Transfer of control method and means among hierarchical cooperating

Abstract

A method for transferring control between hierarchically related cooperating sequential processes P and Q executable in a multi-processing CPU environment. The method uses pointers to identify active and suspended processes. The method steps comprise generating and memory storing activation records; transferring control from process P to process Q, and updating the process pointers to record the suspension of process P and the activation of process Q; and resuming execution in the most recently executing subprocesses of Q by reference to the process pointers. There is stored in memory one activation record per process. The record includes a pointer to the activation that is the parent of the process, a pointer to the most recently executing subprocess of the process, and information defining the current execution state of the process. These pointers are further constrained such that the set of activation records form the nodes of a tree whose arcs are defined by the parent pointers. The descendants of any node P, together with P itself, constitute the subprocesses of P. For any node P the process pointer of P always points to a subprocess of P. The transfer of control from process P to process Q involves the concurrent updating of the process pointers to record the suspension of process P and the activation of process Q.