The Java Language Specification, Third Edition

THREADS AND LOCKS Sleep and Yield 17.9
17.9 Sleep and Yield
Thread.sleep causes the currently executing thread to sleep (temporarily
cease execution) for the specified duration, subject to the precision and accuracy
of system timers and schedulers. The thread does not lose ownership of any monitors,
and resumption of execution will depend on scheduling and the availability
of processors on which to execute the thread.
Neither a sleep for a period of zero time nor a yield operation need have
observable effects.
It is important to note that neither Thread.sleep nor Thread.yield have
any synchronization semantics. In particular, the compiler does not have to flush
writes cached in registers out to shared memory before a call to Thread.sleep or
Thread.yield, nor does the compiler have to reload values cached in registers
after a call to Thread.sleep or Thread.yield.
DISCUSSION
For example, in the following (broken) code fragment, assume that this.done is a non-volatile
boolean field:
while (!this.done)
Thread.sleep(1000);
The compiler is free to read the field this.done just once, and reuse the cached value
in each execution of the loop. This would mean that the loop would never terminate, even if
another thread changed the value of this.done.
DRAFT
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