我无法捕捉异常

Question

I have this piece of code:

try
{
    var files = from folder in paths
                from file in Directory.EnumerateFiles(path, pattern, searchOption)
                select new Foo() { folder = folder, fileName = file };

    Parallel.ForEach(files, new ParallelOptions { MaxDegreeOfParallelism = _maxDegreeOfParallelism }, currentFile =>
    {
        DoWork(currentFile);
    });
}
catch (Exception ex)
{

}

When I have an exception in Directory.EnumerateFiles , I can't catch this exception in this piece of code. The exception is caught by the method that calls this snippet.

From Visual Studio, in debug mode, the exception is caught by Visual Studio (for example a DirectoryNotFoundException ).

Answer 1

The problem is that you are invoking the code asynchronously here:

Parallel.ForEach(files, new ParallelOptions { MaxDegreeOfParallelism = _maxDegreeOfParallelism }, currentFile =>
{
    DoWork(currentFile);
});

This makes the calls on separate threads and not on your main thread.

Use a try & catch block like this:

Parallel.ForEach(files, new ParallelOptions { MaxDegreeOfParallelism = _maxDegreeOfParallelism }, currentFile =>
{
    try
    { 
         DoWork(currentFile);
    }
    catch (Exception ex) { ... } 
});

Answer 2

If you want to catch the Directory not found exception you may add the two lines

catch (DirectoryNotFoundException dnfe)
{
  throw dnfe;
}

Answer 3

The best way to catch any exceptions that may be thrown while in the loop is to use System.AggregateException . This is because any exception thrown in any one thread in the loop might cause other threads to throw exceptions too.