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com.twitter.concurrent

AsyncSemaphore

Related Docs: object AsyncSemaphore | package concurrent

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class AsyncSemaphore extends AnyRef

An AsyncSemaphore is a traditional semaphore but with asynchronous execution.

Grabbing a permit returns a Future[Permit].

Basic usage:

val semaphore = new AsyncSemaphore(n)
...
semaphore.acquireAndRun() {
  somethingThatReturnsFutureT()
}

Calls to acquire() and acquireAndRun are serialized, and tickets are given out fairly (in order of arrival).

See also: AsyncMutex for a mutex version.

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Instance Constructors

new AsyncSemaphore(initialPermits: Int, maxWaiters: Int)

Constructs a semaphore with maxWaiters as the limit on the number of waiters for permits.
Constructs a semaphore with maxWaiters as the limit on the number of waiters for permits.
initialPermits
must be positive
maxWaiters
must be non-negative
new AsyncSemaphore(initialPermits: Int)

Constructs a semaphore with no limit on the max number of waiters for permits.
Constructs a semaphore with no limit on the max number of waiters for permits.
initialPermits
must be positive
new AsyncSemaphore(initialPermits: Int, maxWaiters: Option[Int])

Attributes
protected

Value Members

final def !=(arg0: Any): Boolean

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final def ##(): Int

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final def ==(arg0: Any): Boolean

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def acquire(): Future[Permit]

Acquire a Permit, asynchronously.
Acquire a Permit, asynchronously. Be sure to permit.release() in a
- finally block of your onSuccess callback - ensure block of your future chain
Interrupting this future is only advisory, and will not release the permit if the future has already been satisfied.
returns
a Future[Permit] when the Future is satisfied, computation can proceed, or a Future.Exception[RejectedExecutionException]if the configured maximum number of waiters would be exceeded.

Note
This method always return the same instance of Permit.
def acquireAndRun[T](func: ⇒ Future[T]): Future[T]

Execute the function asynchronously when a permit becomes available.
Execute the function asynchronously when a permit becomes available.
If the function throws a non-fatal exception, the exception is returned as part of the Future. For all exceptions, the permit would be released before returning.
returns
a Future[T] equivalent to the return value of the input function. If the configured maximum value of waitq is reached, Future.Exception[RejectedExecutionException] is returned.
def acquireAndRunSync[T](func: ⇒ T): Future[T]

Execute the function when a permit becomes available.
Execute the function when a permit becomes available.
If the function throws an exception, the exception is returned as part of the Future. For all exceptions, the permit would be released before returning.
returns
a Future[T] equivalent to the return value of the input function. If the configured maximum value of waitq is reached, Future.Exception[RejectedExecutionException] is returned.
final def asInstanceOf[T0]: T0

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def clone(): AnyRef

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protected[java.lang]
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@throws( ... )
final def eq(arg0: AnyRef): Boolean

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def equals(arg0: Any): Boolean

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def fail(exc: Throwable): Unit

Fail the semaphore and stop it from distributing further permits.
Fail the semaphore and stop it from distributing further permits. Subsequent attempts to acquire a permit fail with exc. This semaphore's queued waiters are also failed with exc.
def finalize(): Unit

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protected[java.lang]
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@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

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def hashCode(): Int

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final def isInstanceOf[T0]: Boolean

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final def ne(arg0: AnyRef): Boolean

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final def notify(): Unit

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final def notifyAll(): Unit

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def numInitialPermits: Int
def numPermitsAvailable: Int
def numWaiters: Int
final def synchronized[T0](arg0: ⇒ T0): T0

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def toString(): String

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final def wait(): Unit

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@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

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@throws( ... )
final def wait(arg0: Long): Unit

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