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Posted to dev@dubbo.apache.org by GitBox <gi...@apache.org> on 2018/04/21 05:50:14 UTC
[GitHub] chickenlj commented on issue #1634: 为什么要在AbstractMonitorFactory#getMonitor这个地方要用上锁
chickenlj commented on issue #1634: 为什么要在AbstractMonitorFactory#getMonitor这个地方要用上锁
URL: https://github.com/apache/incubator-dubbo/issues/1634#issuecomment-383270026
I think you should look at this `LOCK` as a whole, we have null check before entering this lock:
```java
Monitor monitor = MONITORS.get(key);
Future<Monitor> future = FUTURES.get(key);
if (monitor != null || future != null) {
return monitor;
}
LOCK.lock();
try {
monitor = MONITORS.get(key);
future = FUTURES.get(key);
if (monitor != null || future != null) {
return monitor;
}
final URL monitorUrl = url;
final ListenableFutureTask<Monitor> listenableFutureTask = ListenableFutureTask.create(new MonitorCreator(monitorUrl));
listenableFutureTask.addListener(new MonitorListener(key));
executor.execute(listenableFutureTask);
FUTURES.put(key, listenableFutureTask);
return null;
} finally {
// unlock
LOCK.unlock();
}
```
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