C# Lock syntax - 2 questions

Question

Can I use string as locker in the Lock ?

lock(\"something\")

Can I do lock without braces if its only one line ?

lock(\"som         


        

Answer 1

Yes, you could use a string instance as the target of a lock. However, there are some really weird edge cases to consider.

Case 1: Literal vs. StringBuilder

In the following example the two locks will not use the same string instance. This is because the literal is interned, but the built instance is not.

string a = "something";
string b = new StringBuilder().Append("some").Append("thing").ToString();

// These are different.
lock (a)
lock (b)

However, we could manually intern the strings.

// These are the same.
lock (a)
lock (String.Intern(b))

Case 2: Version considerations

There are some differences with the way empty strings are interned from version to version.

string a = String.Empty;
string b = new StringBuilder().Append(String.Empty);

// These are the same in 1.0, 1.1, 3.5, and 4.0.
// These are different in 2.0 and 3.0.
lock (a);
lock (String.Intern(b))

Case 3: Implementation differences

Microsoft's implementation of the CLI is not the only one out there. It is conceivable that different implementations exhibit different behaviors and have their own set of caveats.

Case 4: CompilationRelaxations.NoStringInterning

Depending on whether assemblies are decorated with this and whether the CLR actually uses it (as opposed to ignoring it) may change the behavior of the interning mechanisms. This a particularly pernicious problem because it could mean that the same code behaves differently depending upon the context in which it was run.

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I am sure there are other edge cases that I am unaware of. However, the point is that relying on string instances for locking purposes (or any purpose that requires implicit assumptions about the equivalence of their references) is dangerous.