International Business Machines Corporation

Richard T Turner

Roy L Hoffman

Frank G Soltis

William G Kempke

John W McCullough

Keith K Slack

Dale N Reynolds

Terrell A Poland

J Warren McCullough

A method and apparatus are provided to enable interruption of list processing operations in a computer system and to enable restart from the point of interruption. A mechanism, at a predetermined point of the list processing operation, operates to recognize occurrences of interrupting events. If any such events are present, a mechanism saves the status of the list processing operation, saves the identification of the task associated with instruction executing the list processing operation and locks the list or queue. After the interrupt is handled, a mechanism restores status, and unlocks the list or queue only when the identified task is active again and the instruction which had been executing the list processing operation is again executing.

Process and apparatus for interrupting and restarting sequential

Improved task handling apparatus for a computer system where the task dispatcher is selectively operable under instruction control for performing task queue selection and where the intertask communication mechanism can return a task dispatching element (TDE) to a non-prime task dispatching queue (TDQ) as well as to the prime TDQ. Whenever a TDE is returned to the prime TDQ, the task dispatcher makes a pre-emptive task switch. Also, if there are no task dispatching elements on the current non-prime TDQ, the task dispatcher switches to dispatch TDE's from the prime TDQ.

Task handling apparatus

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.

Synchronous and conditional inter-program control apparatus for a

Task handling apparatus in a computer system is structured to be common to system control tasks, user tasks and I/O tasks. Although the task handling apparatus contains a task priority structure, all tasks are handled in the same manner, and there are no fixed interrupt levels for I/O tasks. There are N levels of priority, and N is variable. Each task is a server for a functional request. Task dispatching elements (TDE's) are enqueued in priority sequence on a task dispatching queue (TDQ). A task dispatcher functions to dispatch the highest priority TDE on the TDQ, if any, and to perform task switching. Intertask communication is accomplished by send message, send count, receive message and receive count mechanisms, and is coupled with task synchronization. Task synchronization is achieved by dequeueing and enqueueing TDE's on the TDQ. An active task becomes inactive dispatchable when a higher priority TDE is enqueued on the TDQ by send message or send count mechanisms. The active task becomes inactive waiting when a receive message or receive count is not satisfied. An inactive dispatchable task becomes the active task when it becomes the highest priority enqueued TDE on the TDQ by the receive message or receive count mechanisms. An inactive waiting task becomes either the active task or an inactive dispatchable task after being enqueued on the TDQ by the send message or send count mechanisms, depending upon whether it is the highest or other than the highest priority TDE on the TDQ.

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Rochester, MN, United States of America

Richard T Turner