File: gpgme.info,  Node: Multi-Threading,  Prev: Signal Handling,  Up: Preparation

2.8 Multi-Threading
===================

The GPGME library is mostly thread-safe, and can be used in a
multi-threaded environment but there are some requirements for
multi-threaded use:

   • The function ‘gpgme_check_version’ must be called before any other
     function in the library, because it initializes the thread support
     subsystem in GPGME.  To achieve this in multi-threaded programs,
     you must synchronize the memory with respect to other threads that
     also want to use GPGME.  For this, it is sufficient to call
     ‘gpgme_check_version’ before creating the other threads using
     GPGME(1).

   • Any ‘gpgme_data_t’ and ‘gpgme_ctx_t’ object must only be accessed
     by one thread at a time.  If multiple threads want to deal with the
     same object, the caller has to make sure that operations on that
     object are fully synchronized.

   • Only one thread at any time is allowed to call ‘gpgme_wait’.  If
     multiple threads call this function, the caller must make sure that
     all invocations are fully synchronized.  It is safe to start
     asynchronous operations while a thread is running in gpgme_wait.

   • The function ‘gpgme_strerror’ is not thread safe.  You have to use
     ‘gpgme_strerror_r’ instead.

   ---------- Footnotes ----------

   (1) At least this is true for POSIX threads, as ‘pthread_create’ is a
function that synchronizes memory with respects to other threads.  There
are many functions which have this property, a complete list can be
found in POSIX, IEEE Std 1003.1-2003, Base Definitions, Issue 6, in the
definition of the term “Memory Synchronization”.  For other thread
packages other, more relaxed or more strict rules may apply.