Synchronous and conditional inter-program control apparatus for a

Abstract

Synchronous and conditional inter-program control apparatus in a computer system is structured to temporarily suspend execution of an invoking program and to transfer processor control to an invoked program. Such transfer is initiated by a transfer initiation means which interacts with a function control means of a function control array and provides symbolic identification of an entry point in the invoked program and conditionally continuing the transfer mechanism. The function control means addresses call return elements (CRE's) when it is in an execute mode but transfers processor control back to the invoking program when it is in a by-pass mode. CRE's that are in an available, data-receivable state are chained on an available call return queue (ACQ) and may be removed therefrom and placed on a task dispatching element (TDE) on an as-needed basis through a receive message mechanism. Active CRE's contain a status save means for storing the state of the invoking program during execution of the invoked program. In the event there are no active CRE's available for such storage, a task switch occurs, and the current TDE, i.e., the invoking program, is inserted on a wait list of the ACQ where it remains until a CRE becomes available. When the CRE becomes available, the invoking program TDE is removed from the ACQ wait list and inserted in priority sequence on the task dispatching queue (TDQ). Once a CRE is made available to the TDE, the transfer initiation means is restarted. At the termination of the execution of the invoked program, a transfer return means transfers processor control back to the invoking program and inserts the CRE onto the ACQ. The invoking program then commences execution at the next sequential instruction.