On Mon, 2007-10-29 at 10:37 +0100, Samuel Tardieu wrote: > >>>>> "skaller" == skaller <[EMAIL PROTECTED]> writes:
> with (x86): > > movl a, %eax > cmpl $1, 4(%esp) > sbbl $-1, %eax > movl %eax, a > > There is clearly a race condition if you have multiple threads > executing this code even if only one thread has "locked" being true. Ah .. ok I think I finally see. Thanks! The code ensures well definedness by checking the establishment of the required invariant and dynamically chosing whether or not to do the access on that basis .. and the optimisation above defeats that by lifting the access out of the conditional. In the single threaded case the lift works because it relies on sequential access, which is the only possibility for a single thread. -- John Skaller <skaller at users dot sf dot net> Felix, successor to C++: http://felix.sf.net
