Question

I have a situation where a block of code should be executed only if two locker objects are free.

I was hoping there would be something like:

lock(a,b)
{
    // this scope is in critical region
} 

However, there seems to be nothing like that. So does it mean the only way for doing this is:

lock(a)
{
    lock(b)
    {
        // this scope is in critical region
    }
}

Will this even work as expected? Although the code compiles, but I am not sure whether it would achieve what I am expecting it to.

Answer 1

I’d expect it to, though there’d be a case where it could potentially cause a deadlock condition.

Normally, the code will attempt to lock a and then proceed to lock b if that succeeded. This means that it would only execute the code if it could lock both a and b. Which is what you want.

However, if some other code has already got a lock on b then this code will not do what you expect. You’d also need to ensure that everywhere you needed to lock on both a and b you attempt to get the locks in the same order. If you get b first and then a you would cause a deadlock.