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This article mainly explains the "countdown timer CountDownLatch example analysis", the article explains the content is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in depth, together to study and learn "countdown timer CountDownLatch example analysis" bar!

CountDownLatch, or countdown timer, is a very useful tool class in multithreaded concurrency control. It can control threads to wait until the countdown timer returns to zero.

To give you a question, control 5 threads after the execution of the main line and then go down to execute, and count the time spent by 5 threads. Of course we can do this in the form of join, but what if I say count 1000 threads? Do you have to write 1000 join waits? This is obviously unrealistic.

To cut the crap, let's give an example to see how the above question is implemented and understand the countdown timer.

First of all, the number of countdown timers is agreed through new CountDownLatch (5), which in this case is the number of threads, and then the countdown timer-1 is set after each thread has finished executing. The countDown () method is the countdown timer-1, which needs to be placed in the finally and must be released in each thread, otherwise if the child thread reports an error that the countdown timer will never clear 0 for some reason, the lead thread will wait.

The await () method is that the main thread blocks and waits for the countdown to return to zero before continuing to execute. Of course, await can take time to go in, regardless of whether the countdown timer returns to zero or not.

As shown in the example above, we output the last number 0 of the countdown timer, indicating that the countdown timer is back to zero, as well as the time spent from start to finish. From this example, we can fully understand the meaning of the countdown timer, this tool class is often useful and easy to use in actual development.

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