mirror of https://github.com/moparisthebest/curl
libcurl-thread.3: Consolidate thread safety info
This is a new document to consolidate our thread safety information from several documents (curl-www:features, libcurl.3, libcurl-tutorial.3). Each document's section on multi-threading will now point to this one.
This commit is contained in:
Jay Satiro
Daniel Stenberg
parent
7db03e5c21
commit
279965c923
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@ -29,18 +29,19 @@ man_MANS = curl_easy_cleanup.3 curl_easy_getinfo.3 curl_easy_init.3 \
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curl_formadd.3 curl_formfree.3 curl_getdate.3 curl_getenv.3 \
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curl_slist_append.3 curl_slist_free_all.3 curl_version.3 \
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curl_version_info.3 curl_escape.3 curl_unescape.3 curl_free.3 \
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curl_strequal.3 curl_mprintf.3 curl_global_init.3 curl_global_cleanup.3 \
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curl_multi_add_handle.3 curl_multi_cleanup.3 curl_multi_fdset.3 \
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curl_multi_info_read.3 curl_multi_init.3 curl_multi_perform.3 \
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curl_multi_remove_handle.3 curl_share_cleanup.3 curl_share_init.3 \
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curl_share_setopt.3 libcurl.3 libcurl-easy.3 libcurl-multi.3 \
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libcurl-share.3 libcurl-errors.3 curl_easy_strerror.3 \
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curl_strequal.3 curl_mprintf.3 curl_global_init.3 \
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curl_global_cleanup.3 curl_multi_add_handle.3 curl_multi_cleanup.3 \
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curl_multi_fdset.3 curl_multi_info_read.3 curl_multi_init.3 \
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curl_multi_perform.3 curl_multi_remove_handle.3 curl_share_cleanup.3 \
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curl_share_init.3 curl_share_setopt.3 libcurl.3 libcurl-easy.3 \
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libcurl-multi.3 libcurl-share.3 libcurl-errors.3 curl_easy_strerror.3 \
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curl_multi_strerror.3 curl_share_strerror.3 curl_global_init_mem.3 \
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libcurl-tutorial.3 curl_easy_reset.3 curl_easy_escape.3 \
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curl_easy_unescape.3 curl_multi_setopt.3 curl_multi_socket.3 \
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curl_multi_timeout.3 curl_formget.3 curl_multi_assign.3 \
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curl_easy_pause.3 curl_easy_recv.3 curl_easy_send.3 \
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curl_multi_socket_action.3 curl_multi_wait.3 libcurl-symbols.3
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curl_multi_socket_action.3 curl_multi_wait.3 libcurl-symbols.3 \
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libcurl-thread.3
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HTMLPAGES = curl_easy_cleanup.html curl_easy_getinfo.html \
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curl_easy_init.html curl_easy_perform.html curl_easy_setopt.html \
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@ -60,27 +61,28 @@ HTMLPAGES = curl_easy_cleanup.html curl_easy_getinfo.html \
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curl_easy_unescape.html curl_multi_setopt.html curl_multi_socket.html \
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curl_multi_timeout.html curl_formget.html curl_multi_assign.html \
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curl_easy_pause.html curl_easy_recv.html curl_easy_send.html \
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curl_multi_socket_action.html curl_multi_wait.html libcurl-symbols.html
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curl_multi_socket_action.html curl_multi_wait.html \
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libcurl-symbols.html libcurl-thread.html
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PDFPAGES = curl_easy_cleanup.pdf curl_easy_getinfo.pdf \
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curl_easy_init.pdf curl_easy_perform.pdf curl_easy_setopt.pdf \
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curl_easy_duphandle.pdf curl_formadd.pdf curl_formfree.pdf \
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curl_getdate.pdf curl_getenv.pdf curl_slist_append.pdf \
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curl_slist_free_all.pdf curl_version.pdf curl_version_info.pdf \
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curl_getdate.pdf curl_getenv.pdf curl_slist_append.pdf \
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curl_slist_free_all.pdf curl_version.pdf curl_version_info.pdf \
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curl_escape.pdf curl_unescape.pdf curl_free.pdf curl_strequal.pdf \
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curl_mprintf.pdf curl_global_init.pdf curl_global_cleanup.pdf \
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curl_multi_add_handle.pdf curl_multi_cleanup.pdf curl_multi_fdset.pdf \
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curl_multi_info_read.pdf curl_multi_init.pdf curl_multi_perform.pdf \
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curl_multi_remove_handle.pdf curl_share_cleanup.pdf curl_share_init.pdf \
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curl_share_setopt.pdf libcurl.pdf libcurl-multi.pdf libcurl-easy.pdf \
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libcurl-share.pdf libcurl-errors.pdf curl_easy_strerror.pdf \
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curl_multi_strerror.pdf curl_share_strerror.pdf \
