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27 .\" $FreeBSD: src/share/man/man9/lock.9,v 1.11 2003/09/08 19:57:21 ru Exp $
28 .\" $DragonFly: src/share/man/man9/lock.9,v 1.4 2006/04/23 16:23:12 swildner Exp $
39 .Nd "lockmgr family of functions"
44 .Fn lockinit "struct lock *lkp" "int prio" "char *wmesg" "int timo" "int flags"
46 .Fn lockcount "struct lock *lkp"
48 .Fn lockcountnb "struct lock *lkp"
50 .Fn lockmgr "struct lock *lkp" "u_int flags" "struct thread *td"
52 .Fn lockstatus "struct lock *lkp" "struct thread *td"
54 .Fn lockmgr_printinfo "struct lock *lkp"
58 function is used to initialize a lock.
59 It must be called before any operation can be performed on a lock.
61 .Bl -tag -width ".Fa wmesg"
63 A pointer to the lock to initialize.
65 The priority passed to
69 This is used for both debugging output and
72 The timeout value passed to
75 The flags the lock is to be initialized with.
76 .Bl -tag -width ".Dv LG_CANRECURSE"
78 Do not sleep while acquiring the lock.
82 Allow recursive exclusive locks.
84 Disable the spinlock while acquiring the lock.
88 during a sleep; otherwise, 0 is used.
94 function returns a count of the number of exclusive locks and shared locks
100 function is a non-blocking counter-part of
102 which, can be safely used in assertion statements e.g. a
107 function handles general locking functionality within the kernel, including
108 support for shared and exclusive locks, and recursion.
110 is also able to upgrade and downgrade locks.
113 .Bl -tag -width ".Fa flags"
115 A pointer to the lock to manipulate.
117 Flags indicating what action is to be taken.
118 .Bl -tag -width ".Dv LK_EXCLUPGRADE"
120 Acquire a shared lock.
121 If an exclusive lock is currently held, it will be downgraded.
123 Acquire an exclusive lock.
124 If an exclusive lock is already held, and
126 is not set, the system will
129 Downgrade exclusive lock to a shared lock.
130 Downgrading a shared lock is not permitted.
131 If an exclusive lock has been recursed, all references will be downgraded.
132 .It Dv LK_EXCLUPGRADE
133 Upgrade a shared lock to an exclusive lock.
136 if there is someone ahead of you in line waiting for an upgrade.
137 If this call fails, the shared lock is lost.
138 Attempts to upgrade an exclusive lock will cause a
141 Upgrade a shared lock to an exclusive lock.
142 If this call fails, the shared lock is lost.
143 Attempts to upgrade an exclusive lock will cause a
147 Releasing a lock that is not held can cause a
150 Fail if operation has slept.
152 Do not allow the call to sleep.
153 This can be used to test the lock.
155 Allow recursion on an exclusive lock.
156 For every lock there must be a release.
159 A thread responsible for this call.
167 function returns the status of the lock in relation to the
174 and an exclusive lock is held,
179 .Fn lockmgr_printinfo
180 function prints debugging information about the lock.
181 It is used primarily by
187 function returns an integer greater than or equal to zero.
191 function returns 0 on success and non-zero on failure.
196 .Bl -tag -width ".Dv LK_EXCLUSIVE"
198 An exclusive lock is held by the thread
201 An exclusive lock is held by someone other than the thread
204 A shared lock is held.
206 The lock is not held by anyone.
214 was set, and a sleep would have been required.
222 was set in the lock priority, and a signal was delivered during a sleep.
228 was set in the lock priority, a signal was delivered during a sleep,
229 and the system call is to be restarted.
230 .It Bq Er EWOULDBLOCK
231 a non-zero timeout was given, and the timeout expired.
234 Upgrade attempts that fail result in the loss of the lock that
236 Also, it is invalid to upgrade an
237 exclusive lock, and a
239 will be the result of trying.
245 This man page was written by
246 .An Chad David Aq davidc@acns.ab.ca .