[SOLR-11782] LatchWatcher.await doesn’t protect against spurious wakeup

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 7.3, 8.0
• Assignee: Tomas Eduardo Fernandez Lobbe
• Reporter: Tomas Eduardo Fernandez Lobbe
• Created: 20/Dec/17 01:56
• Updated: 02/Oct/19 17:30
• Resolved: 30/Jan/18 22:36

Description

I noticed that LatchWatcher.await does:

public void await(long timeout) throws InterruptedException {
      synchronized (lock) {
        if (this.event != null) return;
        lock.wait(timeout);
      }
    }

while the recommendation of lock.wait is to check the wait condition even after the method returns in case of spurious wakeup. lock is a private local field to which notifyAll is called only after a zk event is being handled. I think we should check the await method to something like:

public void await(long timeout) throws InterruptedException {
      assert timeout > 0;
      long timeoutTime = System.currentTimeMillis() + timeout;
      synchronized (lock) {
        while (this.event == null) {
          long nextTimeout = timeoutTime - System.currentTimeMillis();
          if (nextTimeout <= 0) {
            return;
          }
          lock.wait(nextTimeout);
        }
      }
    }