Java performance issue with Thread.sleep()

Question

Inline Java IDE hint states, "Invoking Thread.sleep in loop can cause performance problems." I can find no elucidation elsewhere in the docs re. this statement.

Why? How? What other method might there be to delay execution of a thread?

Answer 1

It is not that Thread.sleep in a loop itself is a performance problem, but it is usually a hint that you are doing something wrong.

while(! goodToGoOnNow()) {    Thread.sleep(1000); } 

Use Thread.sleep only if you want to suspend your thread for a certain amount of time. Do not use it if you want to wait for a certain condition.

For this situation, you should use wait/notify instead or some of the constructs in the concurrency utils packages.

Polling with Thread.sleep should be used only when waiting for conditions external to the current JVM (for example waiting until another process has written a file).

Answer 2

It depends on whether the wait is dependent on another thread completing work, in which case you should use guarded blocks, or high level concurrency classes introduced in Java 1.6. I recently had to fix some CircularByteBuffer code that used Thread sleeps instead of guarded blocks. With the previous method, there was no way to ensure proper concurrency. If you just want the thread to sleep as a game might, in the core game loop to pause execution for a certain amount of time so that over threads have good period in which to execute, Thread.sleep(..) is perfectly fine.