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

Comparing libev/ev.pod (file contents):
Revision 1.322 by root, Sun Oct 24 17:58:41 2010 UTC vs.
Revision 1.339 by root, Sun Oct 31 22:19:38 2010 UTC

 on event-based programming, nor will it introduce event-based programming
 with libev.
 Familiarity with event based programming techniques in general is assumed
 throughout this document.
+=head1 WHAT TO READ WHEN IN A HURRY
+This manual tries to be very detailed, but unfortunately, this also makes
+it very long. If you just want to know the basics of libev, I suggest
+reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
+look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
+C<ev_timer> sections in L<WATCHER TYPES>.
 =head1 ABOUT LIBEV
 Libev is an event loop: you register interest in certain events (such as a
 file descriptor being readable or a timeout occurring), and it will manage
 the current system, you would need to look at C<ev_embeddable_backends ()
 & ev_supported_backends ()>, likewise for recommended ones.
 See the description of C<ev_embed> watchers for more info.
-=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
+=item ev_set_allocator (void *(*cb)(void *ptr, long size))
 Sets the allocation function to use (the prototype is similar - the
 semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
 used to allocate and free memory (no surprises here). If it returns zero
 when memory needs to be allocated (C<size != 0>), the library might abort
    }
    ...
    ev_set_allocator (persistent_realloc);
-=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
+=item ev_set_syserr_cb (void (*cb)(const char *msg))
 Set the callback function to call on a retryable system call 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 situation, no
 An event loop is described by a C<struct ev_loop *> (the C<struct> is
 I<not> optional in this case unless libev 3 compatibility is disabled, as
 libev 3 had an C<ev_loop> function colliding with the struct name).
 The library knows two types of such loops, the I<default> loop, which
-supports signals and child events, and dynamically created event loops
+supports child process events, and dynamically created event loops which
-which do not.
+do not.
 =over 4
 =item struct ev_loop *ev_default_loop (unsigned int flags)
 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);
-Example: Use whatever libev has to offer, but make sure that kqueue is
-used if available (warning, breaks stuff, best use only with your own
-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)
 This will create and initialise a new event loop object. If the loop
 could not be initialised, returns false.
 epoll scales either O(1) or O(active_fds).
 The epoll mechanism deserves honorable mention as the most misdesigned
 of the more advanced event mechanisms: mere annoyances include silently
 dropping file descriptors, requiring a system call per change per file
-descriptor (and unnecessary guessing of parameters), problems with dup and
+descriptor (and unnecessary guessing of parameters), problems with dup,
+returning before the timeout value, resulting in additional iterations
+(and only giving 5ms accuracy while select on the same platform gives
-so on. The biggest issue is fork races, however - if a program forks then
+0.1ms) and so on. The biggest issue is fork races, however - if a program
-I<both> parent and child process have to recreate the epoll set, which can
+forks then I<both> parent and child process have to recreate the epoll
-take considerable time (one syscall per file descriptor) and is of course
+set, which can take considerable time (one syscall per file descriptor)
-hard to detect.
+and is of course hard to detect.
 Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
 of course I<doesn't>, and epoll just loves to report events for totally
 I<different> file descriptors (even already closed ones, so one cannot
 even remove them from the set) than registered in the set (especially
 employing an additional generation counter and comparing that against the
 events to filter out spurious ones, recreating the set when required. Last
 not least, it also refuses to work with some file descriptors which work
 perfectly fine with C<select> (files, many character devices...).
+Epoll is truly the train wreck analog among event poll mechanisms.
 While stopping, setting and starting an I/O watcher in the same iteration
 will result in some caching, there is still a system call per such
 incident (because the same I<file descriptor> could point to a different
 I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
 file descriptors might not work very well if you register events for both
 Example: Try to create a event loop that uses epoll and nothing else.
    struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
    if (!epoller)
      fatal ("no epoll found here, maybe it hides under your chair");
+Example: Use whatever libev has to offer, but make sure that kqueue is
+used if available.
+   struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
 =item ev_loop_destroy (loop)
 Destroys an event loop object (frees all memory and kernel state
 etc.). None of the active event watchers will be stopped in the normal
 Can be used to make a call to C<ev_run> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
 C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
-This "unloop state" will be cleared when entering C<ev_run> again.
+This "break state" will be cleared when entering C<ev_run> again.
