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/*
* Copyright 2017 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.firebase;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.firebase.internal.NonNull;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadFactory;
/**
* An interface that controls the thread pools and thread factories used by the Admin SDK. Each
* instance of {@link FirebaseApp} uses an implementation of this interface to create and manage
* threads.
*
* Multiple app instances may use the same ThreadManager instance.
* Methods in this interface may get invoked multiple times by the same
* app, during its lifetime. Apps may also invoke methods of this interface concurrently and
* so implementations should provide any synchronization necessary.
*/
public abstract class ThreadManager {
@NonNull
final FirebaseExecutors getFirebaseExecutors(@NonNull FirebaseApp app) {
return new FirebaseExecutors(getExecutor(app));
}
final void releaseFirebaseExecutors(
@NonNull FirebaseApp app, @NonNull FirebaseExecutors executor) {
releaseExecutor(app, executor.userExecutor);
}
/**
* Returns the main thread pool for an app. Implementations may return the same instance of
* ExecutorService for multiple apps. The returned thread pool is used for
* short-lived tasks by all components of an app.
*
*
For long-lived tasks (such as the ones started by the Realtime Database client), the SDK
* creates dedicated executors using the ThreadFactory returned by the
* {@link #getThreadFactory()} method.
*
* @param app A {@link FirebaseApp} instance.
* @return A non-null ExecutorService instance.
*/
@NonNull
protected abstract ExecutorService getExecutor(@NonNull FirebaseApp app);
/**
* Cleans up the thread pool associated with an app. This method is invoked when an app
* is deleted. This is guaranteed to be called with the ExecutorService previously
* returned by {@link #getExecutor(FirebaseApp)} for the corresponding app.
*
* @param app A {@link FirebaseApp} instance.
*/
protected abstract void releaseExecutor(
@NonNull FirebaseApp app, @NonNull ExecutorService executor);
/**
* Returns the ThreadFactory to be used for creating long-lived threads. This is
* used mainly to create the long-lived worker threads for the Realtime Database client, and
* other scheduled (periodic) tasks started by the SDK. The SDK guarantees
* clean termination of all threads started via this ThreadFactory, when the user
* calls {@link FirebaseApp#delete()}.
*
*
If long-lived threads cannot be supported in the current runtime, this method may
* throw a {@code RuntimeException}.
*
* @return A non-null ThreadFactory.
*/
@NonNull
protected abstract ThreadFactory getThreadFactory();
/**
* Wraps an ExecutorService in a ListeningExecutorService while keeping a reference to the
* original ExecutorService. This reference is used when it's time to release/cleanup the
* original ExecutorService.
*/
static final class FirebaseExecutors {
private final ExecutorService userExecutor;
private final ListeningExecutorService listeningExecutor;
private FirebaseExecutors(ExecutorService userExecutor) {
this.userExecutor = checkNotNull(userExecutor, "ExecutorService must not be null");
this.listeningExecutor = MoreExecutors.listeningDecorator(userExecutor);
}
ListeningExecutorService getListeningExecutor() {
return listeningExecutor;
}
}
}