Hello!
I am working on improving my threading skills and came across a question.
When working with the ReaderWriterLock class, I am getting an unhandled
exception if I acquire a WriterLock with a timeout less than the time
required to process the code section it protects.
The code listed below is just a small application I wrote to check the
behavious of the different threading / synchronization techniques. Basically
the application spins 10 threads with target method that acquires a
WriterLock (timout: 1000 ms) and simulates a long running operation (thread
sleeps for 500 ms).
A third thread that acquired the WriterLock times out, because the previous
two threads spent the available time with a long running process.
The logic answer I can think of is, that if one specifies a timeout, then
the CLR respects that and throws an exception regardless of what's inside
the code section. Handling the thrown exception is a matter of wrapping the
code section (including the acquisition of the WriterLock) in another
try/finally statement .. but that doesn't sound right.
A potential answer is to make sure that the timeout is sufficient for the
operations to complete (e.g. specify an infinite timeout).
...
Here's the error message from the unhandled exception:
An unhandled exception of type 'System.ApplicationException' occurred in
<application>. Additional information: This operation returned because the
timeout period expired.
Please look for "exception is thrown here" in the last method, to see where
I'm getting the exception.
class ThreadDriver
{
static ReaderWriterLock rwl = new ReaderWriterLock();
static void Main(string[] args)
{
Console.WriteLine("Spinning threads ..");
Thread[] threads = new Thread[10];
for (int i = 0; i < 10; i++)
{
Console.WriteLine("Spinning thread #{0}", i);
threads[i] = new Thread(new ThreadStart(Process));
threads[i].Name = "Thread ID: " + i;
threads[i].Start();
}
// Initiate join of spinning threads
for (int i = 0; i < 10; i++) { threads[i].Join(); }
// Calling thread is put on hold ..
Console.WriteLine("Press any key to continue ..");
Console.Read();
}
static void Process()
{
// Acquire lock with a short timeout
rwl.AcquireWriterLock(1000);
try
{
// Identify thread - exception is thrown here
Console.WriteLine(Thread.CurrentThread.Name);
// Simulates a long running process
Thread.Sleep(500);
}
catch (ApplicationException e)
{
Console.WriteLine(Thread.CurrentThread.Name + " failed " +
e.Message);
}
finally { rwl.ReleaseWriterLock(); }
}
I tried googling around looking for a direct answer but couldn't find one.
Not even the threading book from Wrox gives an answer to this (or I haven't
seen it :-).
Thanks in advance.
--
venlig hilsen / with regards
anders borum
--
