PtrLock.h

Go to the documentation of this file.

#ifndef GALOIS_RUNTIME_LL_PTRLOCK_H
#define GALOIS_RUNTIME_LL_PTRLOCK_H

#include "Galois/config.h"
#include "Galois/Runtime/ll/CompilerSpecific.h"

#include <stdint.h>
#include <cassert>
#include GALOIS_CXX11_STD_HEADER(atomic)

namespace Galois {
namespace Runtime {
namespace LL {

template<typename T, bool isALock>
class PtrLock;

template<typename T>
class PtrLock<T, true> {
  std::atomic<uintptr_t> _lock;

  GALOIS_ATTRIBUTE_NOINLINE
  void slow_lock() {
    uintptr_t oldval;
    do {
      while ((_lock.load(std::memory_order_acquire) & 1) != 0) {
        asmPause();
      }
      oldval = _lock.fetch_or(1, std::memory_order_acq_rel);
    } while (oldval & 1);
    assert(_lock);
  }

public:
  PtrLock() : _lock(0) {}
  //relaxed order for copy
  PtrLock(const PtrLock& p) : _lock(p._lock.load(std::memory_order_relaxed)) {}

  PtrLock& operator=(const PtrLock& p) {
    if (&p == this) return *this;
    //relaxed order for initialization
    _lock.store(p._lock.load(std::memory_order_relaxed), std::memory_order_relaxed);
    return *this;
  }

  inline void lock() {
    uintptr_t oldval = _lock.load(std::memory_order_relaxed);
    if (oldval & 1)
      goto slow_path;
    if (!_lock.compare_exchange_weak(oldval, oldval | 1, std::memory_order_acq_rel, std::memory_order_relaxed))
      goto slow_path;
    assert(is_locked());
    return;

  slow_path:
    slow_lock();
  }

  inline void unlock() {
    assert(is_locked());
    _lock.store(_lock.load(std::memory_order_relaxed) & ~(uintptr_t)1, std::memory_order_release);
  }

  inline void unlock_and_clear() {
    assert(is_locked());
    _lock.store(0, std::memory_order_release);
  }

  inline void unlock_and_set(T* val) {
    assert(is_locked());
    assert(!((uintptr_t)val & 1));
    _lock.store((uintptr_t) val, std::memory_order_release);
  }
  
  inline T* getValue() const {
    return (T*)(_lock.load(std::memory_order_relaxed) & ~(uintptr_t)1);
  }

  inline void setValue(T* val) {
    uintptr_t nval = (uintptr_t)val;
    nval |= (_lock & 1);
    //relaxed OK since this doesn't clear lock
    _lock.store(nval, std::memory_order_relaxed);
  }

  inline bool try_lock() {
    uintptr_t oldval = _lock.load(std::memory_order_relaxed);
    if ((oldval & 1) != 0)
      return false;
    oldval = _lock.fetch_or(1, std::memory_order_acq_rel);
    return !(oldval & 1);
  }

  inline bool is_locked() const {
    return _lock.load(std::memory_order_acquire) & 1;
  }

  inline bool CAS(T* oldval, T* newval) {
    assert(!((uintptr_t)oldval & 1) && !((uintptr_t)newval & 1));
    uintptr_t old = (uintptr_t)oldval;
    return _lock.compare_exchange_strong(old, (uintptr_t)newval);
  }

  inline bool stealing_CAS(T* oldval, T* newval) {
    uintptr_t old = 1 | (uintptr_t)oldval;
    return _lock.compare_exchange_strong(old, 1 | (uintptr_t)newval);
  }
};

template<typename T>
class PtrLock<T, false> {
  T* _lock;
public:
  PtrLock() : _lock() {}
  
  inline void lock() {}
  inline void unlock() {}
  inline void unlock_and_clear() { _lock = 0; }
  inline void unlock_and_set(T* val) { _lock = val; }
  inline T* getValue() const { return _lock; }
  inline void setValue(T* val) { _lock = val; }
  inline bool try_lock() const { return true; }
  inline bool is_locked() const { return false; }
  inline bool CAS(T* oldval, T* newval) {
    if (_lock == oldval) {
      _lock = newval;
      return true;
    }
    return false;
  }
  inline bool stealing_CAS(T* oldval, T* newval) {
    return CAS(oldval, newval);
  }
};

}
}
} // end namespace Galois

#endif

---