Control.Concurrent.QSem

QSem is a quantity semaphore in which the resource is acquired and released in units of one. It provides guaranteed FIFO ordering for satisfying blocked waitQSem calls.

The pattern

bracket_ waitQSem signalQSem (...)

is safe; it never loses a unit of the resource.

Build a new QSem with a supplied initial quantity. The initial quantity must be at least 0.

Wait for a unit to become available.

Signal that a unit of the QSem is available.