public ObjectLockKey IssueSingleUseKey(Transaction transaction, LockIntention lockIntention)
{
try
{
lock (CriticalSections.AcquireLock)
{
var key = new ObjectLockKey(core, this, transaction.ProcessId, lockIntention.Operation);
Keys.Add(key);
return(key);
}
}
catch (Exception ex)
{
core.Log.Write("Failed to issue single use lock key.", ex);
throw;
}
}
public ObjectLock(Core core, LockIntention intention)
{
this.core = core;
this.DiskPath = intention.DiskPath;
this.LockType = intention.Type;
}
public bool IsObjectEqual(LockIntention intention)
{
return(intention.Type == this.Type &&
intention.DiskPath == this.DiskPath);
}
public bool IsEqual(LockIntention intention)
{
return(intention.Type == this.Type &&
intention.Operation == this.Operation &&
intention.DiskPath == this.DiskPath);
}
public void Acquire(Transaction transaction, LockIntention intention)
{
try
{
//We keep track of all transactions that are waiting on locks for a few reasons:
// (1) When we suspect a deadlock we know what all transactions are potentially involved
// (2) We are safe to poke around those transaction's properties because we know their threda are in this method.
lock (lockWaits)
{
lockWaits.Add(transaction, intention);
}
DateTime startTime = DateTime.UtcNow;
while (true)
{
lock (CriticalSections.AcquireLock)
{
if (transaction.IsDeadlocked)
{
core.Health.Increment(HealthCounterType.DeadlockCount);
throw new DokdexDeadlockException(String.Format("Deadlock occurred, transaction for process {0} is being terminated.", transaction.ProcessId));
}
//Find any existing locks:
List <ObjectLock> lockedObjects = new List <ObjectLock>();
if (intention.Type == LockType.File)
{
lockedObjects.AddRange((from o in objectLocks where o.LockType == LockType.File && o.DiskPath == intention.DiskPath select o).ToList());
}
else
{
lockedObjects.AddRange((from o in objectLocks where o.DiskPath.StartsWith(intention.DiskPath) select o).ToList());
}
lockedObjects.AddRange((from o in objectLocks where o.LockType == LockType.Directory && intention.DiskPath.StartsWith(o.DiskPath) select o).ToList());
if (lockedObjects.Count() == 0)
{
//No locks on the object exist - so add one to the local and class collections.
var lockedObject = new ObjectLock(core, intention);
this.objectLocks.Add(lockedObject);
lockedObjects.Add(lockedObject);
}
//We just want read access.
if (intention.Operation == LockOperation.Read)
{
var blockers = lockedObjects.SelectMany(o => o.Keys).Where(o => o.LockOperation == LockOperation.Write && o.ProcessId != transaction.ProcessId).ToList();
//If there are no existing un-owned write locks.
if (blockers.Count() == 0)
{
transaction.BlockedBy.Clear();
foreach (var lockedObject in lockedObjects)
{
var lockKey = lockedObject.IssueSingleUseKey(transaction, intention);
transaction.HeldLockKeys.Add(lockKey);
}
var lockWaitTime = (DateTime.UtcNow - startTime).TotalMilliseconds;
core.Health.Increment(HealthCounterType.LockWaitMs, lockWaitTime);
core.Health.Increment(HealthCounterType.LockWaitMs, intention.ObjectName, lockWaitTime);
return;
}
else
{
transaction.BlockedBy.Clear();
transaction.BlockedBy.AddRange(blockers.Select(o => o.ProcessId).Distinct());
}
}
//We want write access.
else if (intention.Operation == LockOperation.Write)
{
var blockers = lockedObjects.SelectMany(o => o.Keys).Where(o => o.ProcessId != transaction.ProcessId).ToList();
//If there are no existing un-owned locks.
if (blockers.Count() == 0)
{
transaction.BlockedBy.Clear();
foreach (var lockedObject in lockedObjects)
{
var lockKey = lockedObject.IssueSingleUseKey(transaction, intention);
transaction.HeldLockKeys.Add(lockKey);
}
var lockWaitTime = (DateTime.UtcNow - startTime).TotalMilliseconds;
core.Health.Increment(HealthCounterType.LockWaitMs, lockWaitTime);
core.Health.Increment(HealthCounterType.LockWaitMs, intention.ObjectName, lockWaitTime);
return;
}
else
{
transaction.BlockedBy.Clear();
transaction.BlockedBy.AddRange(blockers.Select(o => o.ProcessId).Distinct());
}
}
}
//Deadlock Search.
lock (lockWaits)
{
var actualWaiters = lockWaits.Keys.Where(o => o.IsDeadlocked == false).ToList();
if (actualWaiters.Count() > 1)
{
foreach (var waiter in actualWaiters)
{
var blockedByMe = (from o in actualWaiters where o != waiter && o.BlockedBy.Contains(waiter.ProcessId) select o).ToList();
if (blockedByMe != null && blockedByMe.Count > 0)
{
var blockingMe = (from o in blockedByMe where waiter.BlockedBy.Contains(o.ProcessId) select o).ToList();
if (blockingMe != null && blockingMe.Count > 0)
{
transaction.IsDeadlocked = true;
break;
}
}
}
}
}
System.Threading.Thread.Sleep(1);
}
}
catch (Exception ex)
{
core.Log.Write(String.Format("Failed to acquire lock for process {0}.", transaction.ProcessId), ex);
throw;
}
finally
{
lock (lockWaits)
{
lockWaits.Remove(transaction);
}
}
}
