ev_default_fork> cheats and calls it in the wrong process, the fork
 handlers will be invoked, too, of course.
 
+=head3 Watcher-Specific Functions and Data Members
+
 =over 4
 
 =item ev_fork_init (ev_signal *, callback)
@@ -1846,14 +2001,21 @@ Example: simple class declaration and watcher initialisation
   ev::io iow;
   iow.set <myclass, &myclass::io_cb> (&obj);
 
-=item w->set (void (*function)(watcher &w, int), void *data = 0)
+=item w->set<function> (void *data = 0)
 
 Also sets a callback, but uses a static method or plain function as
 callback. The optional C<data> argument will be stored in the watcher's
 C<data> member and is free for you to use.
 
+The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
+
 See the method-C<set> above for more details.
 
+Example:
+
+  static void io_cb (ev::io &w, int revents) { }
+  iow.set <io_cb> ();
+
 =item w->set (struct ev_loop *)
 
 Associates a different C<struct ev_loop> with this watcher. You can only
@@ -1875,16 +2037,16 @@ constructor already stores the event loop.
 
 Stops the watcher if it is active. Again, no C<loop> argument.
 
-=item w->again ()       C<ev::timer>, C<ev::periodic> only
+=item w->again () (C<ev::timer>, C<ev::periodic> only)
 
 For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
 C<ev_TYPE_again> function.
 
-=item w->sweep ()       C<ev::embed> only
+=item w->sweep () (C<ev::embed> only)
 
 Invokes C<ev_embed_sweep>.
 
-=item w->update ()      C<ev::stat> only
+=item w->update () (C<ev::stat> only)
 
 Invokes C<ev_stat_stat>.
 
@@ -1914,9 +2076,9 @@ the constructor.
 
 =head1 MACRO MAGIC
 
-Libev can be compiled with a variety of options, the most fundemantal is
-C<EV_MULTIPLICITY>. This option determines whether (most) functions and
-callbacks have an initial C<struct ev_loop *> argument.
+Libev can be compiled with a variety of options, the most fundamantal
+of which is C<EV_MULTIPLICITY>. This option determines whether (most)
+functions and callbacks have an initial C<struct ev_loop *> argument.
 
 To make it easier to write programs that cope with either variant, the
 following macros are defined:
@@ -1980,7 +2142,7 @@ applications. Examples of applications that embed it include the Deliantra
 Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
 and rxvt-unicode.
 
-The goal is to enable you to just copy the neecssary files into your
+The goal is to enable you to just copy the necessary files into your
 source directory without having to change even a single line in them, so
 you can easily upgrade by simply copying (or having a checked-out copy of
 libev somewhere in your source tree).
@@ -2090,8 +2252,8 @@ If defined to be C<1>, libev will try to detect the availability of the
 realtime clock option at compiletime (and assume its availability at
 runtime if successful). Otherwise no use of the realtime clock option will
 be attempted. This effectively replaces C<gettimeofday> by C<clock_get
-(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
-in the description of C<EV_USE_MONOTONIC>, though.
+(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
+note about libraries in the description of C<EV_USE_MONOTONIC>, though.
 
 =item EV_USE_SELECT
 
@@ -2285,6 +2447,31 @@ their default definitions. One possible use for overriding these is to
 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 EXPORTED API SYMBOLS
+
+If you need to re-export the API (e.g. via a dll) and you need a list of
+exported symbols, you can use the provided F<Symbol.*> files which list
+all public symbols, one per line:
+
+  Symbols.ev      for libev proper
+  Symbols.event   for the libevent emulation
+
+This can also be used to rename all public symbols to avoid clashes with
+multiple versions of libev linked together (which is obviously bad in
+itself, but sometimes it is inconvinient to avoid this).
+
+A sed comamnd like this will create wrapper C<#define>'s that you need to
+include before including F<ev.h>:
+
+   <Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
+
+This would create a file F<wrap.h> which essentially looks like this:
+
+   #define ev_backend     myprefix_ev_backend
+   #define ev_check_start myprefix_ev_check_start
+   #define ev_check_stop  myprefix_ev_check_stop
+   ...
+
 =head2 EXAMPLES
 
 For a real-world example of a program the includes libev