ooRexx allows for executing different parts of ooRexx programs on multiple threads of execution, even using different Rexx interpreter instances, within a single operating system process. This makes it difficult and at times even impossible to debug such multithreaded programs without any additional information about the specific execution context. Relevant information for debugging multithreaded programs may be: the Rexx interpreter instance that executes an invocation ("activation"), the operating system thread on which the activation is running, and whether a scope lock is held for exclusive access of an object's attribute ("object variable") pool at that specific scope.