C# 4 and .NET 4

synchronization ❘ 527
The Main() method of the program defines arrays of four ManualResetEventSlim objects and four
Calculator objects. Every Calculator is initialized in the constructor with a ManualResetEventSlim
object, so that every task gets its own event object to signal when it is completed. Now the TaskFactory
class is used to have different tasks running the calculation.
class Program
{
static void Main()
{
const int taskCount = 4;
var mEvents = new ManualResetEventSlim[taskCount];
var waitHandles = new WaitHandle[taskCount];
var calcs = new Calculator[taskCount];
TaskFactory taskFactory = new TaskFactory();
for (int i = 0; i < taskCount; i++)
{
mEvents[i] = new ManualResetEventSlim(false);
waitHandles[i] = mEvents[i].WaitHandle;
calcs[i] = new Calculator(mEvents[i]);
taskFactory.StartNew(calcs[i].Calculation, Tuple.Create(i + 1, i + 3));
}
//...
The WaitHandle class is now used to wait for any one of the events in the array. WaitAny() waits until any
one of the events is signaled. In contrast to ManualResetEvent, ManualResetEventSlim does not derive
from WaitHandle. That’s why a separate collection of WaitHandle objects is kept that is filled from the
WaitHandle property of the ManualResetEventSlim class. WaitAny() returns an index value that provides
information about the event that was signaled. The returned value matches the index of the event array that
is passed to WaitAny(). Using this index the information from the signaled event can be read:
}
}
for (int i = 0; i < taskCount; i++)
{
int index = WaitHandle.WaitAny(mEvents);
if (index == WaitHandle.WaitTimeout)
{
Console.WriteLine("Timeout!!");
}
else
{
mEvents[index].Reset();
Console.WriteLine("finished task for {0}, result: {1}",
index, calcs[index].Result);
}
}
code snippet EventSample/Program.cs
When starting the application, you can see the threads doing the calculation and setting the event to inform
the main thread that it can read the result. At random times, depending on whether the build is a debug
or release build and on your hardware, you might see different orders and also a different number of threads
from the pool performing tasks. Here, thread 4 was reused from the pool for doing two tasks because it was
fast enough to finish the calculation first:
Task 1 starts calculation
Task 2 starts calculation
Task 2 is ready
Task 3 starts calculation
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