Abstract: A method of controlling the execution of the threads of a first application such as a user application from a second application such as a debugger application running in a different address space. After initializing trace mode for the user application, the debugger waits for an event to occur on one of the threads of the user application. Upon the occurrence of an event on one of the user application threads, an event handler obtains control of the thread execution. The event handler suspends execution of the remaining threads in the application, posts the debugger and then suspends its own execution. When the debugger application has completed its debugging operations, it posts the event handler, which resumes execution of the suspended threads and returns control to the thread on which the event occurred.