Importance

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Abstract

A flexible, low cost range locking mechanism allows a process requesting a lock to place a lock upon any requested range within a resource of a computer system. Various processes may hold locks upon different ranges of a resource simultaneously. A particular range may also be locked by different processes that are able to share the range. A sub-lock represents a unique range of the resource and has begin and end points that identify that portion of the requested range to which the sub-lock corresponds. A locked range may include numerous sub-locks. Each sub-lock has a mode indicating whether the sub-lock represents a shared lock, an exclusive lock or other. Sub-locks also have an incremental counter indicating the number of processes that hold a read lock upon a region, a flag to indicate whether a process is waiting to lock the region, a queue for listing waiting processes and other attributes. Sub-locks are stored in a data structure sequentially in the order in which they occur within the resource to facilitate searching. A range of a resource that is locked by one or more processes is indicated by setting the incremental counter of the sub-lock corresponding to that range to the number of processes that share the range. A requested range that either begins or ends within a previously locked region may result in the region being split into two distinct and contiguous regions, each region having a corresponding sub-lock. A range beginning and ending within a locked region splits the region into three regions.

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First Claim