nsdictionary objectforkey - search and get that value

Question

I'm using NSDictionary in my iphone app. I am using "objectForKey:" method to get the value of a key. One thread (first thread) is adding key-value to a dictionary and other thread (second thread) is reading them. In second thread, i want to get a value for a key which first thread some times didn't add by that time. So, in 2nd thread i want search for some key and then get that value. Possible? What if I provide a key in dictionary that doesn't exist? what will it return?

Answer 1

You need to use NSLock to synchronize access to your dictionary, in order for your operation to be threadsafe. As for your question about the [NSDictionary -objectForKey] method, according to the documention, it will return nil if the key is not present (i.e. has no associated value) in the dictionary.