TSemaphore
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object TSemaphore
| package stm
Acquires a single permit in transactional context.
Acquires the specified number of permits in a transactional context.
Returns the number of available permits in a transactional context.
Releases a single permit in a transactional context.
Releases the specified number of permits in a transactional context
Executes the specified effect, acquiring a permit immediately before the effect begins execution and releasing it immediately after the effect completes execution, whether by success, failure, or interruption.
Returns a scoped effect that describes acquiring a permit as the acquire
action and releasing it as the release action.
Executes the specified effect, acquiring the specified number of permits immediately before the effect begins execution and releasing them immediately after the effect completes execution, whether by success, failure, or interruption.
Returns a scoped effect that describes acquiring the specified number of permits and releasing them when the scope is closed.
A
TSemaphoreis a semaphore that can be composed transactionally. Because of the extremely high performance of ZIO's implementation of software transactional memoryTSemaphorecan support both controlling access to some resource on a standalone basis as well as composing with other STM data structures to solve more advanced concurrency problems.For basic use cases, the most idiomatic way to work with a semaphore is to use the
withPermitoperator, which acquires a permit before executing someZIOeffect and release the permit immediately afterward. The permit is guaranteed to be released immediately after the effect completes execution, whether by success, failure, or interruption. Attempting to acquire a permit when a sufficient number of permits are not available will semantically block until permits become available without blocking any underlying operating system threads. If you want to acquire more than one permit at a time you can usewithPermits, which allows specifying a number of permits to acquire. You can also usewithPermitScopedorwithPermitsScopedto acquire and release permits within the context of a scoped effect for composing with other resources.For more advanced concurrency problems you can use the
acquireandreleaseoperators directly, or their variantsacquireNandreleaseN, all of which return STM transactions. Thus, they can be composed to form larger STM transactions, for example acquiring permits from two different semaphores transactionally and later releasing them transactionally to safely synchronize on access to two different mutable variables.