pfq-rwlock.h

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//******************************************************************************
//
// File:
//   $HeadURL$
//
// Purpose:
//   Define the API for a fair, phased reader-writer lock with local spinning
//
// Reference:
//   Björn B. Brandenburg and James H. Anderson. 2010. Spin-based reader-writer
//   synchronization for multiprocessor real-time systems. Real-Time Systems
//   46(1):25-87 (September 2010).  http://dx.doi.org/10.1007/s11241-010-9097-2
//
// Notes:
//   the reference uses a queue for arriving readers. on a cache coherent
//   machine, the local spinning property for waiting readers can be achieved
//   by simply using a cacheble flag. the implementation here uses that
//   simplification.
//
//******************************************************************************

#ifndef __pfq_rwlock_h__
#define __pfq_rwlock_h__



//******************************************************************************
// global includes
//******************************************************************************

#include <inttypes.h>
#include <stdbool.h>



//******************************************************************************
// local includes
//******************************************************************************

#include "mcs-lock.h"


//******************************************************************************
// macros
//******************************************************************************

// align a variable at the start of a cache line
#define cache_aligned __attribute__((aligned(128)))



//******************************************************************************
// types
//******************************************************************************

typedef mcs_node_t pfq_rwlock_node_t;

typedef struct bigbool {
  atomic_bool bit cache_aligned;
} bigbool;

typedef struct {
  //----------------------------------------------------------------------------
  // reader management
  //----------------------------------------------------------------------------
  atomic_uint_least32_t rin cache_aligned;  // = 0
  atomic_uint_least32_t rout cache_aligned;  // = 0
  atomic_uint_least32_t last cache_aligned;  // = WRITER_PRESENT
  bigbool writer_blocking_readers[2]; // false

  //----------------------------------------------------------------------------
  // writer management
  //----------------------------------------------------------------------------
  mcs_lock_t wtail cache_aligned;  // init
  mcs_node_t *whead cache_aligned;  // null

} pfq_rwlock_t;



//******************************************************************************
// interface operations
//******************************************************************************

void pfq_rwlock_init(pfq_rwlock_t *l);

void pfq_rwlock_read_lock(pfq_rwlock_t *l);

void pfq_rwlock_read_unlock(pfq_rwlock_t *l);

void pfq_rwlock_write_lock(pfq_rwlock_t *l, pfq_rwlock_node_t *me);

void pfq_rwlock_write_unlock(pfq_rwlock_t *l, pfq_rwlock_node_t *me);

#endif