src/base/android/java/src/org/chromium/base/task/SerialExecutor.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 java.util.ArrayDeque;
import java.util.concurrent.Executor;

class SerialExecutor implements Executor {
    final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
    Runnable mActive;

    @Override
    public synchronized void execute(final Runnable r) {
        mTasks.offer(new Runnable() {
            @Override
            public void run() {
                try {
                    r.run();
                } finally {
                    scheduleNext();
                }
            }
        });
        if (mActive == null) {
            scheduleNext();
        }
    }

    protected synchronized void scheduleNext() {
        if ((mActive = mTasks.poll()) != null) {
            AsyncTask.THREAD_POOL_EXECUTOR.execute(mActive);
        }
    }
}