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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 |
| .SH SYNOPSIS |
| .nf |
| #include <curl/curl.h> |
| |
| CURLMcode curl_multi_fdset(CURLM *multi_handle, |
| fd_set *read_fd_set, |
| fd_set *write_fd_set, |
| fd_set *exc_fd_set, |
| int *max_fd); |
| .ad |
| .SH DESCRIPTION |
| This function extracts file descriptor information from a given multi_handle. |
| libcurl returns its fd_set sets. The application can use these to select() on, |
| but be sure to FD_ZERO them before calling this function as |
| \fIcurl_multi_fdset(3)\fP only adds its own descriptors, it doesn't zero or |
| 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. |
| |
| 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. 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. |
| |
| 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. |
| |
| 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 |
| .SH "SEE ALSO" |
| .BR curl_multi_cleanup "(3), " curl_multi_init "(3), " |
| .BR curl_multi_timeout "(3), " curl_multi_perform "(3) " |
