Read-only access without blocking via access vectors

Abstract

A system and method for maintaining linked data structures stored in a computer system capable of processing the stored data as addressable object nodes, such that any data object node may be modified prior to the completion of outstanding read only accesses to that node. The system and method maintain an access vector for each node. The access vectors include an access counter which counts the number of read only accesses from a present node to the next node, and a link pointing to a next node. The number of read only accesses in effect for a node is the sum of access counts of all access vectors pointing to that node, minus the ADJ and minus the sum of access counts of all access vectors with access to that node. A node in the list can be replaced or deleted by first changing the pointers of all nodes that point to the node to point to a new one. Then, modifying the access count of the node by subtracting the maximum value of the access counts pointing to the node from the count in the node. Read only accesses out of the node continue to increment the access count, and when it reaches zero the node can be deleted. Because the pointers to the node had been changed, read only processes can continue without pausing for the change or replacement event.