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27 .\" $FreeBSD: src/share/man/man9/lock.9,v 1.11 2003/09/08 19:57:21 ru Exp $
37 .Nm lockmgr_printinfo ,
39 .Nd "lockmgr family of functions"
44 .Fn lockinit "struct lock *lkp" "const char *wmesg" "int timo" "int flags"
46 .Fn lockuninit "struct lock *lkp"
48 .Fn lockcount "struct lock *lkp"
50 .Fn lockcountnb "struct lock *lkp"
52 .Fn lockmgr "struct lock *lkp" "u_int flags"
54 .Fn lockstatus "struct lock *lkp" "struct thread *td"
56 .Fn lockmgr_printinfo "struct lock *lkp"
58 .Fn lockowned "struct lock *lkp"
62 function is used to initialize a lock.
63 It must be called before any operation can be performed on a lock.
65 .Bl -tag -width ".Fa wmesg"
67 A pointer to the lock to initialize.
70 This is used for both debugging output and
73 The timeout value passed to
76 The flags the lock is to be initialized with.
77 .Bl -tag -width ".Dv LK_CANRECURSE"
79 Do not sleep while acquiring the lock.
83 Allow recursive exclusive locks.
87 during a sleep; otherwise, 0 is used.
93 function destroys a lock that was previously initialized using
98 function returns a count of the number of exclusive locks and shared locks
104 function is a non-blocking counter-part of
106 which, can be safely used in assertion statements e.g. a
111 function handles general locking functionality within the kernel, including
112 support for shared and exclusive locks, and recursion.
114 is also able to upgrade and downgrade locks.
117 .Bl -tag -width ".Fa flags"
119 A pointer to the lock to manipulate.
121 Flags indicating what action is to be taken.
122 .Bl -tag -width ".Dv LK_EXCLUPGRADE"
124 Acquire a shared lock.
125 If an exclusive lock is currently held, it will be downgraded.
127 Acquire an exclusive lock.
128 If an exclusive lock is already held, and
130 is not set, the system will
133 Downgrade exclusive lock to a shared lock.
134 Downgrading a shared lock is not permitted.
135 If an exclusive lock has been recursed, all references will be downgraded.
136 .It Dv LK_EXCLUPGRADE
137 Upgrade a shared lock to an exclusive lock.
140 if there is someone ahead of you in line waiting for an upgrade.
141 If this call fails, the shared lock is lost.
142 Attempts to upgrade an exclusive lock will cause a
145 Upgrade a shared lock to an exclusive lock.
146 If this call fails, the shared lock is lost.
147 Attempts to upgrade an exclusive lock will cause a
151 Releasing a lock that is not held can cause a
154 Fail if operation has slept.
156 Do not allow the call to sleep.
157 This can be used to test the lock.
159 Allow recursion on an exclusive lock.
160 For every lock there must be a release.
166 function returns the status of the lock in relation to the
173 and an exclusive lock is held,
178 .Fn lockmgr_printinfo
179 function prints debugging information about the lock.
180 It is used primarily by
186 function is used to determine whether the calling thread owns a lock.
190 function returns an integer greater than or equal to zero.
194 function returns 0 on success and non-zero on failure.
199 .Bl -tag -width ".Dv LK_EXCLUSIVE"
201 An exclusive lock is held by the thread
204 An exclusive lock is held by someone other than the thread
207 A shared lock is held.
209 The lock is not held by anyone.
214 function returns a non-zero return value if the caller owns the lock shared or exclusive.
216 The lock manager itself is implemented within the file
217 .Pa /sys/kern/kern_lock.c .
218 Data structures and function prototypes for the lock manager are in
219 .Pa /sys/sys/lock.h .
226 was set, and a sleep would have been required.
234 was set in the lock priority, and a signal was delivered during a sleep.
240 was set in the lock priority, a signal was delivered during a sleep,
241 and the system call is to be restarted.
242 .It Bq Er EWOULDBLOCK
243 a non-zero timeout was given, and the timeout expired.
246 Upgrade attempts that fail result in the loss of the lock that
248 Also, it is invalid to upgrade an
249 exclusive lock, and a
251 will be the result of trying.
258 The lock manager appeared in
261 The lock manager API first appeared in
264 This man page was written by
265 .An Chad David Aq Mt davidc@acns.ab.ca .