Recording the thread ID in Mac OS X Instruments

Hidden in the depths of the man page for dtrace(1), there is a reference to a new built-in variable, tid:

tid A uint64_t thread ID of the currently executing thread…

What this means is that it’s trivial to log the thread ID associated with a call, which is incredibly useful for multi-threaded applications. (Can you say, “GCD?” I knew you could.) In a custom probe, you can record it as follows: