/// <summary>
/// Enters an upgradeable lock (it is a read lock, but it can be upgraded).
/// Only one upgradeable lock is allowed at a time.
/// </summary>
public void EnterUpgradeableLock()
{
//var spinWait = new SpinWait();
while (true)
{
LockIntegralType result = Interlocked.Add(ref _lockValue, _upgradeLockValue);
if ((result >> _upgradeBitShift) == 1)
{
return;
}
Interlocked.Add(ref _lockValue, _upgradeUnlockValue);
var spinCount = 0;
while (true)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, _upgradeLockValue, 0);
if (result == 0)
{
return;
}
if ((result >> _upgradeBitShift) == 0)
{
break;
}
}
}
}
/// <summary>
/// Enters a read lock.
/// </summary>
public void EnterReadLock()
{
//var spinWait = new SpinWait();
while (true)
{
LockIntegralType result = Interlocked.Increment(ref _lockValue);
if ((result >> _writeBitShift) == 0)
{
return;
}
Interlocked.Decrement(ref _lockValue);
var spinCount = 0;
while (true)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, 1, 0);
if (result == 0)
{
return;
}
if ((result >> _writeBitShift) == 0)
{
break;
}
}
}
}
/// <summary>
/// upgrades to write-lock. You must already own a Upgradeable lock and you must first exit the write lock then the Upgradeable lock.
/// </summary>
public void UncheckedUpgradeToWriteLock()
{
//var spinWait = new SpinWait();
LockIntegralType result = Interlocked.Add(ref _lockValue, _writeLockValue);
var spinCount = 0;
while ((result & _allReadsValue) != 0)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, 0, 0);
}
}
/// <summary>
/// Enters write-lock.
/// </summary>
public void EnterWriteLock()
{
LockIntegralType result = Interlocked.CompareExchange(ref _lockValue, _writeLockValue, 0);
if (result == 0)
{
return;
}
var spinCount = 0;
//var spinWait = new SpinWait();
// we need to try again.
for (int i = 0; i < 100; i++)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, _writeLockValue, 0);
if (result == 0)
{
return;
}
// try to be the first locker.
if ((result >> _writeBitShift) == 0)
{
break;
}
}
// From this moment, we have priority.
while (true)
{
result = Interlocked.Add(ref _lockValue, _writeLockValue);
if (result == _writeLockValue)
{
return;
}
if ((result >> _writeBitShift) == 1)
{
spinCount = 0;
// we obtained the write lock, but there may be readers,
// so we wait until they release the lock.
while (true)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, 0, 0);
if (result == _writeLockValue)
{
return;
}
}
}
else
{
// we need to try again.
Interlocked.Add(ref _lockValue, _writeUnlockValue);
spinCount = 0;
while (true)
{
//spinWait.SpinOnce();
Spin.Wait(spinCount++);
result = Interlocked.CompareExchange(ref _lockValue, _writeLockValue, 0);
if (result == 0)
{
return;
}
// try to be the first locker.
if ((result >> _writeBitShift) == 0)
{
break;
}
}
}
}
}
