base/android/java/src/org/chromium/base/task/SingleThreadTaskRunnerImpl.java

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package org.chromium.base.task;

import android.os.Handler;
import android.support.annotation.Nullable;

import org.chromium.base.annotations.JNINamespace;

/**
 * Implementation of the abstract class {@link SingleThreadTaskRunner}. Before native initialization
 * tasks are posted to the {@link java android.os.Handler}, after native initialization they're
 * posted to a base::SingleThreadTaskRunner which runs on the same thread.
 */
@JNINamespace("base")
public class SingleThreadTaskRunnerImpl extends TaskRunnerImpl implements SingleThreadTaskRunner {
    @Nullable
    private final Handler mHandler;

    /**
     * @param handler The backing Handler if any. Note this must run tasks on the same thread that
     * the native code runs a task with |traits|.  If handler is null then tasks won't run until
     * native has initialized.
     * @param traits The TaskTraits associated with this SingleThreadTaskRunnerImpl.
     */
    public SingleThreadTaskRunnerImpl(Handler handler, TaskTraits traits) {
        super(traits, "SingleThreadTaskRunnerImpl");
        mHandler = handler;
    }

    @Override
    public boolean belongsToCurrentThread() {
        if (mNativeTaskRunnerAndroid != 0)
            return nativeBelongsToCurrentThread(mNativeTaskRunnerAndroid);
        if (mHandler != null) return mHandler.getLooper().getThread() == Thread.currentThread();
        assert (false);
        return false;
    }

    @Override
    protected void schedulePreNativeTask() {
        // if |mHandler| is null then pre-native task execution is not supported.
        if (mHandler != null) mHandler.post(mRunPreNativeTaskClosure);
    }

    private native boolean nativeBelongsToCurrentThread(long nativeTaskRunnerAndroid);
}