m4_comment([$Id: stdmode.so,v 10.26 2001/05/22 19:39:32 bostic Exp $])m4_ref_title(Locking Subsystem,    Standard lock modes, standard @lock modes, lock/max, lock/dead)m4_p([dnlThe m4_db locking protocol is described by a conflict matrix.  Aconflict matrix is an NxN array in which N is the number of differentlock modes supported, and the (i, j)th entry of the array indicateswhether a lock of mode i conflicts with a lock of mode j.  In addition,m4_db defines the type m4_arg(db_lockmode_t), which is the type of alock mode within a conflict matrix.])m4_p([dnlThe following is an example of a conflict matrix.  The actual conflictmatrix used by m4_db to support the underlying access methods is morecomplicated, but this matrix shows the lock mode relationships availableto applications using the m4_db Locking subsystem interfaces directly.])m4_tagbeginm4_tag(DB_LOCK_NG, [not granted (always 0)])m4_tagns(DB_LOCK_READ, [read (shared)])m4_tagns(DB_LOCK_WRITE, [write (exclusive)])m4_tagns(DB_LOCK_IWRITE, [intention to write (shared)])m4_tagns(DB_LOCK_IREAD, [intention to read (shared)])m4_tagns(DB_LOCK_IWR, [intention to read and write (shared)])m4_tagendm4_p([dnlIn a conflict matrix, the rows indicate the lock that is held, and thecolumns indicate the lock that is requested.  A 1 represents a conflict(that is, do not grant the lock if the indicated lock is held), and a0 indicates that it is OK to grant the lock.])m4_indent([dnl		Notheld	Read    Write	IWrite	IRead	IRWNotheld		0	0	0	0	0	0Read*		0	0	1	1	0	1Write**		0	1	1	1	1	1Intent Write	0	1	1	0	0	0Intent Read	0	0	1	0	0	0Intent RW	0	1	1	0	0	0])m4_tagbeginm4_tag(*, [dnlIn this case, suppose that there is a read lock held on an object.  A newrequest for a read lock would be granted, but a request for a write lockwould not.])m4_tag(**, [dnlIn this case, suppose that there is a write lock held on an object.  Anew request for either a read or write lock would be denied.])m4_tagendm4_page_footer