Question

I have some records, that I want to save to database asynchronously. I organize them into batches, then send them. As time passes, the batches are processed.

In the meanwhile the user can work on. There are some critical operations, that I want to lock him out from, while any save batch is still running asynchronously.

The save is done using a TableServiceContext and method .BeginSave() – but I think this should be irrelevant.

What I want to do is whenever an async save is started, increase a lock count, and when it completes, decrease the lock count so that it will be zero as soon as all have finished. I want to lock out the critical operation as long as the count is not zero. Furthermore I want to qualify the lock – by business object – for example.

I did not find a .NET 3.5 c# locking method, that does fulfil this requirement. A semaphore does not contain a method to check, if the count is 0. Otherwise a semaphore with unlimited max count would do.

Answer 1

Actually the Semaphare does have a method for checking to see if the count is zero. Use the WaitOne method with a zero timeout. It will return a value indicating whether the semaphore was acquired. If it returns false then it was not acquired which implies that it’s count is zero.

var s = new Semaphore(5, 5);

while (s.WaitOne(0))
{
  Console.WriteLine("acquired");  
}

Console.WriteLine("no more left to acquire");