Return to libcurl-thread.3 CVS log

Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / curl / docs / libcurl

Annotation of embedaddon/curl/docs/libcurl/libcurl-thread.3, revision 1.1.1.1

1.1       misho       1: .\" **************************************************************************
                      2: .\" *                                  _   _ ____  _
                      3: .\" *  Project                     ___| | | |  _ \| |
                      4: .\" *                             / __| | | | |_) | |
                      5: .\" *                            | (__| |_| |  _ <| |___
                      6: .\" *                             \___|\___/|_| \_\_____|
                      7: .\" *
                      8: .\" * Copyright (C) 2015 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
                      9: .\" *
                     10: .\" * This software is licensed as described in the file COPYING, which
                     11: .\" * you should have received as part of this distribution. The terms
                     12: .\" * are also available at https://curl.haxx.se/docs/copyright.html.
                     13: .\" *
                     14: .\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
                     15: .\" * copies of the Software, and permit persons to whom the Software is
                     16: .\" * furnished to do so, under the terms of the COPYING file.
                     17: .\" *
                     18: .\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
                     19: .\" * KIND, either express or implied.
                     20: .\" *
                     21: .\" **************************************************************************
                     22: .\"
                     23: .TH libcurl-thread 3 "June 30, 2019" "libcurl 7.70.0" "libcurl thread safety"
                     24: 
                     25: .SH NAME
                     26: libcurl-thread \- libcurl thread safety
                     27: .SH "Multi-threading with libcurl"
                     28: libcurl is thread safe but has no internal thread synchronization. You may have
                     29: to provide your own locking should you meet any of the thread safety exceptions
                     30: below.
                     31: 
                     32: \fBHandles.\fP You must \fBnever\fP share the same handle in multiple threads.
                     33: You can pass the handles around among threads, but you must never use a single
                     34: handle from more than one thread at any given time.
                     35: 
                     36: \fBShared objects.\fP You can share certain data between multiple handles by
                     37: using the share interface but you must provide your own locking and set
                     38: \fIcurl_share_setopt(3)\fP CURLSHOPT_LOCKFUNC and CURLSHOPT_UNLOCKFUNC.
                     39: .SH TLS
                     40: If you are accessing HTTPS or FTPS URLs in a multi-threaded manner, you are
                     41: then of course using the underlying SSL library multi-threaded and those libs
                     42: might have their own requirements on this issue.  You may need to provide one
                     43: or two functions to allow it to function properly:
                     44: .IP OpenSSL
                     45: OpenSSL 1.1.0+ "can be safely used in multi-threaded applications provided that
                     46: support for the underlying OS threading API is built-in." In that case the
                     47: engine is used by libcurl in a way that is fully thread-safe.
                     48: 
                     49: https://www.openssl.org/docs/man1.1.0/man3/CRYPTO_THREAD_run_once.html#DESCRIPTION
                     50: 
                     51: OpenSSL <= 1.0.2 the user must set callbacks.
                     52: 
                     53: https://www.openssl.org/docs/man1.0.2/man3/CRYPTO_set_locking_callback.html#DESCRIPTION
                     54: 
                     55: https://curl.haxx.se/libcurl/c/opensslthreadlock.html
                     56: 
                     57: .IP GnuTLS
                     58: https://gnutls.org/manual/html_node/Thread-safety.html
                     59: .IP NSS
                     60: thread-safe already without anything required.
                     61: .IP Secure-Transport
                     62: The engine is used by libcurl in a way that is fully thread-safe.
                     63: .IP WinSSL
                     64: The engine is used by libcurl in a way that is fully thread-safe.
                     65: .IP wolfSSL
                     66: The engine is used by libcurl in a way that is fully thread-safe.
                     67: .IP BoringSSL
                     68: The engine is used by libcurl in a way that is fully thread-safe.
                     69: .SH "Other areas of caution"
                     70: .IP Signals
                     71: Signals are used for timing out name resolves (during DNS lookup) - when built
                     72: without using either the c-ares or threaded resolver backends. When using
                     73: multiple threads you should set the \fICURLOPT_NOSIGNAL(3)\fP option to 1L for
                     74: all handles. Everything will or might work fine except that timeouts are not
                     75: honored during the DNS lookup - which you can work around by building libcurl
                     76: with c-ares or threaded-resolver support. c-ares is a library that provides
                     77: asynchronous name resolves. On some platforms, libcurl simply will not
                     78: function properly multi-threaded unless the \fICURLOPT_NOSIGNAL(3)\fP option
                     79: is set.
                     80: 
                     81: When \fICURLOPT_NOSIGNAL(3)\fP is set to 1L, your application needs to deal
                     82: with the risk of a SIGPIPE (that at least the OpenSSL backend can
                     83: trigger). Note that setting \fICURLOPT_NOSIGNAL(3)\fP to 0L will not work in a
                     84: threaded situation as there will be race where libcurl risks restoring the
                     85: former signal handler while another thread should still ignore it.
                     86: .IP "Name resolving"
                     87: \fBgethostby* functions and other system calls.\fP These functions, provided
                     88: by your operating system, must be thread safe. It is very important that
                     89: libcurl can find and use thread safe versions of these and other system calls,
                     90: as otherwise it can't function fully thread safe. Some operating systems are
                     91: known to have faulty thread implementations. We have previously received
                     92: problem reports on *BSD (at least in the past, they may be working fine these
                     93: days).  Some operating systems that are known to have solid and working thread
                     94: support are Linux, Solaris and Windows.
                     95: .IP "curl_global_* functions"
                     96: These functions are not thread safe. If you are using libcurl with multiple
                     97: threads it is especially important that before use you call
                     98: \fIcurl_global_init(3)\fP or \fIcurl_global_init_mem(3)\fP to explicitly
                     99: initialize the library and its dependents, rather than rely on the "lazy"
                    100: fail-safe initialization that takes place the first time
                    101: \fIcurl_easy_init(3)\fP is called. For an in-depth explanation refer to
                    102: \fIlibcurl(3)\fP section \fBGLOBAL CONSTANTS\fP.
                    103: .IP "Memory functions"
                    104: These functions, provided either by your operating system or your own
                    105: replacements, must be thread safe. You can use \fIcurl_global_init_mem(3)\fP
                    106: to set your own replacement memory functions.
                    107: .IP "Non-safe functions"
                    108: \fICURLOPT_DNS_USE_GLOBAL_CACHE(3)\fP is not thread-safe.