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curl_global_init_mem.pdf libcurl-tutorial.pdf curl_easy_reset.pdf \
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curl_easy_escape.pdf curl_easy_unescape.pdf curl_multi_setopt.pdf \
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curl_multi_socket.pdf curl_multi_timeout.pdf curl_formget.pdf \
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curl_multi_assign.pdf curl_easy_pause.pdf curl_easy_recv.pdf \
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curl_easy_send.pdf curl_multi_socket_action.pdf curl_multi_wait.pdf \
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libcurl-symbols.pdf
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curl_multi_remove_handle.pdf curl_share_cleanup.pdf \
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curl_share_init.pdf curl_share_setopt.pdf libcurl.pdf \
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libcurl-multi.pdf libcurl-easy.pdf libcurl-share.pdf \
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libcurl-errors.pdf curl_easy_strerror.pdf curl_multi_strerror.pdf \
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curl_share_strerror.pdf curl_global_init_mem.pdf libcurl-tutorial.pdf \
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curl_easy_reset.pdf curl_easy_escape.pdf curl_easy_unescape.pdf \
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curl_multi_setopt.pdf curl_multi_socket.pdf curl_multi_timeout.pdf \
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curl_formget.pdf curl_multi_assign.pdf curl_easy_pause.pdf \
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curl_easy_recv.pdf curl_easy_send.pdf curl_multi_socket_action.pdf \
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curl_multi_wait.pdf libcurl-symbols.pdf libcurl-thread.pdf
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m4macrodir = $(datadir)/aclocal
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dist_m4macro_DATA = libcurl.m4
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@ -17,6 +17,7 @@
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<br><a href="libcurl-share.html">libcurl-share</a>
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<br><a href="libcurl-errors.html">libcurl-errors</a>
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<br><a href="libcurl-tutorial.html">libcurl-tutorial</a>
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<br><a href="libcurl-thread.html">libcurl-thread</a>
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<H2>Library Functions (A-Z)</H2>
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<a href="curl_easy_cleanup.html">curl_easy_cleanup</A>
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@ -0,0 +1,100 @@
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.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at http://curl.haxx.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.\"
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.TH libcurl-thread 3 "13 Jul 2015" "libcurl" "libcurl thread safety"
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.SH NAME
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libcurl-thread \- libcurl thread safety
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.SH "Multi-threading Issues"
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libcurl is thread safe with the following exceptions:
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Do \fBNOT\fP use library functions to access or modify the same handle
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concurrently from multiple threads. If concurrent access to the same handle
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from multiple threads could be an issue then you must implement your own
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locking to ensure it won't happen.
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Shared objects. You can share certain data between multiple handles by using
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the share interface but you must implement your own locking and set
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\fIcurl_share_setopt(3)\fP CURLSHOPT_LOCKFUNC and CURLSHOPT_UNLOCKFUNC.
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SSL/TLS handlers. If you are accessing HTTPS or FTPS URLs in a multi-threaded
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manner, you are then of course using the underlying SSL library multi-threaded
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and those libs might have their own requirements on this issue. You may need to
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provide one or two functions to allow it to function properly:
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.RS
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.IP OpenSSL
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http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION
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http://curl.haxx.se/libcurl/c/opensslthreadlock.html
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.IP GnuTLS
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http://gnutls.org/manual/html_node/Thread-safety.html
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.IP NSS
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is claimed to be thread-safe already without anything required.
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.IP PolarSSL
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Required actions unknown.
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.IP yassl
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Required actions unknown.
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.IP axTLS
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Required actions unknown.
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.IP Secure-Transport
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The engine is fully thread-safe, and no additional steps are required.
