A mutex is an exclusive lock. At any moment, zero or one threads may own a mutex. If a thread attempts to acquire a mutex, and the mutex is already owned by some other thread, then the acquiring thread will block until the mutex becomes available.
Emacs Lisp mutexes are of a type called recursive, which means that a thread can re-acquire a mutex it owns any number of times. A mutex keeps a count of how many times it has been acquired, and each acquisition of a mutex must be paired with a release. The last release by a thread of a mutex reverts it to the unowned state, potentially allowing another thread to acquire the mutex.
mutexp
object ¶This function returns t
if object represents an Emacs
mutex, nil
otherwise.
make-mutex
&optional name ¶Create a new mutex and return it. If name is specified, it is a name given to the mutex. It must be a string. The name is for debugging purposes only; it has no meaning to Emacs.
mutex-name
mutex ¶Return the name of mutex, as specified to make-mutex
.
mutex-lock
mutex ¶This will block until this thread acquires mutex, or until this
thread is signaled using thread-signal
. If mutex is
already owned by this thread, this simply returns.
mutex-unlock
mutex ¶Release mutex. If mutex is not owned by this thread, this will signal an error.
with-mutex
mutex body… ¶This macro is the simplest and safest way to evaluate forms while holding a mutex. It acquires mutex, invokes body, and then releases mutex. It returns the result of body.