Locking in .NET

• lock statement blocks execution of a code block for single thread that hold lock
• the same thread can acquire and release lock again
• any other thread is blocked from the statement
• lock on dedicated instance only
• using the same instance on multiple lock statements may lead to deadlock
• avoid using as lock
  • this, as it might be used by the callers as a lock
  • Type instances, as those might be obtained by the typeof operator or reflection
  • string instances, including string literals, as those might be interned
• Hold a lock for as short time as possible to reduce lock contention.

Below code block is translated by compiler

lock (x)
{
    // Your code...
}

to:

object __lockObj = x;
bool __lockWasTaken = false;
try
{
    System.Threading.Monitor.Enter(__lockObj, ref __lockWasTaken);
    // Your code...
}
finally
{
    if (__lockWasTaken) System.Threading.Monitor.Exit(__lockObj);
}

Further read:

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/statements/lock