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.RE
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Signals. Signals are used for timing out name resolves (during DNS lookup) -
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when built without using either the c-ares or threaded resolver backends. When
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using multiple threads you should set the \fICURLOPT_NOSIGNAL(3)\fP option to 1
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for all handles. Everything will or might work fine except that timeouts are
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not honored during the DNS lookup - which you can work around by building
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libcurl with c-ares support. c-ares is a library that provides asynchronous
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name resolves. On some platforms, libcurl simply will not function properly
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multi-threaded unless this option is set.
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gethostby* functions and other system calls. These functions, provided by your
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operating system, must be thread safe. It is very important that libcurl can
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find and use thread safe versions of these and other system calls, as otherwise
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it can't function fully thread safe. Some operating systems are known to have
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faulty thread implementations. We have previously received problem reports on
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*BSD (at least in the past, they may be working fine these days). Some
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operating systems that are known to have solid and working thread support are
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Linux, Solaris and Windows.
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curl_global_* functions. These functions are not thread safe. If you are using
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libcurl with multiple threads it is especially important that before use you
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call \fIcurl_global_init(3)\fP to explicitly initialize the library and its
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dependents, rather than rely on the "lazy" fail-safe initialization that takes
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place the first time \fIcurl_easy_init(3)\fP is called. For an in-depth
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explanation refer to \fIlibcurl(3)\fP section \fBGLOBAL CONSTANTS\fP.
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\fICURLOPT_DNS_USE_GLOBAL_CACHE(3)\fP is not thread-safe.
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@ -256,58 +256,8 @@ complication for you. Given simply the URL to a file, libcurl will take care
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of all the details needed to get the file moved from one machine to another.
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.SH "Multi-threading Issues"
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The first basic rule is that you must \fBnever\fP simultaneously share a
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libcurl handle (be it easy or multi or whatever) between multiple
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threads. Only use one handle in one thread at any time. You can pass the
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handles around among threads, but you must never use a single handle from more
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than one thread at any given time.
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libcurl is completely thread safe, except for two issues: signals and SSL/TLS
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handlers. Signals are used for timing out name resolves (during DNS lookup) -
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when built without using either the c-ares or threaded resolver backends.
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If you are accessing HTTPS or FTPS URLs in a multi-threaded manner, you are
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then of course using the underlying SSL library multi-threaded and those libs
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might have their own requirements on this issue. Basically, you need to
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provide one or two functions to allow it to function properly. For all
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details, see this:
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OpenSSL
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http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION
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GnuTLS
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http://gnutls.org/manual/html_node/Thread-safety.html
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NSS
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is claimed to be thread-safe already without anything required.
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PolarSSL
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Required actions unknown.
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yassl
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Required actions unknown.
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axTLS
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Required actions unknown.
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Secure Transport
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The engine is fully thread-safe, and no additional steps are required.
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When using multiple threads you should set the \fICURLOPT_NOSIGNAL(3)\fP
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option to 1 for all handles. Everything will or might work fine except that
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timeouts are not honored during the DNS lookup - which you can work around by
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building libcurl with c-ares support. c-ares is a library that provides
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asynchronous name resolves. On some platforms, libcurl simply will not
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function properly multi-threaded unless this option is set.
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Also, note that \fICURLOPT_DNS_USE_GLOBAL_CACHE(3)\fP is not thread-safe.
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libcurl is thread safe but there are a few exceptions. Refer to
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\fIlibcurl-thread(3)\fP for more information.
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.SH "When It Doesn't Work"
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There will always be times when the transfer fails for some reason. You might
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@ -111,13 +111,8 @@ libcurl works
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.B exactly
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the same, on any of the platforms it compiles and builds on.
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.SH "THREADS"
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Never ever call curl-functions simultaneously using the same handle from
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several threads. libcurl is thread-safe and can be used in any number of
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threads, but you must use separate curl handles if you want to use libcurl in
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more than one thread simultaneously.
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The global environment functions are not thread-safe. See \fBGLOBAL
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CONSTANTS\fP below for details.
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libcurl is thread safe but there are a few exceptions. Refer to
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\fIlibcurl-thread(3)\fP for more information.
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.SH "PERSISTENT CONNECTIONS"
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Persistent connections means that libcurl can re-use the same connection for
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