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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 1.5 2006/06/29 19:56:19 swildner Exp $
39 .Nd "lockmgr family of functions"
44 .Fn lockinit "struct lock *lkp" "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"
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.
66 This is used for both debugging output and
69 The timeout value passed to
72 The flags the lock is to be initialized with.
73 .Bl -tag -width ".Dv LG_CANRECURSE"
75 Do not sleep while acquiring the lock.
79 Allow recursive exclusive locks.
81 Disable the spinlock while acquiring the lock.
85 during a sleep; otherwise, 0 is used.
91 function returns a count of the number of exclusive locks and shared locks
97 function is a non-blocking counter-part of
99 which, can be safely used in assertion statements e.g. a
104 function handles general locking functionality within the kernel, including
105 support for shared and exclusive locks, and recursion.
107 is also able to upgrade and downgrade locks.
110 .Bl -tag -width ".Fa flags"
112 A pointer to the lock to manipulate.
114 Flags indicating what action is to be taken.
115 .Bl -tag -width ".Dv LK_EXCLUPGRADE"
117 Acquire a shared lock.
118 If an exclusive lock is currently held, it will be downgraded.
120 Acquire an exclusive lock.
121 If an exclusive lock is already held, and
123 is not set, the system will
126 Downgrade exclusive lock to a shared lock.
127 Downgrading a shared lock is not permitted.
128 If an exclusive lock has been recursed, all references will be downgraded.
129 .It Dv LK_EXCLUPGRADE
130 Upgrade a shared lock to an exclusive lock.
133 if there is someone ahead of you in line waiting for an upgrade.
134 If this call fails, the shared lock is lost.
135 Attempts to upgrade an exclusive lock will cause a
138 Upgrade a shared lock to an exclusive lock.
139 If this call fails, the shared lock is lost.
140 Attempts to upgrade an exclusive lock will cause a
144 Releasing a lock that is not held can cause a
147 Fail if operation has slept.
149 Do not allow the call to sleep.
150 This can be used to test the lock.
152 Allow recursion on an exclusive lock.
153 For every lock there must be a release.
159 function returns the status of the lock in relation to the
166 and an exclusive lock is held,
171 .Fn lockmgr_printinfo
172 function prints debugging information about the lock.
173 It is used primarily by
179 function returns an integer greater than or equal to zero.
183 function returns 0 on success and non-zero on failure.
188 .Bl -tag -width ".Dv LK_EXCLUSIVE"
190 An exclusive lock is held by the thread
193 An exclusive lock is held by someone other than the thread
196 A shared lock is held.
198 The lock is not held by anyone.
206 was set, and a sleep would have been required.
214 was set in the lock priority, and a signal was delivered during a sleep.
220 was set in the lock priority, a signal was delivered during a sleep,
221 and the system call is to be restarted.
222 .It Bq Er EWOULDBLOCK
223 a non-zero timeout was given, and the timeout expired.
226 Upgrade attempts that fail result in the loss of the lock that
228 Also, it is invalid to upgrade an
229 exclusive lock, and a
231 will be the result of trying.
237 This man page was written by
238 .An Chad David Aq davidc@acns.ab.ca .