Synchronization tracing is implemented by interposing on the various library functions for synchronization, such as mutex_lock(), pthread_mutex_lock(), sem_wait(), and so on. Both the pthread and Oracle Solaris synchronization calls are traced.
When the target program calls one of these functions, the call is intercepted by the data collector. The current time, the address of the lock, and some other data is captured, and then the interposition routine calls the real library routine. When the real library routine returns, the data collector reads the time again and computes the difference between the end-time and the start-time. If that difference exceeds a user-specified threshold, the event is recorded. If the time does not exceed the threshold, the event is not recorded. In either case, the return value from the real library routine is returned to the caller.
You can set the threshold used to determine whether to record the event by using the collect command's -s option. If you use Performance Analyzer to collect the experiment, you can specify the threshold as the Minimum Delay for Synchronization Wait Tracing in the Profile Application dialog. You can set the threshold to a number of microseconds or to the keyword calibrate or on. When you use calibrate or on the data collector determines the time it takes to acquire an uncontested mutex lock and sets the threshold to five times that value. A specified threshold of 0 or all causes all events to be recorded.
In this tutorial, you record synchronization wait tracing in two experiments, with one experiment having a calibrated threshold and one experiment with a zero threshold. Both experiments also include clock profiling.