スレッドの優先度について調べた ref: http://qiita.com/amay077/items/c2f7db34976e8d2a16ac

file0.java

// 指定した Priority の ThreadFactory を生成して返す
private ThreadFactory makeThreadFactory(final int priority) {
    return new ThreadFactory() {

        @Override
        public Thread newThread(Runnable r) {
            Thread thread = new Thread(r);
            thread.setPriority(priority);
            return thread;
        }
    };
}

// 使ってみる
private void testExecutor() {
    final ExecutorService executor = 
        Executors.newSingleThreadExecutor(makeThreadFactory(Thread.MIN_PRIORITY));

    executor.submit(new Runnable() {
        @Override
        public void run() {
            // なにかの処理
        }
    });
}

file1.java

private ThreadFactory makeThreadFactory(final int priority) {
    // 上と同じなので省略
}

// タスクを生成する
private Runnable makeTask(final String tag, final StringBuffer buffer, 
        final CountDownLatch latch) {
    return new Runnable() {
        @Override
        public void run() {
            // タスクが開始された時に、A or B or C を追加してく
            buffer.append(tag); // StringBuffer は Thread-safe なハズだ

            // Wait
            for (int j = 0; j < 1000000; j++) { } 

            latch.countDown();
        }
    };
}

// 検証実行
public void testThreadPriority() throws InterruptedException {
    // MIN, NORMAL, MAX な Priority の Executor を生成
    final ExecutorService minExecutor = 
            Executors.newSingleThreadExecutor(makeThreadFactory(Thread.MIN_PRIORITY));
    final ExecutorService norExecutor = 
            Executors.newSingleThreadExecutor(makeThreadFactory(Thread.NORM_PRIORITY));
    final ExecutorService maxExecutor = 
            Executors.newSingleThreadExecutor(makeThreadFactory(Thread.MAX_PRIORITY));

    final CountDownLatch latch = new CountDownLatch(100 * 3);
    final StringBuffer builder = new StringBuffer();

    // それぞれの Executor にじゃんじゃんタスクを投入
    for (int i = 0; i < 100; i++) {
        minExecutor.submit(makeTask("C", builder, latch)); // MIN->"C"
        norExecutor.submit(makeTask("B", builder, latch)); // NORMAL->"B"
        maxExecutor.submit(makeTask("A", builder, latch)); // MAX->"A"
    }

    // 全部のタスクが終わるのを待つ
    latch.await();
    Log.d(TAG, builder.toString()); // タスクが処理された順番を出力
}