Shared resource lockout apparatus.

摘要

A system having a plurality of units includes a shareable unit which is shareable between two or more of the other units. Lock apparatus is provided in the shareable unit to allow a first unit to lock the shareable unit so that no other unit attempting to lock the shareable unit will be permitted access to the shareable unit. The lock apparatus includes means that permit two units desiring to lock the shareable unit to make simultaneously asynchronous requests to lock the shareable unit. The lock apparatus further includes means to permit the unit which has locked the shareable unit to unlock the shareable unit so that it becomes available for a subsequent lock by a unit. The lock apparatus also includes means to allow the shared unit to be accessed by other units not attempting to lock the shareable unit even when the shareable unit is locked.