Richard Frith-Macdonald <[EMAIL PROTECTED]> writes:
> - (id) sharedInstance
> {
> static volatile uint8_t isCreated = 0; // single byte
> declared volatile so we read from memory rather than a register
> static volatile id theInstance = nil;
>
> if (isCreated == 0)
> {
> [theLock lock];
> if (isCreated == 0 && theInstance == nil)
> {
> theInstance = [theClass new];
> }
> [theLock unlock];
> isCreated = 1;
> }
> return theInstance;
> }
I am not sure this is safe on a multiprocessor machine
Becauses I think that on a multiprocessor machine the following might happen:
Thread A on Processor A creates the instance and continues
Thread B on Processor B sees isCreated = 1, but still has a stale
value (nil) for 'theInstance' in its L1/L2 memory cache
and returns the nil.
But I don't know enough about the memory model that the current
processors use and how that interacts with locking.
Wim Oudshoorn.
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