There may be unexpectedly high delays in ReaderWriterLockSlim operations #69206
Description
When the spin-lock used by ReaderWriterLockSlim internally is contended, the spin-lock falls back to Thread.Sleep(1) after some spin-waiting. The Sleep(1)s can delay the operation for some or many milliseconds depending on how much contention there is.
Repro:
using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
static class Program
{
private static void Main(string[] args)
{
var rwLock = new ReaderWriterLockSlim();
Action enterExit = () =>
{
var sw = Stopwatch.StartNew();
rwLock.EnterReadLock();
rwLock.ExitReadLock();
double elapsedMs = sw.Elapsed.TotalMilliseconds;
if (elapsedMs >= 0.5)
{
Console.WriteLine($"{elapsedMs,6:0.0} ms");
}
};
var tasks = new Task[100];
while (true)
{
for (int i = 0; i < 100; ++i)
{
tasks[i] = Task.Run(enterExit);
}
Task.WaitAll(tasks);
}
}
}Sample output:
0.9 ms
1.0 ms
0.8 ms
0.7 ms
1.0 ms
15.0 ms
15.0 ms
15.1 ms
15.1 ms
15.1 ms
15.1 ms
15.1 ms
30.6 ms
30.6 ms
30.6 ms
46.4 ms
14.3 ms
0.5 ms
0.5 ms