-It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
+It is safe to call C<ev_break> from outside any C<ev_run> calls, too.
 =item ev_ref (loop)
 =item ev_unref (loop)
 =item C<EV_FORK>
 The event loop has been resumed in the child process after fork (see
 C<ev_fork>).
+=item C<EV_CLEANUP>
+The event loop is about to be destroyed (see C<ev_cleanup>).
 =item C<EV_ASYNC>
 The given async watcher has been asynchronously notified (see C<ev_async>).
 =item C<EV_CUSTOM>
 programs, though, as the fd could already be closed and reused for another
 thing, so beware.
 =back
-=head2 WATCHER STATES
-There are various watcher states mentioned throughout this manual -
-active, pending and so on. In this section these states and the rules to
-transition between them will be described in more detail - and while these
-rules might look complicated, they usually do "the right thing".
-=over 4
-=item initialiased
-Before a watcher can be registered with the event looop it has to be
-initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
-C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
-In this state it is simply some block of memory that is suitable for use
-in an event loop. It can be moved around, freed, reused etc. at will.
-=item started/running/active
-Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
-property of the event loop, and is actively waiting for events. While in
-this state it cannot be accessed (except in a few documented ways), moved,
-freed or anything else - the only legal thing is to keep a pointer to it,
-and call libev functions on it that are documented to work on active watchers.
-=item pending
-If a watcher is active and libev determines that an event it is interested
-in has occurred (such as a timer expiring), it will become pending. It will
-stay in this pending state until either it is stopped or its callback is
-about to be invoked, so it is not normally pending inside the watcher
-callback.
-The watcher might or might not be active while it is pending (for example,
-an expired non-repeating timer can be pending but no longer active). If it
-is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
-but it is still property of the event loop at this time, so cannot be
-moved, freed or reused. And if it is active the rules described in the
-previous item still apply.
-It is also possible to feed an event on a watcher that is not active (e.g.
-via C<ev_feed_event>), in which case it becomes pending without being
-active.
-=item stopped
-A watcher can be stopped implicitly by libev (in which case it might still
-be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
-latter will clear any pending state the watcher might be in, regardless
-of whether it was active or not, so stopping a watcher explicitly before
-freeing it is often a good idea.
-While stopped (and not pending) the watcher is essentially in the
-initialised state, that is it can be reused, moved, modified in any way
-you wish.
-=back
 =head2 GENERIC WATCHER FUNCTIONS
 =over 4
 =item C<ev_init> (ev_TYPE *watcher, callback)
 See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
 functions that do not need a watcher.
 =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
    t2_cb (EV_P_ ev_timer *w, int revents)
    {
      struct my_biggy big = (struct my_biggy *)
        (((char *)w) - offsetof (struct my_biggy, t2));
    }
+=head2 WATCHER STATES
+There are various watcher states mentioned throughout this manual -
+active, pending and so on. In this section these states and the rules to
+transition between them will be described in more detail - and while these
+rules might look complicated, they usually do "the right thing".
+=over 4
+=item initialiased
+Before a watcher can be registered with the event looop it has to be
+initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
+C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
+In this state it is simply some block of memory that is suitable for use
+in an event loop. It can be moved around, freed, reused etc. at will.
+=item started/running/active
+Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
+property of the event loop, and is actively waiting for events. While in
+this state it cannot be accessed (except in a few documented ways), moved,
+freed or anything else - the only legal thing is to keep a pointer to it,
+and call libev functions on it that are documented to work on active watchers.
+=item pending
+If a watcher is active and libev determines that an event it is interested
+in has occurred (such as a timer expiring), it will become pending. It will
+stay in this pending state until either it is stopped or its callback is
+about to be invoked, so it is not normally pending inside the watcher
+callback.
+The watcher might or might not be active while it is pending (for example,
+an expired non-repeating timer can be pending but no longer active). If it
+is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
+but it is still property of the event loop at this time, so cannot be
+moved, freed or reused. And if it is active the rules described in the
+previous item still apply.
+It is also possible to feed an event on a watcher that is not active (e.g.
+via C<ev_feed_event>), in which case it becomes pending without being
+active.
+=item stopped
+A watcher can be stopped implicitly by libev (in which case it might still
+be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
+latter will clear any pending state the watcher might be in, regardless
+of whether it was active or not, so stopping a watcher explicitly before
+freeing it is often a good idea.
