METHOD AND SYSTEM FOR CONTROLLING MUTUALLY EXCLUSIVE RESOURCES USING A MODIFIED PETRI NET PROCESS CONTROL GRAPH

A method and system for controlling mutually exclusive resources and for preventing deadlocks in a multi-tasking computer system by generating a graph containing nodes to which are mapped the tasks included in a flow of processes and the critical resources which may be appropriated by at least one of the tasks. The nodes of tasks executed sequentially are arranged sequentially; the nodes of tasks executed in parallel are arranged in parallel with each other and each node of a critical resource is arranged in parallel with every node which may appropriate it. Every time a signal to being execution of a task is transmitted, a token is generated in the task node and the critical resource node is parallel with the task node. Referring to the graph, when the completion of the current task in the process flow is detected, a signal to being execution of the immediately succeeding task is delayed until a token is assigned to any one of the immediately succeeding task nodes and the critical resource nodes arranged in parallel with it.