US 63-131 33.9.3.3 [thread.barrier.class] Thread for running completion function

[wg21bot]

barrier is over-constrained, requiring implementations to run the CompletionFunction on the last thread that arrives at the barrier during the phase. This prevents barrier from benefiting from hardware acceleration for thread synchronization on certain platforms.

Proposed change:

Adopt P2588, which relaxes barrier’s phase completion guarantees.

[brycelelbach]

The proposed resolution is to adopt P2588 https://github.com/cplusplus/papers/issues/1246

[jensmaurer]

Accepted.