annotate mupdf-source/thirdparty/curl/docs/libcurl/curl_multi_fdset.3 @ 2:b50eed0cc0ef upstream

ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1 .\" **************************************************************************
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2 .\" * _ _ ____ _
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3 .\" * Project ___| | | | _ \| |
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4 .\" * / __| | | | |_) | |
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5 .\" * | (__| |_| | _ <| |___
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6 .\" * \___|\___/|_| \_\_____|
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7 .\" *
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8 .\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
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9 .\" *
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10 .\" * This software is licensed as described in the file COPYING, which
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11 .\" * you should have received as part of this distribution. The terms
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12 .\" * are also available at https://curl.haxx.se/docs/copyright.html.
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13 .\" *
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14 .\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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15 .\" * copies of the Software, and permit persons to whom the Software is
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16 .\" * furnished to do so, under the terms of the COPYING file.
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17 .\" *
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18 .\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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19 .\" * KIND, either express or implied.
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20 .\" *
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21 .\" **************************************************************************
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22 .TH curl_multi_fdset 3 "2 Jan 2006" "libcurl 7.16.0" "libcurl Manual"
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23 .SH NAME
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24 curl_multi_fdset - extracts file descriptor information from a multi handle
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25 .SH SYNOPSIS
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26 .nf
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27 #include <curl/curl.h>
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29 CURLMcode curl_multi_fdset(CURLM *multi_handle,
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30 fd_set *read_fd_set,
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31 fd_set *write_fd_set,
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32 fd_set *exc_fd_set,
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33 int *max_fd);
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34 .ad
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35 .SH DESCRIPTION
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36 This function extracts file descriptor information from a given multi_handle.
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37 libcurl returns its fd_set sets. The application can use these to select() on,
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38 but be sure to FD_ZERO them before calling this function as
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39 \fIcurl_multi_fdset(3)\fP only adds its own descriptors, it doesn't zero or
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40 otherwise remove any others. The \fIcurl_multi_perform(3)\fP function should
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41 be called as soon as one of them is ready to be read from or written to.
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42
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43 If the \fIread_fd_set\fP argument is not a null pointer, it points to an
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44 object of type fd_set that on returns specifies the file descriptors to be
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45 checked for being ready to read.
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46
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47 If the \fIwrite_fd_set\fP argument is not a null pointer, it points to an
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48 object of type fd_set that on return specifies the file descriptors to be
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49 checked for being ready to write.
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50
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51 If the \fIexc_fd_set\fP argument is not a null pointer, it points to an object
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52 of type fd_set that on return specifies the file descriptors to be checked for
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53 error conditions pending.
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54
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55 If no file descriptors are set by libcurl, \fImax_fd\fP will contain -1 when
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56 this function returns. Otherwise it will contain the highest descriptor number
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57 libcurl set. When libcurl returns -1 in \fImax_fd\fP, it is because libcurl
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58 currently does something that isn't possible for your application to monitor
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59 with a socket and unfortunately you can then not know exactly when the current
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60 action is completed using select(). You then need to wait a while before you
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61 proceed and call \fIcurl_multi_perform(3)\fP anyway. How long to wait? Unless
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62 \fIcurl_multi_timeout(3)\fP gives you a lower number, we suggest 100
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63 milliseconds or so, but you may want to test it out in your own particular
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64 conditions to find a suitable value.
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65
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66 When doing select(), you should use \fIcurl_multi_timeout(3)\fP to figure out
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67 how long to wait for action. Call \fIcurl_multi_perform(3)\fP even if no
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68 activity has been seen on the fd_sets after the timeout expires as otherwise
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69 internal retries and timeouts may not work as you'd think and want.
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70
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71 If one of the sockets used by libcurl happens to be larger than what can be
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72 set in an fd_set, which on POSIX systems means that the file descriptor is
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73 larger than FD_SETSIZE, then libcurl will try to not set it. Setting a too
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74 large file descriptor in an fd_set implies an out of bounds write which can
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75 cause crashes, or worse. The effect of NOT storing it will possibly save you
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76 from the crash, but will make your program NOT wait for sockets it should wait
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77 for...
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78 .SH RETURN VALUE
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79 CURLMcode type, general libcurl multi interface error code. See
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80 \fIlibcurl-errors(3)\fP
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81 .SH "SEE ALSO"
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82 .BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
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83 .BR curl_multi_wait "(3), "
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84 .BR curl_multi_timeout "(3), " curl_multi_perform "(3), " select "(2) "