C# 锁定语句

Question

Im going to use the C# lock statement and im wondering if i call a function while inside a lock, and that function also does a lock on the same object will the program freeze?

For example:

Object object;

public void f0()
{
   f1(object);
}

public void f1(Object obj1)
{
   lock (obj1) {
       f2(obj1);
   }
}

public void f2(Object obj2)
{
  lock(obj2) {
      /// do operations using obj2
  }
 }

Here function f0 calls function f1 which does a lock, inside that lock it calls f2 which also does a lock. So will the program freeze in f2 waiting for the object locked in f1?

I have a big program with functions calling each other passing objects around, and i need to lock some objects, but it may happen that the function i call may also lock the same object, so it may get locked twice, causing possible deadlock.

It may be difficult to know if the same objects gets passed around and may end up getting locked twice.

Also my program has multi-threading and multiple classes.

Also what if one thread gets an exception inside the lock, will it somehow unwind and fix itself?

Anybody knows the proper way to do this? I have a big program so before i start changing everything i decide i better find out the proper way to do it.

Thanks

Answer 1

Monitor (which is used by the lock statement under the covers) is reentrant, so it's technically ok for the same thread to lock on an object multiple times. The lock will be released when the outer lock scope completes. However, reentrant locks are difficult to reason about and should be avoided unless you have no other option.

Deadlocks do not occur due to reentrant locks. They occur when you take out locks on multiple objects while some other thread locks the same objects in a different order.

Answer 2

锁定对象使其成为简单的单线程代码，可用于防止混淆或过早计算（这只是一个示例）。