Function: SB-THREAD:CONDITION-WAIT

Atomically release MUTEX and start waiting on QUEUE until another thread wakes us up using either CONDITION-NOTIFY or CONDITION-BROADCAST on QUEUE, at which point we re-acquire MUTEX and return T.

Spurious wakeups are possible.

If TIMEOUT is given, it is the maximum number of seconds to wait, including both waiting for the wakeup and the time to re-acquire MUTEX. When neither a wakeup nor a re-acquisition occurs within the given time, returns NIL without re-acquiring MUTEX.

If CONDITION-WAIT unwinds, it may do so with or without MUTEX being held.

Important: Since CONDITION-WAIT may return without CONDITION-NOTIFY or CONDITION-BROADCAST having occurred, the correct way to write code that uses CONDITION-WAIT is to loop around the call, checking the associated data:

(defvar data nil) (defvar queue (make-waitqueue)) (defvar lock (make-mutex))

;; Consumer (defun pop-data (&optional timeout) (with-mutex (lock) (loop until data do (or (condition-wait queue lock :timeout timeout) ;; Lock not held, must unwind without touching data. (return-from pop-data nil))) (pop data)))

;; Producer (defun push-data (data) (with-mutex (lock) (push data data) (condition-notify queue)))

Lambda list

(sb-thread::queue sb-thread:mutex &key sb-thread::timeout)