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Diffstat (limited to 'docs/libcurl/libcurl-thread.3')
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diff --git a/docs/libcurl/libcurl-thread.3 b/docs/libcurl/libcurl-thread.3 new file mode 100644 index 00000000..379ca8ff --- /dev/null +++ b/docs/libcurl/libcurl-thread.3 @@ -0,0 +1,105 @@ +.\" ************************************************************************** +.\" * _ _ ____ _ +.\" * Project ___| | | | _ \| | +.\" * / __| | | | |_) | | +.\" * | (__| |_| | _ <| |___ +.\" * \___|\___/|_| \_\_____| +.\" * +.\" * Copyright (C) 2015 - 2016, 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 libcurl-thread 3 "13 Jul 2015" "libcurl" "libcurl thread safety" +.SH NAME +libcurl-thread \- libcurl thread safety +.SH "Multi-threading with libcurl" +libcurl is thread safe but has no internal thread synchronization. You may have +to provide your own locking should you meet any of the thread safety exceptions +below. + +\fBHandles.\fP You must \fBnever\fP share the same handle in multiple threads. +You can pass the handles around among threads, but you must never use a single +handle from more than one thread at any given time. + +\fBShared objects.\fP You can share certain data between multiple handles by +using the share interface but you must provide your own locking and set +\fIcurl_share_setopt(3)\fP CURLSHOPT_LOCKFUNC and CURLSHOPT_UNLOCKFUNC. +.SH TLS +If you are accessing HTTPS or FTPS URLs in a multi-threaded manner, you are +then of course using the underlying SSL library multi-threaded and those libs +might have their own requirements on this issue. You may need to provide one +or two functions to allow it to function properly: +.IP OpenSSL +OpenSSL 1.1.0 "can be safely used in multi-threaded applications provided that +support for the underlying OS threading API is built-in." + +https://www.openssl.org/docs/manmaster/crypto/threads.html#DESCRIPTION + +OpenSSL <= 1.0.2 the user must set callbacks. + +https://www.openssl.org/docs/man1.0.2/crypto/threads.html#DESCRIPTION + +https://curl.haxx.se/libcurl/c/opensslthreadlock.html + +.IP GnuTLS +http://gnutls.org/manual/html_node/Thread-safety.html +.IP NSS +thread-safe already without anything required. +.IP PolarSSL +Required actions unknown. +.IP yassl +Required actions unknown. +.IP axTLS +Required actions unknown. +.IP Secure-Transport +The engine is used by libcurl in a way that is fully thread-safe. +.IP WinSSL +The engine is used by libcurl in a way that is fully thread-safe. +.IP wolfSSL +The engine is used by libcurl in a way that is fully thread-safe. +.IP BoringSSL +The engine is used by libcurl in a way that is fully thread-safe. +.SH "Other areas of caution" +.IP Signals +Signals are used for timing out name resolves (during DNS lookup) - when built +without using either the c-ares or threaded resolver backends. When using +multiple threads you should set the \fICURLOPT_NOSIGNAL(3)\fP option to 1L for +all handles. Everything will or might work fine except that timeouts are not +honored during the DNS lookup - which you can work around by building libcurl +with c-ares support. c-ares is a library that provides asynchronous name +resolves. On some platforms, libcurl simply will not function properly +multi-threaded unless this option is set. +.IP "Name resolving" +\fBgethostby* functions and other system calls.\fP These functions, provided +by your operating system, must be thread safe. It is very important that +libcurl can find and use thread safe versions of these and other system calls, +as otherwise it can't function fully thread safe. Some operating systems are +known to have faulty thread implementations. We have previously received +problem reports on *BSD (at least in the past, they may be working fine these +days). Some operating systems that are known to have solid and working thread +support are Linux, Solaris and Windows. +.IP "curl_global_* functions" +These functions are not thread safe. If you are using libcurl with multiple +threads it is especially important that before use you call +\fIcurl_global_init(3)\fP or \fIcurl_global_init_mem(3)\fP to explicitly +initialize the library and its dependents, rather than rely on the "lazy" +fail-safe initialization that takes place the first time +\fIcurl_easy_init(3)\fP is called. For an in-depth explanation refer to +\fIlibcurl(3)\fP section \fBGLOBAL CONSTANTS\fP. +.IP "Memory functions" +These functions, provided either by your operating system or your own +replacements, must be thread safe. You can use \fIcurl_global_init_mem(3)\fP +to set your own replacement memory functions. +.IP "Non-safe functions" +\fICURLOPT_DNS_USE_GLOBAL_CACHE(3)\fP is not thread-safe. |