mirror of
https://github.com/moparisthebest/curl
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110 lines
4.4 KiB
Groff
110 lines
4.4 KiB
Groff
.\" **************************************************************************
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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 but has no internal thread synchronization. You may have
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to provide your own locking should you meet any of the thread safety exceptions
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below.
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\fBHandles.\fP You must \fBnever\fP share the same handle in multiple threads.
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You can pass the handles around among threads, but you must never use a single
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handle from more than one thread at any given time.
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\fBShared objects.\fP You can share certain data between multiple handles by
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using the share interface but you must provide your own locking and set
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\fIcurl_share_setopt(3)\fP CURLSHOPT_LOCKFUNC and CURLSHOPT_UNLOCKFUNC.
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\fBSSL/TLS handlers.\fP If you are accessing HTTPS or FTPS URLs in a
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multi-threaded manner, you are then of course using the underlying SSL library
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multi-threaded and those libs might have their own requirements on this issue.
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You may need to 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 used by libcurl in a way that is fully thread-safe.
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.IP WinSSL
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The engine is used by libcurl in a way that is fully thread-safe.
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.IP wolfSSL
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The engine is used by libcurl in a way that is fully thread-safe.
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.RE
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\fBSignals.\fP Signals are used for timing out name resolves (during DNS
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lookup) - when built without using either the c-ares or threaded resolver
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backends. When using multiple threads you should set the
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\fICURLOPT_NOSIGNAL(3)\fP option to 1 for all handles. Everything will or might
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work fine except that timeouts are not honored during the DNS lookup - which
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you can work around by building libcurl with c-ares support. c-ares is a
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library that provides asynchronous name resolves. On some platforms, libcurl
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simply will not function properly multi-threaded unless this option is set.
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\fBgethostby* functions and other system calls.\fP These functions, provided by
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your operating system, must be thread safe. It is very important that libcurl
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can find and use thread safe versions of these and other system calls, as
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otherwise it can't function fully thread safe. Some operating systems are known
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to have faulty thread implementations. We have previously received problem
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reports on *BSD (at least in the past, they may be working fine these days).
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Some operating systems that are known to have solid and working thread support
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are Linux, Solaris and Windows.
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\fBcurl_global_* functions.\fP These functions are not thread safe. If you are
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using libcurl with multiple threads it is especially important that before use
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you 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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