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

Comparing libev/ev.pod (file contents):
Revision 1.111 by root, Tue Dec 25 18:01:20 2007 UTC vs.
Revision 1.117 by root, Wed Jan 9 04:15:39 2008 UTC

 While this backend scales well, it requires one system call per active
 file descriptor per loop iteration. For small and medium numbers of file
 descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
 might perform better.
+On the positive side, ignoring the spurious readyness notifications, this
+backend actually performed to specification in all tests and is fully
+embeddable, which is a rare feat among the OS-specific backends.
 =item C<EVBACKEND_ALL>
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
 It is definitely not recommended to use this flag.
 =back
 If one or more of these are ored into the flags value, then only these
-backends will be tried (in the reverse order as given here). If none are
+backends will be tried (in the reverse order as listed here). If none are
-specified, most compiled-in backend will be tried, usually in reverse
+specified, all backends in C<ev_recommended_backends ()> will be tried.
-order of their flag values :)
 The most typical usage is like this:
   if (!ev_default_loop (0))
     fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
 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.
+   * If EVFLAG_FORKCHECK was used, check for a fork.
-   - Queue all prepare watchers and then call all outstanding watchers.
+   - If a fork was detected, queue and call all fork watchers.
+   - Queue and call all prepare watchers.
    - If we have been forked, recreate the kernel state.
    - Update the kernel state with all outstanding changes.
    - Update the "event loop time".
-   - Calculate for how long to block.
+   - Calculate for how long to sleep or block, if at all
+     (active idle watchers, EVLOOP_NONBLOCK or not having
+     any active watchers at all will result in not sleeping).
+   - Sleep if the I/O and timer collect interval say so.
    - Block the process, waiting for any events.
    - Queue all outstanding I/O (fd) events.
    - Update the "event loop time" and do time jump handling.
    - Queue all outstanding timers.
    - Queue all outstanding periodics.
    - If no events are pending now, queue all idle watchers.
    - Queue all check watchers.
    - Call all queued watchers in reverse order (i.e. check watchers first).
      Signals and child watchers are implemented as I/O watchers, and will
      be handled here by queueing them when their watcher gets executed.
-   - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+   - If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
-     were used, return, otherwise continue with step *.
+     were used, or there are no active watchers, return, otherwise
+     continue with step *.
-Example: Queue some jobs and then loop until no events are outsanding
+Example: Queue some jobs and then loop until no events are outstanding
 anymore.
    ... queue jobs here, make sure they register event watchers as long
    ... as they still have work to do (even an idle watcher will do..)
    ev_loop (my_loop, 0);
 Can be used to make a call to C<ev_loop> return early (but only after it
 has processed all outstanding events). The C<how> argument must be either
 C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
 C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
+This "unloop state" will be cleared when entering C<ev_loop> again.
 =item ev_ref (loop)
 =item ev_unref (loop)
 returning, ev_unref() after starting, and ev_ref() before stopping it. For
 example, libev itself uses this for its internal signal pipe: It is not
 visible to the libev user and should not keep C<ev_loop> from exiting if
 no event watchers registered by it are active. It is also an excellent
 way to do this for generic recurring timers or from within third-party
-libraries. Just remember to I<unref after start> and I<ref before stop>.
+libraries. Just remember to I<unref after start> and I<ref before stop>
+(but only if the watcher wasn't active before, or was active before,
+respectively).
 Example: Create a signal watcher, but keep it from keeping C<ev_loop>
 running when nothing else is active.
   struct ev_signal exitsig;
 be used is the winsock select). This means that it will call
 C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
 it is assumed that all these functions actually work on fds, even
 on win32. Should not be defined on non-win32 platforms.
+=item EV_FD_TO_WIN32_HANDLE
+If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
+file descriptors to socket handles. When not defining this symbol (the
+default), then libev will call C<_get_osfhandle>, which is usually
+correct. In some cases, programs use their own file descriptor management,
+in which case they can provide this function to map fds to socket handles.
 =item EV_USE_POLL
 If defined to be C<1>, libev will compile in support for the C<poll>(2)
 backend. Otherwise it will be enabled on non-win32 platforms. It
 takes precedence over select.
 watchers becomes O(1) w.r.t. prioritiy handling.
 =back
+=head1 Win32 platform limitations and workarounds
+Win32 doesn't support any of the standards (e.g. POSIX) that libev
+requires, and its I/O model is fundamentally incompatible with the POSIX
+model. Libev still offers limited functionality on this platform in
+the form of the C<EVBACKEND_SELECT> backend, and only supports socket
+descriptors. This only applies when using Win32 natively, not when using
+e.g. cygwin.
+There is no supported compilation method available on windows except
+embedding it into other applications.
+Due to the many, low, and arbitrary limits on the win32 platform and the
+abysmal performance of winsockets, using a large number of sockets is not
+recommended (and not reasonable). If your program needs to use more than
+a hundred or so sockets, then likely it needs to use a totally different
+implementation for windows, as libev offers the POSIX model, which cannot
+be implemented efficiently on windows (microsoft monopoly games).
+=over 4
+=item The winsocket select function
+The winsocket C<select> function doesn't follow POSIX in that it requires
+socket I<handles> and not socket I<file descriptors>. This makes select
+very inefficient, and also requires a mapping from file descriptors
+to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
+C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
+symbols for more info.
+The configuration for a "naked" win32 using the microsoft runtime
+libraries and raw winsocket select is:
+  #define EV_USE_SELECT 1
+  #define EV_SELECT_IS_WINSOCKET 1   /* forces EV_SELECT_USE_FD_SET, too */
+Note that winsockets handling of fd sets is O(n), so you can easily get a
+complexity in the O(n²) range when using win32.
+=item Limited number of file descriptors
+Windows has numerous arbitrary (and low) limits on things. Early versions
+of winsocket's select only supported waiting for a max. of C<64> handles
+(probably owning to the fact that all windows kernels can only wait for
+C<64> things at the same time internally; microsoft recommends spawning a
+chain of threads and wait for 63 handles and the previous thread in each).
+Newer versions support more handles, but you need to define C<FD_SETSIZE>
+to some high number (e.g. C<2048>) before compiling the winsocket select
+call (which might be in libev or elsewhere, for example, perl does its own
+select emulation on windows).
+Another limit is the number of file descriptors in the microsoft runtime
+libraries, which by default is C<64> (there must be a hidden I<64> fetish
+or something like this inside microsoft). You can increase this by calling
+C<_setmaxstdio>, which can increase this limit to C<2048> (another
+arbitrary limit), but is broken in many versions of the microsoft runtime
+libraries.
+This might get you to about C<512> or C<2048> sockets (depending on
+windows version and/or the phase of the moon). To get more, you need to
+wrap all I/O functions and provide your own fd management, but the cost of
+calling select (O(n²)) will likely make this unworkable.
+=back
 =head1 AUTHOR
 Marc Lehmann <libev@schmorp.de>.

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Comparing libev/ev.pod (file contents): Revision 1.111 by root, Tue Dec 25 18:01:20 2007 UTC vs. Revision 1.117 by root, Wed Jan 9 04:15:39 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.111 by root, Tue Dec 25 18:01:20 2007 UTC vs.
Revision 1.117 by root, Wed Jan 9 04:15:39 2008 UTC