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## with-process-lock

Arguments: (lock &key timeout norecursive seized whostate) &body body

This macro executes the body with lock seized. Unlike process-lock, with-process-lock protects against a single process trying to seize a lock it already owns. If executed dynamically inside another with-process-lock for the same lock, and if norecursive is `nil`, with-process-lock behaves as if the lock was seized successfully, and the body is executed. If norecursive is `t`, an error is signaled. The default value of norecursive is `nil`.

The seized argument, if specified, must be a bound variable. In the macro body, this variable will be set to `nil` if the lock was not already held and set to `t` if it was already held. This allows avoiding recursion issues.

If a timeout is specified and non-`nil`, the value should be a real number; the units are seconds. 0 or a negative timeout value times out immediately (they seize the lock only if it is currently available). A value of `nil` is equivalent to an unspecified timeout argument. timeout works as it does for process-lock.

If the form times out before the lock is available, the with-process-lock form returns `nil` without the body being executed. If you want to take specific action if the lock does not become available when timeout is specified, use a form like this:

    (block ok
      (with-process-lock (lock :timeout 10)
        (return-from ok (progn body-forms ...)))
      (... action if lock never becomes available ...))

See also process-unlock, process-lock-locker, and make-process-lock.

See About design considerations for event-driven applications in cgide.htm and post-funcall-in-cg-process if you intend to call this function is a Common Graphics process.

See multiprocessing.htm for general information on multiprocessing in Allegro CL and see Process locks for more information on process locks in Allegro CL.

Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.2 page.
Created 2012.5.30.

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| Allegro CL version 9.0 Unrevised from 8.2 to 9.0. 8.2 version