/**
* Visible to unit tests.
*
* @see #get(Resource)
*/
@SuppressWarnings("unchecked")
synchronized <T> T getInternal(Resource<T> resource) {
Instance instance = instances.get(resource);
if (instance == null) {
instance = new Instance(resource.create());
instances.put(resource, instance);
}
if (instance.destroyTask != null) {
instance.destroyTask.cancel(false);
instance.destroyTask = null;
}
instance.refcount++;
return (T) instance.payload;
}
/** Visible to unit tests. */
synchronized <T> T releaseInternal(final Resource<T> resource, final T instance) {
final Instance cached = instances.get(resource);
if (cached == null) {
throw new IllegalArgumentException("No cached instance found for " + resource);
}
Preconditions.checkArgument(instance == cached.payload, "Releasing the wrong instance");
Preconditions.checkState(cached.refcount > 0, "Refcount has already reached zero");
cached.refcount--;
if (cached.refcount == 0) {
Preconditions.checkState(cached.destroyTask == null, "Destroy task already scheduled");
// Schedule a delayed task to destroy the resource.
if (destroyer == null) {
destroyer = destroyerFactory.createScheduledExecutor();
}
cached.destroyTask =
destroyer.schedule(
new LogExceptionRunnable(
new Runnable() {
@Override
public void run() {
synchronized (SharedResourceHolder.this) {
// Refcount may have gone up since the task was scheduled. Re-check it.
if (cached.refcount == 0) {
resource.close(instance);
instances.remove(resource);
if (instances.isEmpty()) {
destroyer.shutdown();
destroyer = null;
}
}
}
}
}),
DESTROY_DELAY_SECONDS,
TimeUnit.SECONDS);
}
// Always returning null
return null;
}