When you "lock" an object, there's no protection against other threads
accessing that object. The system simply enforces the constraint that
only 1 thread that "asks" for the lock will be granted that lock at a
time. You need to ensure that every place in your code that accesses
your array list asks for the same lock first. The object referenced
in your lock statement doesn't even have to be the object you're
trying to protect. As long as every place in the code that accesses
the array list uses the same lock, you're fine.
class myclass
{
private ArrayList myList = new ArrayList();
void func1()
{
// will block if any other thread holds a lock on myList
lock(myList)
{
foreach(Item myItem in myList)
...
}
}
void func2()
{
// not protected. Even if another thread holds a lock, access is not
// prevented here.
myList.Add(anotherItem);
}
}
To fix this sample, you'd wrap the myList.Add() statement with
lock(myList). The synchronization system here provides protection
against concurrency only when everybody plays by the same rules.
--
Steve Johnson
On Tue, 12 Oct 2004 21:07:46 +1300, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> I am having trouble understanding .net and c#'s lock command
>
> What happens if a lock is called on a object that is already being used
> by another process.
>
> I am getting weird behavior in dotnet remoting to do with threads.
>
> If i put a lock on all methods in there, i get a deadlock which i would
> expect, but when i only put a lock on the only method that enumerates
> through a arraylist i get a enumeration violation because of
> modification to the array during enumeration. I dont see how this is
> possible if i put a lock on the object that contains the arraylist while
> i enumerate through it. ?!?!?!?!
>
> I am thinking if another thread already is already in that object both
> may execute at the same time regardsless of the lock block.
>
> Can anyone confirm or deny my theory and give me some advice on what
> might be going on.
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