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typedef PtLockMode

typedef PtLockMode

Lock modes are used to specify locks and to report on the locks which have been set. PtLockMode is actually just a typedef:

typedef word PtLockMode;

The following tablelists all possible values for PtLockMode, summarizes the read/write/delete restrictions imposed by each lock type, and shows the operations guaranteed to the locking process:

Lock Mode	Guarantees for my process	Restrictions for other processes
PtLK_NONE	none	none
PtLK_READvDELETE	read	can't delete
PtLK_READvWRITE	read	can't write or delete
PtLK_WRITEvWRITE	read, write	can't write or delete
PtLK_DELETEvWRITE	read, write, delete	can't write, or delete
PtLK_DELETEvREAD	read, write, delete	can't read, write, or delete
PtLK_EXCLUSIVE	read, write, delete	can't read, write, or delete
transaction write lock	read, write	can't write or delete
transaction delete lock	read, write, delete	can't write or delete

You can lock an object that is already locked as long as your lock does not interfere with the purpose of any existing lock. The following table shows the locks which may be set if other locks already exist:

Current Lock	RvD	RvW	WvW	DvW	DvR	EXC
PtLK_NONE	OK	OK	OK	OK	OK	OK
PtLK_READvDELETE	OK	OK	OK	fails	fails	fails
PtLK_READvWRITE	OK	OK	fails	fails	fails	fails
PtLK_WRITEvWRITE	OK	fails	fails	fails	fails	fails
PtLK_DELETEvWRITE	fails	fails	fails	fails	fails	fails
PtLK_DELETEvREAD	fails	fails	fails	fails	fails	fails
PtLK_EXCLUSIVE	fails	fails	fails	fails	fails	fails
transaction write lock	OK	fails	fails	fails	fails	fails
transaction delete lock	fails	fails	fails	fails	fails	fails

Since exclusive access implies that you are the only person who has an object, PtLK_EXCLUSIVE will fail if another process already has the object in memory.

Copyright (c) 1996 POET Software, Inc. All rights reserved. Reproduction in whole or in part in any form or medium without the express permission of POET Software, Inc. is prohibited.