/// <summary>
/// Locks the monitor, with the specified timeout. This implementation validates
/// the ordering of locks, and maintains the current owner.
/// </summary>
/// <param name="timeout">The timeout, in milliseconds. Must be Timeout.Infinite,
/// or non-negative.</param>
/// <returns>A lock token which should be disposed to release the lock</returns>
/// <exception cref="LockTimeoutException">The operation times out.</exception>
/// <exception cref="LockOrderException">
/// The lock order would be violated if this lock were taken out. (i.e. attempting
/// to acquire the lock could cause deadlock.)
/// </exception>
public override LockToken Lock(int timeout)
{
// Check whether we should be allowed to take out this lock, according to
// the inner locks we have.
// Performance note: This would be in a separate method, but the cost of
// making a method call (which can't be inlined in this case) is sufficiently
// high as to make it worth manually inlining.
OrderedLock inner = InnerLock;
// Performance note: This would be a single if statement with shortcutting,
// but fetching the current thread is mildly expensive.
if (inner != null)
{
Thread currentThread = Thread.CurrentThread;
if (Owner != currentThread)
{
while (inner != null)
{
if (inner.Owner == currentThread)
{
throw new LockOrderException("Unable to acquire lock {0} as lock {1} is already held",
Name, inner.Name);
}
inner = inner.InnerLock;
}
}
}
LockToken ret = base.Lock(timeout);
// Now remember that we've locked, and set the owner if necessary
// Performance note: On a single processor, it is slightly cheaper
// to assign owner every time, without a test. On multiple processor
// boxes, it is cheaper to avoid the volatile write.
if (Interlocked.Increment(ref count) == 1)
{
owner = Thread.CurrentThread;
}
return(ret);
}