//                               -*- Mode: C -*- 
// 
// Cforall Version 1.0.0 Copyright (C) 2022 University of Waterloo
// 
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// barrier.hfa -- simple barrier implemented using a monitor
// 
// Author           : Peter A. Buhr
// Created On       : Sun Nov 10 08:07:35 2024
// Last Modified By : Peter A. Buhr
// Last Modified On : Wed Nov 13 12:37:04 2024
// Update Count     : 9
// 

#pragma once

#include <monitor.hfa>

// Plan 9 inheritance does not work with monitors. Two monitor locks are created.

monitor barrier {
	unsigned int group, arrivals;						// group size, arrival counter
	condition c;										// wait for group to form
};

static inline void ?{}( barrier & b, unsigned int group ) {
	b.group = b.arrivals = group;						// arrivals count backward
}

// Returns a value indicating the reverse order the threads arrived, i.e. last thread returns 0 (and does not block)
// last is an optional hook that is called by the Gth thread before unblocking the other threads.
static inline unsigned int block( barrier & mutex b, fptr_t last = (fptr_t)0 ) with( b ) {
	arrivals -= 1;										// prefix decrement so last is 0 not 1
	unsigned arrived = b.arrivals;						// note arrival order
	if ( arrivals != 0 ) {								// wait for group to form
		wait( b.c );
	} else {											// group formed
		if ( last ) last();								// safe to call
		signal_all( c );								// unblock group
		arrivals = group;								// reset
	} // if
	return arrived;										// return arrival order
}