Distributed lock manager: Difference between revisions

Revision as of 02:02, 22 January 2010

Revision as of 16:35, 25 February 2010

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*Null Lock (NL). Indicates interest in the resource, but does not prevent other processes from locking it. It has the advantage that the resource and its [[#Lock value block|lock value block]] are preserved, even when no processes are locking it.

*Concurrent Read (CR). Indicates a desire to read (but not update) the resource. It allows other processes to read or update the resource, but prevents others from having exclusive access to it. This is usually employed on high-level resources, in order that highermore levelsrestrictive of locklocks can be obtained on subordinate resources.

*Concurrent Write (CW). Indicates a desire to read and update the resource. It also allows other processes to read or update the resource, but prevents others from having exclusive access to it. This is also usually employed on high-level resources, in order that highermore levelsrestrictive of locklocks can be obtained on subordinate resources.

*Protected Read (PR). This is the traditional ''share lock'', which indicates a desire to read the resource but prevents other from updating it. Others can however also read the resource.