RFR: 8087322: Implement a Semaphore utility class

[Kim Barrett]

On Jun 24, 2015, at 6:39 PM, David Holmes <david.holmes at oracle.com> wrote:
> 
>>> sem_trywait can also fail with EINTR.
>> 
>> Will fix the assert.
> 
> trywait can't fail with EINTR as it does not block - so nothing can be interrupted.

When dealing with standards like POSIX, I generally try to listen as
closely as I can to what the standard says, rather than trusting my
intuition about how something "ought" to work.  Compiler and library
authors are known for driving trucks through holes in one's intuition,
and then saying nyah, nyah to complaints.

So when POSIX says sem_trywait can return an error of EINTR and my
intuition says "no way", *I* still include the check. YMMV.

>>> src/os/windows/vm/os_windows.cpp
>>> 1905 WindowsSemaphore::~WindowsSemaphore() {
>>> 1906   if (_semaphore != NULL) {
>>> 1907     ::CloseHandle(_semaphore);
>>> 1908   }
>>> 
>>> I don't think the NULL check is needed here.
>> 
>> I'll remove it.
> 
> Not clear to me that we don't need it, and we do perform null checks elsewhere in the windows code.

We already have a NULL check in the constructor, and terminate if that fails.