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

Comparing libev/ev.pod (file contents):
Revision 1.431 by root, Fri Nov 22 16:42:10 2013 UTC vs.
Revision 1.443 by root, Thu Aug 30 21:51:15 2018 UTC

 make libev check for a fork in each iteration by enabling this flag.
 This works by calling C<getpid ()> on every iteration of the loop,
 and thus this might slow down your event loop if you do a lot of loop
 iterations and little real work, but is usually not noticeable (on my
-GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
+GNU/Linux system for example, C<getpid> is actually a simple 5-insn
-without a system call and thus I<very> fast, but my GNU/Linux system also has
+sequence without a system call and thus I<very> fast, but my GNU/Linux
-C<pthread_atfork> which is even faster).
+system also has C<pthread_atfork> which is even faster). (Update: glibc
+versions 2.25 apparently removed the C<getpid> optimisation again).
 The big advantage of this flag is that you can forget about fork (and
-forget about forgetting to tell libev about forking) when you use this
+forget about forgetting to tell libev about forking, although you still
-flag.
+have to ignore C<SIGPIPE>) when you use this flag.
 This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
 environment variable.
 =item C<EVFLAG_NOINOTIFY>
 If you need dynamically allocated loops it is better to use C<ev_loop_new>
 and C<ev_loop_destroy>.
 =item ev_loop_fork (loop)
-This function sets a flag that causes subsequent C<ev_run> iterations to
+This function sets a flag that causes subsequent C<ev_run> iterations
-reinitialise the kernel state for backends that have one. Despite the
+to reinitialise the kernel state for backends that have one. Despite
-name, you can call it anytime, but it makes most sense after forking, in
+the name, you can call it anytime you are allowed to start or stop
-the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
+watchers (except inside an C<ev_prepare> callback), but it makes most
+sense after forking, in the child process. You I<must> call it (or use
-child before resuming or calling C<ev_run>.
+C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
+In addition, if you want to reuse a loop (via this function or
+C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
 Again, you I<have> to call it on I<any> loop that you want to re-use after
 a fork, I<even if you do not plan to use the loop in the parent>. This is
 because some kernel interfaces *cough* I<kqueue> *cough* do funny things
 during fork.
 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:
+timeout on the current time, use something like the following to adjust
+for it:
-   ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
+   ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
 If the event loop is suspended for a long time, you can also force an
 update of the time returned by C<ev_now ()> by calling C<ev_now_update
-()>.
+()>, although that will push the event time of all outstanding events
+further into the future.
 =head3 The special problem of unsynchronised clocks
 Modern systems have a variety of clocks - libev itself uses the normal
 "wall clock" clock and, if available, the monotonic clock (to avoid time
 =item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
 =item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
-Configure the timer to trigger after C<after> seconds. If C<repeat>
+Configure the timer to trigger after C<after> seconds (fractional and
-is C<0.>, then it will automatically be stopped once the timeout is
+negative values are supported). If C<repeat> is C<0.>, then it will
-reached. If it is positive, then the timer will automatically be
+automatically be stopped once the timeout is reached. If it is positive,
-configured to trigger again C<repeat> seconds later, again, and again,
+then the timer will automatically be configured to trigger again C<repeat>
-until stopped manually.
+seconds 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 normally
 trigger at exactly 10 second intervals. If, however, your program cannot
 keep up with the timer (because it takes longer than those 10 seconds to
 Periodic watchers are also timers of a kind, but they are very versatile
 (and unfortunately a bit complex).
 Unlike C<ev_timer>, periodic watchers are not based on real time (or
 relative time, the physical time that passes) but on wall clock time
-(absolute time, the thing you can read on your calender or clock). The
+(absolute time, the thing you can read on your calendar or clock). The
 difference is that wall clock time can run faster or slower than real
 time, and time jumps are not uncommon (e.g. when you adjust your
 wrist-watch).
 You can tell a periodic watcher to trigger after some specific point
    ev_periodic hourly_tick;
    ev_periodic_init (&hourly_tick, clock_cb,
                      fmod (ev_now (loop), 3600.), 3600., 0);
    ev_periodic_start (loop, &hourly_tick);
 =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
