Why is lock much slower than Monitor.TryEnter?

Question

Results

Lock: 85.3 microseconds

Monitor.TryEnter: 11.0 microseconds

Isn\'t the lock expanded into the same code?

Edit: Results with 1000 iteratio

Answer 1

100 is far too few, and running in a test framework may skew things. It is also possibly (see comments) related to any additional cost associated with the first lock against an object; try:

• locking once outside the loop first
• doing lots more iterations
• in a console exe, at the command line, in release mode

Also, note that in 4.0 lock is not Monitor.Enter(object) - so expect different results in 4.0.

But I get:

lock: 3548ms
Monitor.TryEnter: 7008ms
Monitor.TryEnter (2): 2947ms
Monitor.Enter: 2906ms

From the test rig:

using System;
using System.Diagnostics;
using System.Threading;
static class Program {
    static void Main()
    {
        const int lockIterations = 50000000;
        object object1 = new object();
        lock (object1) { Console.WriteLine("First one has to pay an extra toll"); }
        Stopwatch csLock = Stopwatch.StartNew();
        for (int i = 0; i < lockIterations; ) {
            lock (object1) { i++; }
        }
        csLock.Stop();
        Console.WriteLine("lock: " + csLock.ElapsedMilliseconds + "ms");

        Stopwatch csMonitorTryEnter = Stopwatch.StartNew();
        for (int i = 0; i < lockIterations; ) {
            if (Monitor.TryEnter(object1, TimeSpan.FromSeconds(10))) {
                try { i++; } finally { Monitor.Exit(object1); }
            }
        }
        csMonitorTryEnter.Stop();
        Console.WriteLine("Monitor.TryEnter: " + csMonitorTryEnter.ElapsedMilliseconds + "ms");

        csMonitorTryEnter = Stopwatch.StartNew();
        for (int i = 0; i < lockIterations; ) {
            if (Monitor.TryEnter(object1, 10000)) {
                try { i++; } finally { Monitor.Exit(object1); }
            }
        }
        csMonitorTryEnter.Stop();
        Console.WriteLine("Monitor.TryEnter (2): " + csMonitorTryEnter.ElapsedMilliseconds + "ms");

        Stopwatch csMonitorEnter = Stopwatch.StartNew();
        for (int i = 0; i < lockIterations; ) {
            Monitor.Enter(object1);
            try { i++; } finally { Monitor.Exit(object1); }
        }
        csMonitorEnter.Stop();
        Console.WriteLine("Monitor.Enter: " + csMonitorEnter.ElapsedMilliseconds + "ms");
    }
}