Prolog may be called safely from any Python thread. The Prolog
execution is embraced with Py_BEGIN_ALLOW_THREADS and
Py_END_ALLOW_THREADS, which implies that Python is allowed
to switch to another thread while Prolog is doing its work.
If the calling Python thread is not the one that initiated Janus,
janus.query_once() and janus.query()
attach and detach a temporary Prolog engine using PL_thread_attach_engine()
and
PL_thread_destroy_engine(). This is relatively costly. In
addition we allow associating a Prolog engine persistently with the
calling thread.
- int janus.engine()
- Return the identifier of the Prolog engine associated to the current
thread, -1 if no engine is attached or -2 if this version of Prolog does
not support engines.
- int janus.attach_engine()
- Attach a Prolog engine to the current thread using
PL_thread_attach_engine(). On success, return the integer thread
id of the created Prolog engine.8The
current implementation passes
NULL to PL_thread_attach_engine().
Future versions may provide access to the creation attributes.
If the thread already has an engine the attach count is
incremented and the current engine id is returned. The engine is
detached after a matching number of calls to
janus.detach_engine()
- None janus.detach_engine()
- Decrement the attach count of the attached Prolog engine. Destroy
the engine if this count drops to zero. Raises an exception of the
calling thread is not attached to a Prolog engine.
