C# How to kill a blocked thread?

Question

I have a thread:

void threadCode(object o)
{
  doStuffHere(o); // Blocking call. Sometimes hangs.
}

and I'm calling it like this:

Thread t = new Thread(new ThreadStart(delegate()
  {
    threadCode(o);
  }));
t.Start();

StopWatch sw = new StopWatch();
sw.Start();

while (t.IsAlive)
{
  Application.DoEvents();

  if (sw.EllapsedMilliseconds > myTimeout)
    // Somehow kill t even though doStuffHere(o) is blocked (but hung)
}

I'm using the .NET Zip Library and calling ZipFile.CommitUpdate() which works most of the time, but sometimes just hangs. I don't know why, I can't see anything in the documentation which specifies why this is happening. A small file which should take no longer than 5 - 10 seconds will sometimes sit there for more then 5 minutes with no progress. I/O graphs in process explorer show that the process is not reading or writing, and there is no CPU usage. Basically, if this happens, I want to kill CommitUpdate() and try again once or twice before giving up.

Any idea how I can kill a thread stuck in a blocking call?

(Alternatively - those of you with experience with this zip library: do you know why it might be hanging with some files sometimes? I'm modifying the contents of .docx and .pptx (GZip) files. This would be an ideal solution.)

Answer 1

If you're going to terminate the hanging thread by using Thread.Abort(), make sure you handle ThreadAbortException in your thread code. The normal pattern is:

try {
    // do work here
}
catch (ThreadAbortException) {
    // allows your thread to gracefully terminate
    Thread.ResetAbort();
}
catch {
    // regular exception handling
}

If you don't follow the above pattern, then at best your threads will terminate ungracefully. At worst, you could run into a number of other problems.