public void ShouldRunThreadsWithDistinctKeysInParallel()
{
// Arrange
var currentParallelism = 0;
var maxParallelism = 0;
var parallelismLock = new object();
// 100 threads, 100 keys
var threads = Enumerable.Range(0, 100)
.Select(i => new Thread(() => OccupyTheLockALittleBit(i)))
.ToList();
// Act
foreach (var thread in threads)
{
thread.Start();
}
foreach (var thread in threads)
{
thread.Join();
}
maxParallelism.Should().BeGreaterThan(10);
void OccupyTheLockALittleBit(int key)
{
using (KeyedSemaphore.Lock(key.ToString()))
{
var incrementedCurrentParallelism = Interlocked.Increment(ref currentParallelism);
lock (parallelismLock)
{
maxParallelism = Math.Max(incrementedCurrentParallelism, maxParallelism);
}
const int delay = 250;
Thread.Sleep(TimeSpan.FromMilliseconds(delay));
Interlocked.Decrement(ref currentParallelism);
}
}
}
public void ShouldRunThreadsWithSameKeysLinearly()
{
// Arrange
var runningThreadsIndex = new ConcurrentDictionary <int, int>();
var parallelismLock = new object();
var currentParallelism = 0;
var maxParallelism = 0;
// 100 threads, 10 keys
var threads = Enumerable.Range(0, 100)
.Select(i => new Thread(() => OccupyTheLockALittleBit(i % 10)))
.ToList();
// Act
foreach (var thread in threads)
{
thread.Start();
}
foreach (var thread in threads)
{
thread.Join();
}
// Assert
maxParallelism.Should().BeLessOrEqualTo(10);
void OccupyTheLockALittleBit(int key)
{
using (KeyedSemaphore.Lock(key.ToString()))
{
var incrementedCurrentParallelism = Interlocked.Increment(ref currentParallelism);
lock (parallelismLock)
{
maxParallelism = Math.Max(incrementedCurrentParallelism, maxParallelism);
}
var currentThreadId = Thread.CurrentThread.ManagedThreadId;
if (runningThreadsIndex.TryGetValue(key, out var otherThread))
{
throw new Exception($"Thread #{currentThreadId} acquired a lock using key ${key} " +
$"but another thread #{otherThread} is also still running using this key!");
}
runningThreadsIndex[key] = currentThreadId;
const int delay = 10;
Thread.Sleep(TimeSpan.FromMilliseconds(delay));
if (!runningThreadsIndex.TryRemove(key, out var value))
{
var ex = new Exception($"Thread #{currentThreadId} has finished " +
$"but when trying to cleanup the running threads index, the value is already gone");
throw ex;
}
if (value != currentThreadId)
{
var ex = new Exception($"Thread #{currentThreadId} has finished and has removed itself from the running threads index," +
$" but that index contained an incorrect value: #{value}!");
throw ex;
}
Interlocked.Decrement(ref currentParallelism);
}
}
}
