Synchronizing Execution with Barrier Points
You can synchronize execution of threads and processes either manually using a hold command, or automatically by setting an action point called a barrier point. These two tools can be used together for fine-grained execution control. For instance, if a process or thread is held at a barrier point you can manually release it and then run it without first waiting for all other processes or threads in the group to reach that barrier.
When a process or a thread is held, it ignores any command to resume executing. For example, assume that you place a hold on a process in a control group that contains three processes. If you select Group > Go, two of the three processes resume executing. The held process ignores the Go command.
 
RELATED TOPICS 
 
Setting barrier points
Using barrier points in a multi-threaded, multi-process program
Using the CLI to set barrier points
Strategies for using barrier points