If you are going to hold the lock on the collection during an entire iteration, then other threads may be stalled waiting for the collection lock for a long time.
如果您要在整个迭代期间都保持对集合的锁，那么其他的线程就会在锁外停留很长的一段时间，等待解锁。
The race conditions illustrated in Listing 1 often make it necessary to hold the single collection lock for much longer than it takes to execute a single operation.
清单1中演示的争用条件常常使得对单个集合的锁在单个操作执行完毕之后还必须继续保持一段较长的时间。
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