Hello,
I have a multithreaded application written in c#. What i noticed is that implementing thread synchronization with lock(this) method slows down the application by 20%. Is that an expected behavior or should i look into the implementation closer?
Depending on how coarse or granular your lock() statements are, you can indeed impact the performance of your MT app. Only lock things you really know are supposed to be locked.
Any synchronization will slow down multithreading.
That being said, lock(this) is really never a good idea. You should always lock on a private object used for nothing but synchronization when possible.
Make sure to keep your locking to a minimum, and only hold the lock for as short of a time as possible. This will help keep the "slowdown" to a minimum.
Locking does add some overhead, that can't be avoided. It is also very likely that some of your threads now will be waiting on resources to be released, rather than just grabbing them when they feel like. If you implemented thread synchronization correctly, then that is a good thing.
But in general, your question can't be answered without intimate knowledge about the application. 20 % slowdown might be OK, but you might be locking too broadly, and then the program would (in general) be slower.
Also, please dont use lock(this). If your instance is passed around and someone else locks on the reference, you will have a deadlock. Best practice is to lock on a private object that noone else can access.
There are performance counters you can monitor in Windows to see how much time your application spends contending for locks.