A Performance Comparison of ReaderWriterLockSlim with ReaderWriterLock

If you have ever used the System.Threading.ReaderWriterLock to achieve synchronised access to shared resources which are frequently read but infrequently updated then you probably know why we have created a new Reader/Write lock. In this MSDN Magazine’s concurrent affairs column, Jeffery Richter explains some of the short comings of the existing ReaderWriterLock in .NET Framework.

One of the hidden gems of the new .NET Framework 3.5 is a fast Reader/Writer lock called “ReaderWriterLockSlim”. If you are not familiar with this new lock then read this blog entry.

Before recommending this new lock to my customers, I wanted to see some comparisons with Monitor and the existing ReaderWriterLock. So, I devised the following comparison tests:

- Acquiring a Read lock in comparison with taking a lock using Monitor

- Acquiring a Write lock in comparison with taking a lock using Monitor

- Acquiring a Read/Write lock in comparison with taking a Read/Write lock using ReaderWriterLock

Read lock comparison with Monitor

After executing the test for 1000 times, it became apparent that ReaderWriterLockSlim with no recursion support is 1.67 times slower than Monitor and it is 1.74 times slower when recursion is supported:

Write lock comparison with Monitor

ReaderWriterLockSlim, in average, is 1.71 times slower than Monitor, and when recursion is supported it is 1.77 times slower.

It also turns out that acquiring a Read lock using the new slim lock class is slightly quicker than taking a Write lock.

ReaderWriterLockSlim in comparison with ReaderWriterLock

ReaderWriterLock is significantly slower than its successor:

- Taking a ReaderWriterLockSlim Read lock is almost 3 times quicker than ReaderWriterLock

- Taking a ReaderWriterLockSlim Write lock is 2.8 times quicker than ReaderWriterLock

Results at a glance:

The table below compares both Reader/Writer locks with Monitor:

The above comparison was performed on a Toshiba M400 with a Centrino Duo processor using Visual Studio 2008 beta 2.

Comments

• Anonymous
  October 07, 2007
  PingBack from http://www.artofbam.com/wordpress/?p=5919

• Anonymous
  January 14, 2008
  The comment has been removed

• Anonymous
  January 14, 2008
  A reader-writer lock allows for multiple concurrent reads to enter a read-lock all at the same time and depending on the scenario, it can significantly improve the overall performance of your application when used instead of a mutual exclusive lock. A read-lock takes a shared lock and a write-lock takes an exclusive lock. The new ReaderWriterLockSlim correctly gives priority to write requests therefore only use when reads are frequent and writes are less common. Hope that clarifies it. Pedram

• Anonymous
  December 21, 2008
  Clearly the Monitor is the preferred mechanism if you only have a couple of simultaneous reader threads. You can have hundreds of threads, the question is how many of those are going to try concurrently read the writable resource? With an average of 10 concurrent accesses, you're going to have to wait an average of 10 times longer than "slim" users. I noticed the "slim" version collects some nice metrics. You may determine you're not bottlenecking, but ironically you might not care that "slim" takes 0.7 times longer and keep using it.

• Anonymous
  February 08, 2012
  very interesting, thank you. I think I will not use it! carole