1 /*
2  * Copyright (C) 2018 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.bips.util;
18 
19 import java.util.ArrayList;
20 import java.util.Collections;
21 import java.util.List;
22 
23 /**
24  * A lock that always allows higher-priority attempts to receive the lock first
25  */
26 public class PriorityLock {
27     private boolean mLocked = false;
28     private List<Integer> mPriorities = new ArrayList<>();
29 
30     /**
31      * Return when locked, always giving priority to the highest priority lock request
32      */
lock(int priority)33     public synchronized void lock(int priority) throws InterruptedException {
34         if (mLocked) {
35             mPriorities.add(priority);
36             Collections.sort(mPriorities);
37             try {
38                 while (mLocked || priority < mPriorities.get(mPriorities.size() - 1)) {
39                     wait();
40                 }
41             } finally {
42                 mPriorities.remove((Integer) priority);
43             }
44         }
45         mLocked = true;
46     }
47 
48     /**
49      * Unlock this object (when it is already locked)
50      */
unlock()51     public synchronized void unlock() {
52         if (!mLocked) {
53             throw new IllegalArgumentException("not locked");
54         }
55         mLocked = false;
56         notifyAll();
57     }
58 }
59