final class AsyncSemaphore extends GenericSemaphore[Cancelable]
The AsyncSemaphore
is an asynchronous semaphore implementation that
limits the parallelism on Future
execution.
The following example instantiates a semaphore with a maximum parallelism of 10:
val semaphore = AsyncSemaphore(maxParallelism = 10) def makeRequest(r: HttpRequest): Future[HttpResponse] = ??? // For such a task no more than 10 requests // are allowed to be executed in parallel. val future = semaphore.greenLight(() => makeRequest(???))
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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(): CancelableFuture[Unit]
Acquires a single permit.
Acquires a single permit. Alias for
acquireN(1)
.- Annotations
- @UnsafeBecauseImpure()
- See also
withPermit, the preferred way to acquire and release
acquireN for a version that can acquire multiple permits
-
def
acquireN(n: Long): CancelableFuture[Unit]
Acquires
n
permits.Acquires
n
permits.The returned effect semantically blocks until all requested permits are available. Note that acquires are satisfied in strict FIFO order, so given an
AsyncSemaphore
with 2 permits available, anacquireN(3)
will always be satisfied before a later call toacquireN(1)
.- n
number of permits to acquire - must be >= 0
- returns
a future that will complete when the acquisition has succeeded or that can be cancelled, removing the listener from the queue (to prevent memory leaks in race conditions)
- Annotations
- @UnsafeBecauseImpure()
- See also
withPermit, the preferred way to acquire and release
acquire for a version acquires a single permit
-
final
def
asInstanceOf[T0]: T0
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-
def
available(): Long
Returns the number of permits currently available.
Returns the number of permits currently available. Always non-negative.
The protocol is unsafe, the semaphore is used in concurrent settings and thus the value returned isn't stable or reliable. Use with care.
- Annotations
- @UnsafeProtocol() @UnsafeBecauseImpure()
-
def
awaitAvailable(n: Long): CancelableFuture[Unit]
Returns a future that will be complete when the specified number of permits are available.
Returns a future that will be complete when the specified number of permits are available.
The protocol is unsafe because by the time the returned future completes, some other process might have already acquired the available permits and thus usage of
awaitAvailable
can lead to fragile concurrent logic. Use with care.Can be useful for termination logic, for example to execute a piece of logic once all available permits have been released.
- n
is the number of permits waited on
- Annotations
- @UnsafeProtocol() @UnsafeBecauseImpure()
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def
clone(): AnyRef
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def
count(): Long
Obtains a snapshot of the current count.
Obtains a snapshot of the current count. Can be negative.
Like available when permits are available but returns the number of permits callers are waiting for when there are no permits available.
- Annotations
- @UnsafeProtocol() @UnsafeBecauseImpure()
-
def
emptyCancelable: Cancelable
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- AsyncSemaphore → GenericSemaphore
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final
def
eq(arg0: AnyRef): Boolean
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def
equals(arg0: Any): Boolean
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def
finalize(): Unit
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getClass(): Class[_]
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def
hashCode(): Int
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final
def
isInstanceOf[T0]: Boolean
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def
makeCancelable(f: (Listener[Unit]) ⇒ Unit, p: Listener[Unit]): Cancelable
- Attributes
- protected
- Definition Classes
- AsyncSemaphore → GenericSemaphore
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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
release(): Unit
Releases a permit, returning it to the pool.
Releases a permit, returning it to the pool.
If there are consumers waiting on permits being available, then the first in the queue will be selected and given a permit immediately.
- Annotations
- @UnsafeBecauseImpure()
- See also
withPermit, the preferred way to acquire and release
-
def
releaseN(n: Long): Unit
Releases
n
permits, potentially unblocking up ton
outstanding acquires.Releases
n
permits, potentially unblocking up ton
outstanding acquires.- n
number of permits to release - must be >= 0
- Annotations
- @UnsafeBecauseImpure()
- See also
withPermit, the preferred way to acquire and release
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
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def
toString(): String
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def
tryAcquire(): Boolean
Alias for
tryAcquireN(1)
.Alias for
tryAcquireN(1)
.The protocol is unsafe, because with the "try*" methods the user needs a firm grasp of what race conditions are and how they manifest and usage of such methods can lead to very fragile logic.
- Annotations
- @UnsafeProtocol() @UnsafeBecauseImpure()
- See also
tryAcquireN for the version that can acquire multiple permits
acquire for the version that can wait for acquisition
withPermit the preferred way to acquire and release
-
def
tryAcquireN(n: Long): Boolean
Acquires
n
permits now and returnstrue
, or returnsfalse
immediately.Acquires
n
permits now and returnstrue
, or returnsfalse
immediately. Error ifn < 0
.The protocol is unsafe, because with the "try*" methods the user needs a firm grasp of what race conditions are and how they manifest and usage of such methods can lead to very fragile logic.
- n
number of permits to acquire - must be >= 0
- Annotations
- @UnsafeProtocol() @UnsafeBecauseImpure()
- See also
tryAcquire for the alias that acquires a single permit
acquireN for the version that can wait for acquisition
withPermit, the preferred way to acquire and release
-
final
def
unsafeAcquireN(n: Long, await: Listener[Unit]): Cancelable
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- @tailrec()
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final
def
unsafeAsyncAcquireN(n: Long, await: Listener[Unit]): Cancelable
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final
def
unsafeAvailable(): Long
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final
def
unsafeAwaitAvailable(n: Long, await: Listener[Unit]): Cancelable
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final
def
unsafeCount(): Long
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final
def
unsafeReleaseN(n: Long): Unit
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- @tailrec()
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final
def
unsafeTryAcquireN(n: Long): Boolean
- Attributes
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- @tailrec()
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final
def
wait(): Unit
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final
def
wait(arg0: Long, arg1: Int): Unit
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final
def
wait(arg0: Long): Unit
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def
withPermit[A](f: () ⇒ Future[A]): CancelableFuture[A]
Returns a new future, ensuring that the given source acquires an available permit from the semaphore before it is executed.
Returns a new future, ensuring that the given source acquires an available permit from the semaphore before it is executed.
The returned future also takes care of resource handling, releasing its permit after being complete.
- f
is a function returning the
Future
instance we want to evaluate after we get the permit from the semaphore
- Annotations
- @UnsafeBecauseImpure()
-
def
withPermitN[A](n: Long)(f: () ⇒ Future[A]): CancelableFuture[A]
Returns a new future, ensuring that the given source acquires
n
available permits from the semaphore before it is executed.Returns a new future, ensuring that the given source acquires
n
available permits from the semaphore before it is executed.The returned future also takes care of resource handling, releasing its permits after being complete.
- n
is the number of permits required for the given function to be executed
- f
is a function returning the
Future
instance we want to evaluate after we get the permit from the semaphore
- Annotations
- @UnsafeBecauseImpure()