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libcurl-thread.3: minor reformatting

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Daniel Stenberg 2015-07-31 23:19:02 +02:00
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docs/libcurl/libcurl-thread.3
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@ -23,7 +23,7 @@
.TH libcurl-thread 3 "13 Jul 2015" "libcurl" "libcurl thread safety"
.SH NAME
libcurl-thread \- libcurl thread safety
.SH "Multi-threading Issues"
.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.
@ -35,80 +35,61 @@ 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.
\fBSSL/TLS handlers.\fP 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:
.RS
.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
http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION
http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION
http://curl.haxx.se/libcurl/c/opensslthreadlock.html
http://curl.haxx.se/libcurl/c/opensslthreadlock.html
.IP GnuTLS
http://gnutls.org/manual/html_node/Thread-safety.html
http://gnutls.org/manual/html_node/Thread-safety.html
.IP NSS
is claimed to be thread-safe already without anything required.
thread-safe already without anything required.
.IP PolarSSL
Required actions unknown.
Required actions unknown.
.IP yassl
Required actions unknown.
Required actions unknown.
.IP axTLS
Required actions unknown.
Required actions unknown.
.IP Secure-Transport
The engine is used by libcurl in a way that is fully thread-safe.
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.
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.
.RE
\fBSignals.\fP 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.
\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.
\fBcurl_global_* functions.\fP 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
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.
\fBMemory functions.\fP 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 "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.