avoid backend_modify call unless ev_io_set was used

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 3ad52c033150467c481e7a211df16825726e238d..ab57ffbd559a2819c7d245ec80c9900ebb82d558 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -119,14 +119,17 @@ you actually want to know.
 
 =item int ev_version_minor ()
 
 
 =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.
 
 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,
 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.
 
 compatible to older versions, so a larger minor version alone is usually
 not a problem.
 


@@ -910,6 +913,28 @@ 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).
 
 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.
+
+

 =over 4
 
 =item ev_io_init (ev_io *, callback, int fd, int events)
 =over 4
 
 =item ev_io_init (ev_io *, callback, int fd, int events)