org.janusgraph.diskstorage.util.backpressure

Class SemaphoreQueryBackPressure

java.lang.Object

java.util.concurrent.Semaphore

org.janusgraph.diskstorage.util.backpressure.SemaphoreQueryBackPressure

All Implemented Interfaces:

Serializable, QueryBackPressure

public class SemaphoreQueryBackPressure
extends Semaphore
implements QueryBackPressure

Query back pressure implementation which uses Semaphore to control back pressure.
Warning: This implementation assumes that for each `acquireBeforeQuery` call there will be exactly one `releaseAfterQuery` call. This implementation uses `backPressureLimit` as a starting `permits` amount of the Semaphore. Each time `releaseAfterQuery` is called it will add a new `permit` even if the current total amount of permits is already grater then `backPressureLimit`. In case you assume that the logic where `SemaphoreQueryBackPressure` is used might be affected by any bug which may call `releaseAfterQuery` more than once for a single `acquireBeforeQuery` call then it's suggested to use SemaphoreProtectedReleaseQueryBackPressure which has a tiny overhead for `releaseAfterQuery` calls but protects those calls from the possible side effects of calling `releaseAfterQuery` more than once for any `acquireBeforeQuery` call.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SemaphoreQueryBackPressure(int backPressureLimit)

Method Summary

Modifier and Type	Method and Description
void	acquireBeforeQuery() Acquires one slot.
void	close() Releases any resources related to the back pressure mechanism.
void	releaseAfterQuery() Releases one slot in non-blocking fashion.

Methods inherited from class java.util.concurrent.Semaphore

acquire, acquire, acquireUninterruptibly, acquireUninterruptibly, availablePermits, drainPermits, getQueuedThreads, getQueueLength, hasQueuedThreads, isFair, reducePermits, release, release, toString, tryAcquire, tryAcquire, tryAcquire, tryAcquire

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

SemaphoreQueryBackPressure

public SemaphoreQueryBackPressure(int backPressureLimit)

Method Detail

acquireBeforeQuery

public void acquireBeforeQuery()

Description copied from interface: QueryBackPressure

Acquires one slot. If not slots are available then this method will be blocked until a slot is available.

Specified by:

acquireBeforeQuery in interface QueryBackPressure

releaseAfterQuery

public void releaseAfterQuery()

Description copied from interface: QueryBackPressure

Releases one slot in non-blocking fashion. The successful execution of this method doesn't mean that the release is happened. Instead, execution of this method guarantees that the release will happen.

Specified by:

releaseAfterQuery in interface QueryBackPressure

close

public void close()

Description copied from interface: QueryBackPressure

Releases any resources related to the back pressure mechanism. Makes this instance unusable after that.

Specified by:

close in interface QueryBackPressure