ASMX Web Service Method Singleton

Question

Not sure if this is the right terminology, let me explain what I want.

I have a web service that's available on the network - the web service has 1 web method.

What I want is... if the web service is running and performing tasks and another call is made to this web service, I want the 2nd call to fail or pend for a certain period of time then fail. Because only 1 instance of this web service should be called at once.

I was thinking of writing a value to the application object (like in asp.net) but then I have to be very careful to make sure that this value gets updated, in case of any errors, it might not... so this is dangerous, and would leave the web service in a state where no one can get to it.

Is there not a more dynamic way to determine if the web service is getting called or not?

Answer 1

If you are using WCF, this is simple. Use the service throttling settings to specify that you want MaxConcurrentCalls = 1 and MaxInstances = 1. You'll also want to set the ConcurrencyMode to Single for your ServiceBehavior .

Answer 2

You cannot do this with legacy ASMX web services. They have no support for different instance schemes.

I believe you can do this with WCF, as you can configure the service to have only a single instance.

Answer 3

I dont know much about web services on whether you can configure a web server to only start 1 instance of your web service, but you could try creating a mutex within your web service.

A Mutex is an interprocess synchronization object which can be used to detect if another instance of your web service is running.

So, what you can do is create a mutex with a name, then Wait on it. If more than 1 instance of your web service is alive, then the mutex will wait.

Answer 4

您可以在web方法内部实施检查，因为它将在同一IIS进程中运行

Answer 5

You could create a poor man's mutex and have the first instance create a file and have consecutive instances check the existence of the file. Try Catch your web method and place the deletion of the file in the finally.

Answer 6

If you are WCF I recommend "bobbymcr" answer, but for legacy web service you can use Monitor instead or mutex as mutex is costly (because it is a kernel object) but if you do not care about performance and responsiveness of the service use the Mutex simply.

See this sample for using Monitor class

private static object lockObject = new object();

public void SingleMethod()
{
try
{
Monitor.TryEnter(lockObject,millisecondsTimeout);
//method code
}
catch
{
}
finally
{
Monitor.Exit(lockObject);
}

}