2013/10/25 Andrey Semashev
T * expected1 = 0; T * expected2 = 0; if ( ! a[index].compare_exchange_strong( expected1, expected2) ) { // expected1 is not NULL, expected1 removed == a[index] contains NULL }
No, that's not right. If compare_exchange_strong returns false, the operation have failed and a[index] != NULL (at least, that's how compare_exchange_strong have left it). It should be:
T* expected = a[index].load(memory_order_acquire); while (!a[index].compare_exchange_weak(expected, NULL, memory_order_release, memory_order_acquire)) { }
if (expected) // The expected value was removed from the array else // The array element was removed by some other thread
agreed - but shouldn't we use strong memory-order (I remember that Herb S. recommended to use memory_order_strong in one of its sessions)