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

Comparing libev/ev.pod (file contents):
Revision 1.210 by root, Thu Oct 30 08:09:30 2008 UTC vs.
Revision 1.220 by root, Thu Nov 20 11:25:15 2008 UTC

 =head2 EXAMPLE PROGRAM
    // a single header file is required
    #include <ev.h>
+   #include <stdio.h> // for puts
    // every watcher type has its own typedef'd struct
    // with the name ev_TYPE
    ev_io stdin_watcher;
    ev_timer timeout_watcher;
    int
    main (void)
    {
      // use the default event loop unless you have special needs
-     ev_loop *loop = ev_default_loop (0);
+     struct ev_loop *loop = ev_default_loop (0);
      // initialise an io watcher, then start it
      // this one will watch for stdin to become readable
      ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
      ev_io_start (loop, &stdin_watcher);
 i.e. keep at least one watcher active per fd at all times. Stopping and
 starting a watcher (without re-setting it) also usually doesn't cause
 extra overhead. A fork can both result in spurious notifications as well
 as in libev having to destroy and recreate the epoll object, which can
 take considerable time and thus should be avoided.
+All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
+faster than epoll for maybe up to a hundred file descriptors, depending on
+the usage. So sad.
 While nominally embeddable in other event loops, this feature is broken in
 all kernel versions tested so far.
 This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
      else
        {
          // callback was invoked, but there was some activity, re-arm
          // the watcher to fire in last_activity + 60, which is
          // guaranteed to be in the future, so "again" is positive:
-         w->again = timeout - now;
+         w->repeat = timeout - now;
          ev_timer_again (EV_A_ w);
        }
    }
 To summarise the callback: first calculate the real timeout (defined
 C<stat> on that path in regular intervals (or when the OS says it changed)
 and sees if it changed compared to the last time, invoking the callback if
 it did.
 The path does not need to exist: changing from "path exists" to "path does
-not exist" is a status change like any other. The condition "path does
+not exist" is a status change like any other. The condition "path does not
-not exist" is signified by the C<st_nlink> field being zero (which is
+exist" (or more correctly "path cannot be stat'ed") is signified by the
-otherwise always forced to be at least one) and all the other fields of
+C<st_nlink> field being zero (which is otherwise always forced to be at
-the stat buffer having unspecified contents.
+least one) and all the other fields of the stat buffer having unspecified
+contents.
 The path I<must not> end in a slash or contain special components such as
 C<.> or C<..>. The path I<should> be absolute: If it is relative and
 your working directory changes, then the behaviour is undefined.
 This watcher type is not meant for massive numbers of stat watchers,
 as even with OS-supported change notifications, this can be
 resource-intensive.
 At the time of this writing, the only OS-specific interface implemented
-is the Linux inotify interface (implementing kqueue support is left as
+is the Linux inotify interface (implementing kqueue support is left as an
-an exercise for the reader. Note, however, that the author sees no way
+exercise for the reader. Note, however, that the author sees no way of
-of implementing C<ev_stat> semantics with kqueue).
+implementing C<ev_stat> semantics with kqueue, except as a hint).
 =head3 ABI Issues (Largefile Support)
 Libev by default (unless the user overrides this) uses the default
 compilation environment, which means that on systems with large file
 to exchange stat structures with application programs compiled using the
 default compilation environment.
 =head3 Inotify and Kqueue
-When C<inotify (7)> support has been compiled into libev (generally
+When C<inotify (7)> support has been compiled into libev and present at
-only available with Linux 2.6.25 or above due to bugs in earlier
+runtime, it will be used to speed up change detection where possible. The
-implementations) and present at runtime, it will be used to speed up
+inotify descriptor will be created lazily when the first C<ev_stat>
-change detection where possible. The inotify descriptor will be created
+watcher is being started.
-lazily when the first C<ev_stat> watcher is being started.
 Inotify presence does not change the semantics of C<ev_stat> watchers
 except that changes might be detected earlier, and in some cases, to avoid
 making regular C<stat> calls. Even in the presence of inotify support
 there are many cases where libev has to resort to regular C<stat> polling,
-but as long as the path exists, libev usually gets away without polling.
+but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
+many bugs), the path exists (i.e. stat succeeds), and the path resides on
+a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
+xfs are fully working) libev usually gets away without polling.
 There is no support for kqueue, as apparently it cannot be used to
