Function

Summary

Acquires units from a semaphore.

Package

mp

Signature

semaphore-acquire sem &key timeout wait-reason count => flag

Arguments

sem

A semaphore.

timeout

An integer or nil .

wait-reason

A string or nil .

count

A non-negative fixnum.

Values

flag

A generalized boolean.

Description

The function semaphore-acquire acquires count units from the semaphore sem .

It attempts to atomically decrement the semaphore's unit count by count (which defaults to 1) and returns true if this would give a non negative unit count.

If decrementing the semaphore's unit count would result in a negative number, then semaphore-acquire waits until the semaphore's unit count is larger than count and tries again. If wait-reason is true, then it is used as the thread's wait-reason when waiting for the semaphore.

If timeout is nil , semaphore-acquire can wait forever. If timeout is true, it should be an integer. If the semaphore count cannot be decremented within timeout seconds, then semaphore-acquire returns false and the semaphore is unaffected. Pass timeout 0 if you do not want to wait at all.

See also

make-semaphore
semaphore-count
semaphore-release
semaphore-wait-count