BarrierConsumer.java revision 32b3062031c2853b08da65378af629f2964621bd 
1/*
2 * Copyright (C) 2010 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
17package com.android.quicksearchbox.util;
18
19import java.util.ArrayList;
20import java.util.concurrent.locks.Condition;
21import java.util.concurrent.locks.Lock;
22import java.util.concurrent.locks.ReentrantLock;
23
24/**
25 * A consumer that consumes a fixed number of values. When the expected number of values
26 * has been consumed, further values are rejected.
27 */
28public class BarrierConsumer<A> implements Consumer<A> {
29
30    private final Lock mLock = new ReentrantLock();
31    private final Condition mNotFull = mLock.newCondition();
32
33    private final int mExpectedCount;
34
35    // Set to null when getValues() returns.
36    private ArrayList<A> mValues;
37
38    /**
39     * Constructs a new BarrierConsumer.
40     *
41     * @param expectedCount The number of values to consume.
42     */
43    public BarrierConsumer(int expectedCount) {
44        mExpectedCount = expectedCount;
45        mValues = new ArrayList<A>(expectedCount);
46    }
47
48    /**
49     * Blocks until the expected number of results is available, or until the thread is
50     * interrupted. This method should not be called multiple times.
51     *
52     * @return A list of values, never {@code null}.
53     */
54    public ArrayList<A> getValues() {
55        mLock.lock();
56        try {
57            try {
58                while (!isFull()) {
59                    mNotFull.await();
60                }
61            } catch (InterruptedException ex) {
62                // Return the values that we've gotten so far
63            }
64            ArrayList<A> values = mValues;
65            mValues = null;  // mark that getValues() has returned
66            return values;
67        } finally {
68            mLock.unlock();
69        }
70    }
71
72    public boolean consume(A value) {
73        mLock.lock();
74        try {
75            // Do nothing if getValues() has alrady returned,
76            // or enough values have already been consumed
77            if (mValues == null || isFull()) {
78                return false;
79            }
80            mValues.add(value);
81            if (isFull()) {
82                // Wake up any thread waiting in getValues()
83                mNotFull.signal();
84            }
85            return true;
86        } finally {
87            mLock.unlock();
88        }
89    }
90
91    private boolean isFull() {
92        return mValues.size() == mExpectedCount;
93    }
94}
95