 Prepare and check watchers are often (but not always) used in pairs:
 prepare watchers get invoked before the process blocks and check watchers
 afterwards.
-You I<must not> call C<ev_run> or similar functions that enter
+You I<must not> call C<ev_run> (or similar functions that enter the
-the current event loop from either C<ev_prepare> or C<ev_check>
+current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
-watchers. Other loops than the current one are fine, however. The
+C<ev_check> watchers. Other loops than the current one are fine,
-rationale behind this is that you do not need to check for recursion in
+however. The rationale behind this is that you do not need to check
-those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
+for recursion in those watchers, i.e. the sequence will always be
-C<ev_check> so if you have one watcher of each kind they will always be
+C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
-called in pairs bracketing the blocking call.
+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. They could be used, for example, to track
 variable changes, implement your own watchers, integrate net-snmp or a
 coroutine library and lots more. They are also occasionally useful if
 used).
    struct ev_loop *loop_hi = ev_default_init (0);
    struct ev_loop *loop_lo = 0;
    ev_embed embed;
    // see if there is a chance of getting one that works
    // (remember that a flags value of 0 means autodetection)
    loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
      ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
      : 0;
 C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
    struct ev_loop *loop = ev_default_init (0);
    struct ev_loop *loop_socket = 0;
    ev_embed embed;
    if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
      if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
        {
          ev_embed_init (&embed, 0, loop_socket);
          ev_embed_start (loop, &embed);
 and calls it in the wrong process, the fork handlers will be invoked, too,
 of course.
 =head3 The special problem of life after fork - how is it possible?
-Most uses of C<fork()> consist of forking, then some simple calls to set
+Most uses of C<fork ()> consist of forking, then some simple calls to set
 up/change the process environment, followed by a call to C<exec()>. This
 sequence should be handled by libev without any problems.
 This changes when the application actually wants to do event handling
 in the child, or both parent in child, in effect "continuing" after the
 There are some other functions of possible interest. Described. Here. Now.
 =over 4
-=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
+=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
 This function combines a simple timer and an I/O watcher, calls your
 callback on whichever event happens first and automatically stops both
 watchers. This is useful if you want to wait for a single event on an fd
 or timeout without having to allocate/configure/start/stop/free one or
 To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
 files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
    // my_ev.h
    #define EV_CB_DECLARE(type)   struct my_coro *cb;
-   #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
+   #define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
    #include "../libev/ev.h"
    // my_ev.c
    #define EV_H "my_ev.h"
    #include "../libev/ev.c"
      void operator() (ev::io &w, int revents)
      {
        ...
      }
    }
    myfunctor f;
    ev::io w;
    w.set (&f);
    ev_vars.h
    ev_wrap.h
    ev_win32.c      required on win32 platforms only
-   ev_select.c     only when select backend is enabled (which is enabled by default)
+   ev_select.c     only when select backend is enabled
-   ev_poll.c       only when poll backend is enabled (disabled by default)
+   ev_poll.c       only when poll backend is enabled
-   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
+   ev_epoll.c      only when the epoll backend is enabled
-   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
+   ev_kqueue.c     only when the kqueue backend is enabled
-   ev_port.c       only when the solaris port backend is enabled (disabled by default)
+   ev_port.c       only when the solaris port backend is enabled
 F<ev.c> includes the backend files directly when enabled, so you only need
 to compile this single file.
 =head3 LIBEVENT COMPATIBILITY API
 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 null pointers and integer zero are represented by 0 bytes
+Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
+relies on this setting pointers and integers to null.
 =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.

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libev/ev.pod (file contents): Revision 1.431 by root, Fri Nov 22 16:42:10 2013 UTC vs. Revision 1.443 by root, Thu Aug 30 21:51:15 2018 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.431 by root, Fri Nov 22 16:42:10 2013 UTC vs.
Revision 1.443 by root, Thu Aug 30 21:51:15 2018 UTC