Issue writing to single file in Web service in .NET

Question

I have created a webservice in .net 2.0, C#. I need to log some information to a file whenever different methods are called by the web service clients.

The problem comes when one user process is writing to a file and another process tries to write to it. I get the following error:

The process cannot access the file because it is being used by another process.

The solutions that I have tried to implement in C# and failed are as below.

1. Implemented singleton class that contains code that writes to a file.
2. Used lock statement to wrap the code that writes to the file.
3. I have also tried to use open source logger log4net but it also is not a perfect solution.
4. I know about logging to system event logger, but I do not have that choice.

I want to know if there exists a perfect and complete solution to such a problem?

Answer 1

The locking is probably failing because your webservice is being run by more than one worker process. You could protect the access with a named mutex, which is shared across processes, unlike the locks you get by using lock(someobject) {...}:

Mutex lock = new Mutex("mymutex", false);

lock.WaitOne();

// access file

lock.ReleaseMutex();

Answer 2

You don't say how your web service is hosted, so I'll assume it's in IIS. I don't think the file should be accessed by multiple processes unless your service runs in multiple application pools. Nevertheless, I guess you could get this error when multiple threads in one process are trying to write.

I think I'd go for the solution you suggest yourself, Pradeep, build a single object that does all the writing to the log file. Inside that object I'd have a Queue into which all data to be logged gets written. I'd have a separate thread reading from this queue and writing to the log file. In a thread-pooled hosting environment like IIS, it doesn't seem too nice to create another thread, but it's only one... Bear in mind that the in-memory queue will not survive IIS resets; you might lose some entries that are "in-flight" when the IIS process goes down.

Other alternatives certainly include using a separate process (such as a Service) to write to the file, but that has extra deployment overhead and IPC costs. If that doesn't work for you, go with the singleton.