-.\" $Id$
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+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
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.TH curl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_fdset - extracts file descriptor information from a multi handle
otherwise remove any others. The \fIcurl_multi_perform(3)\fP function should be
called as soon as one of them is ready to be read from or written to.
-To be sure to have up-to-date results, you should call
-\fIcurl_multi_perform\fP until it does not return CURLM_CALL_MULTI_PERFORM
-prior to calling \fIcurl_multi_fdset\fP. This will make sure that libcurl has
-updated the handles' socket states.
-
If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when
this function returns. Otherwise it will contain the higher descriptor number
-libcurl set.
+libcurl set. When libcurl returns -1 in \fImax_fd\fP, it is because libcurl
+currently does something that isn't possible for your application to monitor
+with a socket and unfortunately you can then not know exactly when the current
+action is completed using select(). When max_fd returns with -1, you need to
+wait a while and then proceed and call \fIcurl_multi_perform\fP anyway. How
+long to wait? I would suggest 100 milliseconds at least, but you may want to
+test it out in your own particular conditions to find a suitable value.
-You should also be aware that when doing select(), you should consider using a
-rather small (single-digit number of seconds) timeout and call
-\fIcurl_multi_perform\fP regularly - even if no activity has been seen on the
-fd_sets - as otherwise libcurl-internal retries and timeouts may not work as
-you'd think and want.
+When doing select(), you should use \fBcurl_multi_timeout\fP to figure out how
+long to wait for action. Call \fIcurl_multi_perform\fP even if no activity has
+been seen on the fd_sets after the timeout expires as otherwise internal
+retries and timeouts may not work as you'd think and want.
-Starting with libcurl 7.16.0, you should use \fBcurl_multi_timeout\fP to
-figure out how long to wait for action.
+If one of the sockets used by libcurl happens to be larger than what can be
+set in an fd_set, which on POSIX systems means that the file descriptor is
+larger than FD_SETSIZE, then libcurl will try to not set it. Setting a too
+large file descriptor in an fd_set implies an out of bounds write which can
+cause crashes, or worse. The effect of NOT storing it will possibly save you
+from the crash, but will make your program NOT wait for sockets it should wait
+for...
.SH RETURN VALUE
CURLMcode type, general libcurl multi interface error code. See
\fIlibcurl-errors(3)\fP
projects / platform / upstream / curl.git / blobdiff