[cpp-threads] Yet another visibility question

[Peter Dimov]

Let me re-ask the same question again using slightly different wording. I'm 
really not sure of the correct answer. "Correct" as in both "follows from 
the memory model", and "what we want".

// x y z initially zero

// thread 1

x = 1;
fetchadd_release( &z, +1 );

// thread 2

y = 1;
fetchadd_release( &z, +1 );

// thread 3

if( load_acquire( &z ) == 2 )
{
    assert( x == 1 && y == 1 );
}

Will the assert pass?

In other words, does the load-acquire from z in thread 3 introduce sync-with 
edges to all previous store-releases to z, or just to the last one?