ACCESS CONTROL SYSTEM FOR SHARED RESOURCES

摘要

PURPOSE:To maintain a lock control area with no conflict through plural tasks by providing a lock control area and a task control table on a memory device which is referred to by those tasks and replacing these area and table with a single instruction. CONSTITUTION:When a lock request is received, the contents of a lock control area are loaded to a pair of registers Ra5 and Rb6 respectively and the presence or absence of the lock is checked. In case no lock is held with the Ra5 kept at '0', the information '1' showing a lock is set to a register Rc7 together with the contents of the Rb6 set to a register Rd8. Then the lock control area is replaced. It is checked whether the contents of the lock control area are coincident or not with the contents of the Ra5 and Rb6 read out previously. If the coincidence is obtained, the contents of the Rc7 and Rd8 are written to the lock control area just with a single instruction and complete the replacement processing to start an access to the resources. If no coincidence is obtained, the contents of both Ra5 and Rb6 are read out again to continue the following processing.