Function CONDITION-WAIT

Syntax:

condition-wait condition-variable lock &key timeout => generalized-boolean

Arguments and values:

condition-variable -> a condition-variable object.
lock -> a lock object.
timeout -> a non-negative real number.
generalized-boolean -> a generalized boolean.

Description:

Atomically release lock and enqueue the calling thread waiting for condition-variable. The thread will resume when another thread has notified it using condition-notify; it may also resume if interrupted by some external event or in other implementation-dependent circumstances: the caller must always test on waking that there is threading to be done, instead of assuming that it can go ahead.
It is an error to call this function unless from the thread that holds lock.

If timeout is nil or not provided, the call blocks until a notification is received.
If timeout is non-nil, the call will return after at most timeout seconds (approximately), whether or not a notification has occurred.

Either true or false will be returned. false indicates that the timeout has expired without receiving a notification. true indicates that a notification was received.

Exceptional situations:

Signals an error of type type-error if condition-variable is not a condition-variable object.
Signals an error of type type-error if lock is not a lock object.
Signals an error of type type-error if timeout is neither nil nor a non-negative real number.

See also:

condition-notify, condition-broadcast

Notes:

Due to implementation limitations, there is the possibility of spurious wakeups, i.e. for condition-wait to return true without the underlying condition being satisfied. Correct code must always check whether the condition is satisfied, and otherwise call condition-wait again, typically in a loop.