When is it appropriate to use either the Monitor
class or the lock
keyword for thread safety in C#?
EDIT:
It seems from the answers so far that lock
is short hand for a series of calls to the Monitor
class. What exactly is the lock call short-hand for? Or more explicitly,
class LockVsMonitor
{
private readonly object LockObject = new object();
public void DoThreadSafeSomethingWithLock(Action action)
{
lock (LockObject)
{
action.Invoke();
}
}
public void DoThreadSafeSomethingWithMonitor(Action action)
{
// What goes here ?
}
}
Update
Thank you all for your help : I have posted a another question as a follow up to some of the information you all provided. Since you seem to be well versed in this area, I have posted the link: What is wrong with this solution to locking and managing locked exceptions?
Eric Lippert talks about this in his blog: Locks and exceptions do not mix
The equivalent code differs between C# 4.0 and earlier versions.
In C# 4.0 it is:
bool lockWasTaken = false;
var temp = obj;
try
{
Monitor.Enter(temp, ref lockWasTaken);
{ body }
}
finally
{
if (lockWasTaken) Monitor.Exit(temp);
}
It relies on Monitor.Enter
atomically setting the flag when the lock is taken.
And earlier it was:
var temp = obj;
Monitor.Enter(temp);
try
{
body
}
finally
{
Monitor.Exit(temp);
}
This relies on no exception being thrown between Monitor.Enter
and the try
. I think in debug code this condition was violated because the compiler inserted a NOP between them and thus made thread abortion between those possible.