+While stopped (and not pending) the watcher is essentially in the
+initialised state, that is it can be reused, moved, modified in any way
+you wish.
+=back
 =head2 WATCHER PRIORITY MODELS
 Many event loops support I<watcher priorities>, which are usually small
 integers that influence the ordering of event callback invocation
 =head3 Watcher-Specific Functions and Data Members
 =over 4
-=item ev_fork_init (ev_signal *, callback)
+=item ev_fork_init (ev_fork *, callback)
 Initialises and configures the fork watcher - it has no parameters of any
 kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
-believe me.
+really.
 =back
+=head2 C<ev_cleanup> - even the best things end
+Cleanup watchers are called just before the event loop is being destroyed
+by a call to C<ev_loop_destroy>.
+While there is no guarantee that the event loop gets destroyed, cleanup
+watchers provide a convenient method to install cleanup hooks for your
+program, worker threads and so on - you just to make sure to destroy the
+loop when you want them to be invoked.
+Cleanup watchers are invoked in the same way as any other watcher. Unlike
+all other watchers, they do not keep a reference to the event loop (which
+makes a lot of sense if you think about it). Like all other watchers, you
+can call libev functions in the callback, except C<ev_cleanup_start>.
+=head3 Watcher-Specific Functions and Data Members
+=over 4
+=item ev_cleanup_init (ev_cleanup *, callback)
+Initialises and configures the cleanup watcher - it has no parameters of
+any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
+pointless, I assure you.
+=back
+Example: Register an atexit handler to destroy the default loop, so any
+cleanup functions are called.
+   static void
+   program_exits (void)
+   {
+     ev_loop_destroy (EV_DEFAULT_UC);
+   }
+   ...
+   atexit (program_exits);
 =head2 C<ev_async> - how to wake up an event loop
 In general, you cannot use an C<ev_run> from multiple threads or other
 structure (guaranteed by POSIX but not by ISO C for example), but it also
 assumes that the same (machine) code can be used to call any watcher
 callback: The watcher callbacks have different type signatures, but libev
 calls them using an C<ev_watcher *> internally.
+=item pointer accesses must be thread-atomic
+Accessing a pointer value must be atomic, it must both be readable and
+writable in one piece - this is the case on all current architectures.
 =item C<sig_atomic_t volatile> must be thread-atomic as well
 The type C<sig_atomic_t volatile> (or whatever is defined as
 C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
 threads. This is not part of the specification for C<sig_atomic_t>, but is
 =back
 =head1 PORTING FROM LIBEV 3.X TO 4.X
-The major version 4 introduced some minor incompatible changes to the API.
+The major version 4 introduced some incompatible changes to the API.
-At the moment, the C<ev.h> header file tries to implement superficial
+At the moment, the C<ev.h> header file provides compatibility definitions
-compatibility, so most programs should still compile. Those might be
+for all changes, so most programs should still compile. The compatibility
-removed in later versions of libev, so better update early than late.
+layer might be removed in later versions of libev, so better update to the
+new API early than late.
 =over 4
+=item C<EV_COMPAT3> backwards compatibility mechanism
+The backward compatibility mechanism can be controlled by
+C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
+section.
 =item C<ev_default_destroy> and C<ev_default_fork> have been removed
 These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
-   ev_loop_destroy (EV_DEFAULT);
+   ev_loop_destroy (EV_DEFAULT_UC);
    ev_loop_fork (EV_DEFAULT);
 =item function/symbol renames
 A number of functions and symbols have been renamed:
 ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
 as all other watcher types. Note that C<ev_loop_fork> is still called
 C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
 typedef.
-=item C<EV_COMPAT3> backwards compatibility mechanism
-The backward compatibility mechanism can be controlled by
-C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
-section.
 =item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
 The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
 mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
 and work, but the library code will of course be larger.
 =back
 =head1 AUTHOR
-Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
+Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
+Magnusson and Emanuele Giaquinta.

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Comparing libev/ev.pod (file contents): Revision 1.322 by root, Sun Oct 24 17:58:41 2010 UTC vs. Revision 1.339 by root, Sun Oct 31 22:19:38 2010 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.322 by root, Sun Oct 24 17:58:41 2010 UTC vs.
Revision 1.339 by root, Sun Oct 31 22:19:38 2010 UTC