You have a hierarchy of objects:
- You have servers (10)
- On each server you have processes (probably only 1 - your service/app pool)
- In each process you have threads (probably many)
Your code will only prohibit threads within the same process on the same server access to modify the Cache
object simultaneously. You can create locks across processes and even across servers, but the cost increases a lot as you move up the hierarchy.
Using the lock
statement does not actually lock any threads. However, if one thread is executing code inside the lock (that is in the block of code following the lock
statement) any other thread that wants to take the lock and execute the same code has to wait until the first thread holding the lock leaves the block of code and releases the lock.
The C# lock
statement uses a Windows critical section which a lightweight locking mechanism. If you want to lock across processes you can use a mutex instead. To lock across servers you can use a database or a shared file.
As dkackman has pointed out .NET has the concept of an AppDomain that is a kind of lightweight process. You can have multiple AppDomains per process. The C# lock
statement only locks a resource within a single AppDomain, and a proper description of the hierarchy would include the AppDomain below the process and above the threads. However, quite often you only have a single AppDomain in a process making the distinction somewhat irrelevant.
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