7.1.4 Thread safety

The GnuTLS 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.

The random generator of the cryptographic back-end, is not thread safe and requires mutex locks which are setup by GnuTLS. Applications can either call gnutls_global_init which will initialize the default operating system provided locks (i.e. pthreads on GNU/Linux and CriticalSection on Windows), or manually specify the locking system using the function gnutls_global_set_mutex before calling gnutls_global_init. Setting mutexes manually is recommended only for applications that have full control of the underlying libraries. If this is not the case, the use of the operating system defaults is recommended. An example of non-native thread usage is shown below.

#include <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);
   gnutls_global_init();
}

• gnutls_global_set_mutex

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