File IO within an ASP.NET MVC Action

Is it possible to use some kind of 'critical section' so that it is safe to do something like the following within an action...

public ActionResult GenerateTasks()
{
    string someDir = ....

    if (!Directory.Exists(someDir))
    {
        Directory.CreateDirectory(someDir);
    }

    ..开发者_开发百科.
}

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You can do this only by using a system-wide mutex. Process or app-domain locking primitives will fail to work under certain conditions (for instance when an application pool is recycled).

However, for the specific case here that's not necessary: Directory.CreateDirectory already does implement an existence check on its own, so that you shouldn't need to do anything in this regard.

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I'm assuming by your question that the concurrent safety you're interested in is whether or not the directory is created between the Directory.Exists and the Directory.CreateDirectory on a different thread. (If you're concerned about Directory.CreateDirectory throwing an exception if the directory already exists, it won't.) If so, and this is the point in your code that will have the potential to do that, then you can simply use a lock object to make these set of operations safe across multiple threads:

private static object lockObject = new object();

public ActionResult GenerateTasks()
{
    string someDir = ....

    lock(lockObject)
    {
        if (!Directory.Exists(someDir))
        {
            Directory.CreateDirectory(someDir);
        }
    }
    ...
}

This does not however make any garauntees that the directory isn't being interacted with outside of your control, say, in another application process.