lock inside lock

Question

I\'m wondering if this construction will cause an error:

lock(sync)
{
  // something
  lock(sync)
  {
    //something
    lock(sync)
    {
      //something
             


        

Answer 1

To explain why it is well-defined behavior and will never fail:

Aside: This answer has better details about how locks actually work

The lock occurs at the Thread level, so calling it a second time on the same thread will be redundant. I would think it would not have any performance penalty (although that would depend on how exactly the internals of .Net are written, so I can't guarantee that)

Many times you'd have a public function that calls another public function in your class, whom both need the lock when used seperately. If this was not allowed the following would fail:

private Dictionary database = new Dictionary();
private object databaseLock = new object();
public void AddOrUpdate(string item)
{
    lock (databaseLock)
    {
        if (Exists(item))
            database.Add(item, 1);
        else
            ++database[item];
    }
}
public bool Exists(string item)
{
    lock (databaseLock)
    {
        //... Maybe some pre-processing of the key or item...
        return database.ContainsKey(item);
    }
}