 implement this functionality, due to the requirement of having a file
 descriptor open on the object at all times, and detecting renames, unlinks
 etc. is difficult.
+=head3 C<stat ()> is a synchronous operation
+Libev doesn't normally do any kind of I/O itself, and so is not blocking
+the process. The exception are C<ev_stat> watchers - those call C<stat
+()>, which is a synchronous operation.
+For local paths, this usually doesn't matter: unless the system is very
+busy or the intervals between stat's are large, a stat call will be fast,
+as the path data is suually in memory already (except when starting the
+watcher).
+For networked file systems, calling C<stat ()> can block an indefinite
+time due to network issues, and even under good conditions, a stat call
+often takes multiple milliseconds.
+Therefore, it is best to avoid using C<ev_stat> watchers on networked
+paths, although this is fully supported by libev.
 =head3 The special problem of stat time resolution
 The C<stat ()> system call only supports full-second resolution portably,
 and even on systems where the resolution is higher, most file systems
 Tony Arcieri has written a ruby extension that offers access to a subset
 of the libev API and adds file handle abstractions, asynchronous DNS and
 more on top of it. It can be found via gem servers. Its homepage is at
 L<http://rev.rubyforge.org/>.
+Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
+makes rev work even on mingw.
 =item D
 Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
 be found at L<http://proj.llucax.com.ar/wiki/evd>.
 keeps libev from including F<config.h>, and it also defines dummy
 implementations for some libevent functions (such as logging, which is not
 supported). It will also not define any of the structs usually found in
 F<event.h> that are not directly supported by the libev core alone.
+In stanbdalone mode, libev will still try to automatically deduce the
+configuration, but has to be more conservative.
 =item EV_USE_MONOTONIC
 If defined to be C<1>, libev will try to detect the availability of the
-monotonic clock option at both compile time and runtime. Otherwise no use
+monotonic clock option at both compile time and runtime. Otherwise no
-of the monotonic clock option will be attempted. If you enable this, you
+use of the monotonic clock option will be attempted. If you enable this,
-usually have to link against librt or something similar. Enabling it when
+you usually have to link against librt or something similar. Enabling it
-the functionality isn't available is safe, though, although you have
+when the functionality isn't available is safe, though, although you have
 to make sure you link against any libraries where the C<clock_gettime>
-function is hiding in (often F<-lrt>).
+function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
 =item EV_USE_REALTIME
 If defined to be C<1>, libev will try to detect the availability of the
 real-time clock option at compile time (and assume its availability at
 runtime if successful). Otherwise no use of the real-time clock option will
 be attempted. This effectively replaces C<gettimeofday> by C<clock_get
 (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_CLOCK_SYSCALL
+If defined to be C<1>, libev will try to use a direct syscall instead
+of calling the system-provided C<clock_gettime> function. This option
+exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
+unconditionally pulls in C<libpthread>, slowing down single-threaded
+programs needlessly. Using a direct syscall is slightly slower (in
+theory), because no optimised vdso implementation can be used, but avoids
+the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
+higher, as it simplifies linking (no need for C<-lrt>).
 =item EV_USE_NANOSLEEP
 If defined to be C<1>, libev will assume that C<nanosleep ()> is available
 and will use it for delays. Otherwise it will use C<select ()>.
 =item EV_SELECT_USE_FD_SET
 If defined to C<1>, then the select backend will use the system C<fd_set>
 structure. This is useful if libev doesn't compile due to a missing
-C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
+C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
-exotic systems. This usually limits the range of file descriptors to some
+on exotic systems. This usually limits the range of file descriptors to
-low limit such as 1024 or might have other limitations (winsocket only
+some low limit such as 1024 or might have other limitations (winsocket
-allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
+only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
-influence the size of the C<fd_set> used.
+configures the maximum size of the C<fd_set>.
 =item EV_SELECT_IS_WINSOCKET
 When defined to C<1>, the select backend will assume that
 select/socket/connect etc. don't understand file descriptors but

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Comparing libev/ev.pod (file contents): Revision 1.210 by root, Thu Oct 30 08:09:30 2008 UTC vs. Revision 1.220 by root, Thu Nov 20 11:25:15 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.210 by root, Thu Oct 30 08:09:30 2008 UTC vs.
Revision 1.220 by root, Thu Nov 20 11:25:15 2008 UTC