MCS.h

#pragma once

#include <stdbool.h>

typedef struct mcs_node {
	#ifndef ATOMIC
	struct mcs_node * volatile next;
	#else
	_Atomic(struct mcs_node *) next;
	#endif // ! ATOMIC
	VTYPE spin;
} MCS_node CALIGN;

#ifndef ATOMIC
typedef MCS_node * MCS_lock;
#else
typedef _Atomic(MCS_node *) MCS_lock;
#endif // ! ATOMIC

static inline void mcs_lock( MCS_lock * lock, MCS_node * node ) {
	node->next = NULL;

#ifndef MCS_OPT1										// default option
	node->spin = true;									// alternative position and remove fence below
	WO( Fence(); ); // 1
#endif // MCS_OPT1

	MCS_node * prev = Fas( *lock, node );

  if ( SLOWPATH( prev == NULL ) ) return;				// no one on list ?

#ifdef MCS_OPT1
	node->spin = true;									// mark as waiting
	WO( Fence(); ); // 2
#endif // MCS_OPT1

	prev->next = node;									// add to list of waiting threads
	WO( Fence(); ); // 3

	#ifndef MPAUSE
	while ( node->spin == true ) Pause();				// busy wait on my spin variable
	#else
	MPause( node->spin, == true );						// busy wait on my spin variable
	#endif // MPAUSE
	WO( Fence(); ); // 4
} // mcs_lock

static inline void mcs_unlock( MCS_lock * lock, MCS_node * node ) {
	WO( Fence(); ); // 5
#ifdef MCS_OPT2											// original, default option
	if ( FASTPATH( node->next == NULL ) ) {				// no one waiting ?

  if ( SLOWPATH( Cas( *lock, node, NULL ) ) ) return;	// Fence

		#ifndef MPAUSE
		while ( node->next == NULL ) Pause();			// busy wait until my node is modified
		#else
		MPause( node->next, == NULL );					// busy wait until my node is modified
		#endif // MPAUSE
	} // if

	WO( Fence(); ); // 6
	node->next->spin = false;							// stop their busy wait
#else													// Scott book Figure 4.8
	MCS_node * succ = node->next;
	if ( FASTPATH( succ == NULL ) ) {					// no one waiting ?
		// node is potentially at the tail of the MCS chain

  if ( SLOWPATH( Cas( *lock, node, NULL ) ) ) return;	// Fence
		// Either a new thread arrived in the LD-CAS window above or fetched a false NULL
		// as the successor has yet to store into node->next.

		#ifndef MPAUSE
		while ( (succ = node->next) == NULL ) Pause();	// busy wait until my node is modified
		#else
		MPauseS( succ =, node->next, == NULL );			// busy wait until my node is modified
		#endif // MPAUSE
	} // if

	WO( Fence(); ); // 7
	succ->spin = false;
#endif // MCS_OPT2
} // mcs_unlock

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