Class SharedResourceHolder

java.lang.Object

io.grpc.internal.SharedResourceHolder

@ThreadSafe
public final class SharedResourceHolder
extends Object

A holder for shared resource singletons.

Components like client channels and servers need certain resources, e.g. a thread pool, to run. If the user has not provided such resources, these components will use a default one, which is shared as a static resource. This class holds these default resources and manages their life-cycles.

A resource is identified by the reference of a SharedResourceHolder.Resource object, which is typically a singleton, provided to the get() and release() methods. Each Resource object (not its class) maps to an object cached in the holder.

Resources are ref-counted and shut down after a delay when the ref-count reaches zero.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	SharedResourceHolder.Instance
static interface	SharedResourceHolder.Resource<T>	Defines a resource, and the way to create and destroy instances of it.
(package private) static interface	SharedResourceHolder.ScheduledExecutorFactory

Field Summary

Fields

Modifier and Type	Field	Description
(package private) static final long	DESTROY_DELAY_SECONDS
private ScheduledExecutorService	destroyer
private final SharedResourceHolder.ScheduledExecutorFactory	destroyerFactory
private static final SharedResourceHolder	holder
private final IdentityHashMap<SharedResourceHolder.Resource<?>, SharedResourceHolder.Instance>	instances

Constructor Summary

Constructors

Constructor	Description
SharedResourceHolder(SharedResourceHolder.ScheduledExecutorFactory destroyerFactory)

Method Summary

Modifier and Type	Method	Description
static <T> T	get(SharedResourceHolder.Resource<T> resource)	Try to get an existing instance of the given resource.
(package private) <T> T	getInternal(SharedResourceHolder.Resource<T> resource)	Visible to unit tests.
static <T> T	release(SharedResourceHolder.Resource<T> resource, T instance)	Releases an instance of the given resource.
(package private) <T> T	releaseInternal(SharedResourceHolder.Resource<T> resource, T instance)	Visible to unit tests.

Methods inherited from class Object

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

Field Details

DESTROY_DELAY_SECONDS

static final long DESTROY_DELAY_SECONDS

See Also:

• Constant Field Values

holder

private static final SharedResourceHolder holder

instances

private final IdentityHashMap<SharedResourceHolder.Resource<?>, SharedResourceHolder.Instance> instances

destroyerFactory

private final SharedResourceHolder.ScheduledExecutorFactory destroyerFactory

destroyer

private ScheduledExecutorService destroyer

Constructor Details

SharedResourceHolder

SharedResourceHolder(SharedResourceHolder.ScheduledExecutorFactory destroyerFactory)

Method Details

get

public static <T> T get(SharedResourceHolder.Resource<T> resource)

Try to get an existing instance of the given resource. If an instance does not exist, create a new one with the given factory.

Parameters:

resource - the singleton object that identifies the requested static resource

release

public static <T> T release(SharedResourceHolder.Resource<T> resource,
 T instance)

Releases an instance of the given resource.

The instance must have been obtained from get(Resource). Otherwise will throw IllegalArgumentException.

Caller must not release a reference more than once. It's advisory that you clear the reference to the instance with the null returned by this method.

Parameters:

resource - the singleton Resource object that identifies the released static resource

instance - the released static resource

Returns:

a null which the caller can use to clear the reference to that instance.

getInternal

<T> T getInternal(SharedResourceHolder.Resource<T> resource)

Visible to unit tests.

See Also:

• get(Resource)

releaseInternal

<T> T releaseInternal(SharedResourceHolder.Resource<T> resource,
 T instance)

Visible to unit tests.