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Diffstat (limited to 'docs/libcurl/gnurl_multi_fdset.3')
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1 files changed, 84 insertions, 0 deletions
diff --git a/docs/libcurl/gnurl_multi_fdset.3 b/docs/libcurl/gnurl_multi_fdset.3 new file mode 100644 index 000000000..81fb4b1dc --- /dev/null +++ b/docs/libcurl/gnurl_multi_fdset.3 @@ -0,0 +1,84 @@ +.\" ************************************************************************** +.\" * _ _ ____ _ +.\" * Project ___| | | | _ \| | +.\" * / __| | | | |_) | | +.\" * | (__| |_| | _ <| |___ +.\" * \___|\___/|_| \_\_____| +.\" * +.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al. +.\" * +.\" * This software is licensed as described in the file COPYING, which +.\" * you should have received as part of this distribution. The terms +.\" * are also available at https://curl.haxx.se/docs/copyright.html. +.\" * +.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell +.\" * copies of the Software, and permit persons to whom the Software is +.\" * furnished to do so, under the terms of the COPYING file. +.\" * +.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY +.\" * KIND, either express or implied. +.\" * +.\" ************************************************************************** +.TH gnurl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libgnurl Manual" +.SH NAME +curl_multi_fdset - extracts file descriptor information from a multi handle +.SH SYNOPSIS +.nf +#include <gnurl/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 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 highest 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(). You then need to wait a while before you +proceed and call \fIcurl_multi_perform(3)\fP anyway. How long to wait? Unless +\fIcurl_multi_timeout(3)\fP gives you a lower number, we suggest 100 +milliseconds or so, but you may want to test it out in your own particular +conditions to find a suitable value. + +When doing select(), you should use \fIcurl_multi_timeout(3)\fP to figure out +how long to wait for action. Call \fIcurl_multi_perform(3)\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_wait "(3), " +.BR curl_multi_timeout "(3), " curl_multi_perform "(3), " select "(2) " |