A program debugging system for a distributed data processing system of the type in which a plurality of processes communicate with one another to realize their concurrent and parallel operations. The debugging system includes a plurality of satellite debugging units, coupled respectively with the plurality of processes, for debugging the processes; a central debugging unit for remotely controlling the plurality of satellite debugging units; and a remote-procedure-call detecting unit for previously detecting an issuance or an end of a remote procedure call in the process to be debugged by the satellite debugging units. In the debugging system, each of the satellite debugging units includes an execution interrupting unit for interrupting the execution of the process to be debugged and transmitting a message of the execution-interruption to the central debugging unit; an execution restarting unit for restarting the execution of the interrupted process and transmitting a message of the execution-restart to the central debugging unit; an interruption-time notifying unit for calculating an execution-interruption time on the basis of the interruption and restart of the execution of the process and for transmitting the calculated interruption time to the central debugging unit; and an execution delay unit for delaying, when the remote-procedure-call detecting unit detects the issuance of a remote procedure call by a process, the execution of the remote procedure call according to information including the execution-interruption time of another process that is transmitted from the central debugging unit.

An apparatus and method for implementation in a computing system (5) which allows the transfer of control from one process (10) to another process (40). The input/output supervisor (20) and a newly provided control mechanism (50) are used to switch control. Transfer of data between the two processes is carried out using a data pool (75). This data pool (75) is accessible to both processes (10, 40) through the control mechanism (50).

A data processing system (1) comprising distributed data storage resource (D.sub.1 -D.sub.3, FD.sub.6, TL.sub.4, STO.sub.e) under the control of a distributed management unit (DSM.sub.1 through DSM.sub.6), which may or may not be associated with a server (S.sub.1 through S.sub.3) . This unit receives, from a centralized management unit (NSM), control programs which dynamically allocate to the unit to a virtual memory space comprising local storage units and all or some of the external storage resources.

A tiered communications service which utilizes multiple methods of communication and provides the ability for different host computer systems to pass dam, unconcerned with the type of communications medium used by the service. Each method of communication is ranked according to its preference within the service. When the communications service encounters an error while attempting to send data to another host system, it performs an automatic switch to the method with the next lower preference which is available for use. The service sends notification to the other system of the change in communications method used and which method to start using, then continues sending the data. The communications method may be switched to a higher or lower preferred method explicitly by operator command, which also sends notification to the other systems of a change in method. Each host system has the ability to communicate with other host systems via various communications methods, depending on the methods defined to the service. A host system can communicate with a second host system using one communications method and communicate with a third host computer system using a different communications method. To communicate between any two host systems, the service utilizes the highest preferred common communications method available for use, except when changed by operator command.

An event management service (EMS) operating in a distributed computing environment includes a queueing mechanism for controlling passage of events through an event channel when multiple event consumers cannot consume events being generated by one or more event suppliers as the events are being generated. The queueing mechanism includes a number of queues: an input queue that receives queue elements for each event that reaches the service, an active queue that receives queue elements for each event that any event consumer has registered to receive, and a consumer queue for each event consumer registered to receive any event. A multi-threaded process control routine processes the queue elements to control passage of the events to the event consumers.