The Semaphore is an asynchronous semaphore implementation that
limits the parallelism on task execution.
The Semaphore is an asynchronous semaphore implementation that
limits the parallelism on task execution.
The following example instantiates a semaphore with a maximum parallelism of 10:
import cats.implicits._
import cats.effect.IO
// Needed for ContextShift[IO]
import monix.execution.Scheduler
implicit val cs = IO.contextShift(Scheduler.global)
// Dummies for didactic purposes
case class HttpRequest()
case class HttpResponse()
def makeRequest(r: HttpRequest): IO[HttpResponse] = IO(???)
for {
semaphore <- Semaphore[IO](provisioned = 10)
tasks = for (_ <- 0 until 1000) yield {
semaphore.withPermit(makeRequest(HttpRequest()))
}
// Execute in parallel; note that due to the `semaphore`
// no more than 10 tasks will be allowed to execute in parallel
_ <- tasks.toList.parSequence
} yield ()
==Credits==
Semaphore is now implementing cats.effect.Semaphore, deprecating
the old Monix TaskSemaphore.
The changes to the interface and some implementation details are inspired by the implementation in Cats-Effect, which was ported from FS2.
- Companion
- object
Value members
Concrete methods
Acquires a single permit. Alias for [[acquireN]](1).
Acquires a single permit. Alias for [[acquireN]](1).
- See also
withPermit, the preferred way to acquire and release
acquireN for a version that can acquire multiple permits
- Definition Classes
- Semaphore
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
a Semaphore[F] with 2 permits available, an acquireN(3) will
always be satisfied before a later call to acquireN(1).
- Value Params
- n
number of permits to acquire; must be >= 0
- See also
withPermit, the preferred way to acquire and release
acquire for a version acquires a single permit
Returns the number of permits currently available. Always non-negative.
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.
Returns a task that will be complete when the specified number of permits are available.
Returns a task that will be complete when the specified number of permits are available.
The protocol is unsafe because by the time the returned
task 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.
- Value Params
- n
is the number of permits waited on
Obtains a snapshot of the current count. Can be negative.
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.
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.
- See also
withPermit, the preferred way to acquire and release
- Definition Classes
- Semaphore
Releases n permits, potentially unblocking up to n
outstanding acquires.
Releases n permits, potentially unblocking up to n
outstanding acquires.
- Value Params
- n
number of permits to release - must be >= 0
- See also
withPermit, the preferred way to acquire and release
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.
- 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
- Definition Classes
- Semaphore
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.
- 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
Returns a new task, ensuring that the given source acquires an available permit from the semaphore before it is executed.
Returns a new task, ensuring that the given source acquires an available permit from the semaphore before it is executed.
The returned task also takes care of resource handling, releasing its permit after being complete.
- Value Params
- fa
is an effect to execute once the permit has been acquired; regardless of its result, the permit is released to the pool afterwards
Returns a new task, ensuring that the given source
acquires n available permits from the semaphore before
it is executed.
Returns a new task, ensuring that the given source
acquires n available permits from the semaphore before
it is executed.
The returned task also takes care of resource handling, releasing its permits after being complete.
- Value Params
- fa
is an effect to execute once the permits have been acquired; regardless of its result, the permits are released to the pool afterwards
- n
is the number of permits required for the given function to be executed