CountDownLatch完整源码(基于JDK1.7.0_40)
1
24
25
35
36 package java.util.concurrent;
37 import java.util.concurrent.locks.*;
38 import java.util.concurrent.atomic.*;
39
40
161 public class CountDownLatch {
162
166 private static final class Sync extends AbstractQueuedSynchronizer {
167 private static final long serialVersionUID = 4982264981922014374L;
168
169 Sync(int count) {
170 setState(count);
171 }
172
173 int getCount() {
174 return getState();
175 }
176
177 protected int tryAcquireShared(int acquires) {
178 return (getState() == 0) ? 1 : -1;
179 }
180
181 protected boolean tryReleaseShared(int releases) {
182 // Decrement count; signal when transition to zero
183 for (;;) {
184 int c = getState();
185 if (c == 0)
186 return false;
187 int nextc = c-1;
188 if (compareAndSetState(c, nextc))
189 return nextc == 0;
190 }
191 }
192 }
193
194 private final Sync sync;
195
196
203 public CountDownLatch(int count) {
204 if (count < 0) throw new IllegalArgumentException("count < 0");
205 this.sync = new Sync(count);
206 }
207
208
235 public void await() throws InterruptedException {
236 sync.acquireSharedInterruptibly(1);
237 }
238
239
280 public boolean await(long timeout, TimeUnit unit)
281 throws InterruptedException {
282 return sync.tryAcquireSharedNanos(1, unit.tonanos(timeout));
283 }
284
285
295 public void countDown() {
296 sync.releaseShared(1);
297 }
298
299
306 public long getCount() {
307 return sync.getCount();
308 }
309
310
317 public String toString() {
318 return super.toString() + "[Count = " + sync.getCount() + "]";
319 }
320 }
CountDownLatch是通过“共享锁”实现的。下面，我们分析CountDownLatch中3个核心函数: CountDownLatch(int count), await(), countDown()。
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