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comparison mupdf-source/thirdparty/curl/docs/libcurl/curl_multi_fdset.3 @ 2:b50eed0cc0ef upstream
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| author | Franz Glasner <fzglas.hg@dom66.de> |
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| date | Mon, 15 Sep 2025 11:43:07 +0200 |
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| 22 .TH curl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libcurl Manual" | |
| 23 .SH NAME | |
| 24 curl_multi_fdset - extracts file descriptor information from a multi handle | |
| 25 .SH SYNOPSIS | |
| 26 .nf | |
| 27 #include <curl/curl.h> | |
| 28 | |
| 29 CURLMcode curl_multi_fdset(CURLM *multi_handle, | |
| 30 fd_set *read_fd_set, | |
| 31 fd_set *write_fd_set, | |
| 32 fd_set *exc_fd_set, | |
| 33 int *max_fd); | |
| 34 .ad | |
| 35 .SH DESCRIPTION | |
| 36 This function extracts file descriptor information from a given multi_handle. | |
| 37 libcurl returns its fd_set sets. The application can use these to select() on, | |
| 38 but be sure to FD_ZERO them before calling this function as | |
| 39 \fIcurl_multi_fdset(3)\fP only adds its own descriptors, it doesn't zero or | |
| 40 otherwise remove any others. The \fIcurl_multi_perform(3)\fP function should | |
| 41 be called as soon as one of them is ready to be read from or written to. | |
| 42 | |
| 43 If the \fIread_fd_set\fP argument is not a null pointer, it points to an | |
| 44 object of type fd_set that on returns specifies the file descriptors to be | |
| 45 checked for being ready to read. | |
| 46 | |
| 47 If the \fIwrite_fd_set\fP argument is not a null pointer, it points to an | |
| 48 object of type fd_set that on return specifies the file descriptors to be | |
| 49 checked for being ready to write. | |
| 50 | |
| 51 If the \fIexc_fd_set\fP argument is not a null pointer, it points to an object | |
| 52 of type fd_set that on return specifies the file descriptors to be checked for | |
| 53 error conditions pending. | |
| 54 | |
| 55 If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when | |
| 56 this function returns. Otherwise it will contain the highest descriptor number | |
| 57 libcurl set. When libcurl returns -1 in \fImax_fd\fP, it is because libcurl | |
| 58 currently does something that isn't possible for your application to monitor | |
| 59 with a socket and unfortunately you can then not know exactly when the current | |
| 60 action is completed using select(). You then need to wait a while before you | |
| 61 proceed and call \fIcurl_multi_perform(3)\fP anyway. How long to wait? Unless | |
| 62 \fIcurl_multi_timeout(3)\fP gives you a lower number, we suggest 100 | |
| 63 milliseconds or so, but you may want to test it out in your own particular | |
| 64 conditions to find a suitable value. | |
| 65 | |
| 66 When doing select(), you should use \fIcurl_multi_timeout(3)\fP to figure out | |
| 67 how long to wait for action. Call \fIcurl_multi_perform(3)\fP even if no | |
| 68 activity has been seen on the fd_sets after the timeout expires as otherwise | |
| 69 internal retries and timeouts may not work as you'd think and want. | |
| 70 | |
| 71 If one of the sockets used by libcurl happens to be larger than what can be | |
| 72 set in an fd_set, which on POSIX systems means that the file descriptor is | |
| 73 larger than FD_SETSIZE, then libcurl will try to not set it. Setting a too | |
| 74 large file descriptor in an fd_set implies an out of bounds write which can | |
| 75 cause crashes, or worse. The effect of NOT storing it will possibly save you | |
| 76 from the crash, but will make your program NOT wait for sockets it should wait | |
| 77 for... | |
| 78 .SH RETURN VALUE | |
| 79 CURLMcode type, general libcurl multi interface error code. See | |
| 80 \fIlibcurl-errors(3)\fP | |
| 81 .SH "SEE ALSO" | |
| 82 .BR curl_multi_cleanup "(3), " curl_multi_init "(3), " | |
| 83 .BR curl_multi_wait "(3), " | |
| 84 .BR curl_multi_timeout "(3), " curl_multi_perform "(3), " select "(2) " |