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<!-- This manual is last updated 4 March 2015 for version
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<title>GnuTLS 3.5.3: Thread safety</title>
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<a name="Thread-safety"></a>
<div class="header">
<p>
Next: <a href="Running-in-a-sandbox.html#Running-in-a-sandbox" accesskey="n" rel="next">Running in a sandbox</a>, Previous: <a href="Debugging-and-auditing.html#Debugging-and-auditing" accesskey="p" rel="prev">Debugging and auditing</a>, Up: <a href="Introduction-to-the-library.html#Introduction-to-the-library" accesskey="u" rel="up">Introduction to the library</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Thread-safety-1"></a>
<h4 class="subsection">6.1.5 Thread safety</h4>
<a name="index-thread-safety"></a>
<p>The <acronym>GnuTLS</acronym> library is thread safe by design, meaning that
objects of the library such as TLS sessions, can be safely divided across
threads as long as a single thread accesses a single object. This is
sufficient to support a server which handles several sessions per thread.
If, however, an object needs to be shared across threads then access must be
protected with a mutex. Read-only access to objects, for example the
credentials holding structures, is also thread-safe.
</p>
<p>A <code>gnutls_session_t</code> object can be shared by two threads, one sending,
the other receiving. In that case rehandshakes, if required,
must only be handled by a single thread being active. The termination of a session
should be handled, either by a single thread being active, or by the sender thread
using <a href="Core-TLS-API.html#gnutls_005fbye">gnutls_bye</a> with <code>GNUTLS_SHUT_WR</code> and the receiving thread
waiting for a return value of zero.
</p>
<p>The random generator of the cryptographic back-end, utilizes mutex locks (e.g., pthreads on GNU/Linux and CriticalSection on Windows)
which are setup by <acronym>GnuTLS</acronym> on library initialization. Prior to version 3.3.0
they were setup by calling <a href="Core-TLS-API.html#gnutls_005fglobal_005finit">gnutls_global_init</a>. On special systems
you could manually specify the locking system using
the function <a href="Core-TLS-API.html#gnutls_005fglobal_005fset_005fmutex">gnutls_global_set_mutex</a> before calling any other
GnuTLS function. Setting mutexes manually is not recommended.
An example of non-native thread usage is shown below.
</p>
<div class="example">
<pre class="example">#include <gnutls/gnutls.h>
int main()
{
/* When the system mutexes are not to be used
* gnutls_global_set_mutex() must be called explicitly
*/
gnutls_global_set_mutex (mutex_init, mutex_deinit,
mutex_lock, mutex_unlock);
}
</pre></div>
<dl>
<dt><a name="index-gnutls_005fglobal_005fset_005fmutex"></a>Function: <em>void</em> <strong>gnutls_global_set_mutex</strong> <em>(mutex_init_func <var>init</var>, mutex_deinit_func <var>deinit</var>, mutex_lock_func <var>lock</var>, mutex_unlock_func <var>unlock</var>)</em></dt>
<dd><p><var>init</var>: mutex initialization function
</p>
<p><var>deinit</var>: mutex deinitialization function
</p>
<p><var>lock</var>: mutex locking function
</p>
<p><var>unlock</var>: mutex unlocking function
</p>
<p>With this function you are allowed to override the default mutex
locks used in some parts of gnutls and dependent libraries. This function
should be used if you have complete control of your program and libraries.
Do not call this function from a library, or preferably from any application
unless really needed to. GnuTLS will use the appropriate locks for the running
system.
</p>
<p>This function must be called prior to any other gnutls function.
</p>
<p><strong>Since:</strong> 2.12.0
</p></dd></dl>
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Next: <a href="Running-in-a-sandbox.html#Running-in-a-sandbox" accesskey="n" rel="next">Running in a sandbox</a>, Previous: <a href="Debugging-and-auditing.html#Debugging-and-auditing" accesskey="p" rel="prev">Debugging and auditing</a>, Up: <a href="Introduction-to-the-library.html#Introduction-to-the-library" accesskey="u" rel="up">Introduction to the library</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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