curl_multi_fdset: explain the fd_set arguments

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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.

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 the \fIread_fd_set\fP argument is not a null pointer, it points to an

object of type fd_set that on returns specifies the file descriptors to be

checked for being ready to read.

If the \fIwrite_fd_set\fP argument is not a null pointer, it points to an

object of type fd_set that on return specifies the file descriptors to be

checked for being ready to write.

If the \fIexc_fd_set\fP argument is not a null pointer, it points to an object

of type fd_set that on return specifies the file descriptors to be checked for

error conditions pending.

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

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.

long to wait? We 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

\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) "

.BR curl_multi_timeout "(3), " curl_multi_perform "(3), " select "(2) "