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39 .Nm lockmgr_printinfo ,
40 .Nm lockmgr_recursed ,
45 .Nd "lockmgr family of functions"
51 .Fn lockinit "struct lock *lkp" "int prio" "const char *wmesg" "int timo" "int flags"
53 .Fn lockdestroy "struct lock *lkp"
55 .Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *ilk"
57 .Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *ilk" "const char *wmesg" "int prio" "int timo"
59 .Fn lockmgr_args_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk" "const char *wmesg" "int prio" "int timo"
61 .Fn lockmgr_disown "struct lock *lkp"
63 .Fn lockmgr_printinfo "const struct lock *lkp"
65 .Fn lockmgr_recursed "const struct lock *lkp"
67 .Fn lockmgr_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk"
69 .Fn lockmgr_waiters "const struct lock *lkp"
71 .Fn lockstatus "const struct lock *lkp"
73 .Cd "options INVARIANTS"
74 .Cd "options INVARIANT_SUPPORT"
76 .Fn lockmgr_assert "const struct lock *lkp" "int what"
80 function is used to initialize a lock.
81 It must be called before any operation can be performed on a lock.
83 .Bl -tag -width ".Fa wmesg"
85 A pointer to the lock to initialize.
87 The priority passed to
91 This is used for both debugging output and
94 The timeout value passed to
97 The flags the lock is to be initialized with:
98 .Bl -tag -width ".Dv LK_CANRECURSE"
100 Enable adaptive spinning for this lock if the kernel is compiled with the
101 ADAPTIVE_LOCKMGRS option.
103 Allow recursive exclusive locks.
105 Disable lock profiling for this lock.
107 Allow exclusive locks only.
114 should log messages about duplicate locks being acquired.
118 logging for this lock.
122 during a sleep; otherwise, 0 is used.
128 function is used to destroy a lock, and while it is called in a number of
129 places in the kernel, it currently does nothing.
135 functions handle general locking functionality within the kernel, including
136 support for shared and exclusive locks, and recursion.
140 are also able to upgrade and downgrade locks.
143 .Bl -tag -width ".Fa flags"
145 A pointer to the lock to manipulate.
147 Flags indicating what action is to be taken.
148 .Bl -tag -width ".Dv LK_NODDLKTREAT"
150 Acquire a shared lock.
151 If an exclusive lock is currently held,
155 Acquire an exclusive lock.
156 If an exclusive lock is already held, and
158 is not set, the system will
161 Downgrade exclusive lock to a shared lock.
162 Downgrading a shared lock is not permitted.
163 If an exclusive lock has been recursed, the system will
166 Upgrade a shared lock to an exclusive lock.
167 If this call fails, the shared lock is lost, even if the
170 During the upgrade, the shared lock could
171 be temporarily dropped.
172 Attempts to upgrade an exclusive lock will cause a
175 Try to upgrade a shared lock to an exclusive lock.
176 The failure to upgrade does not result in the dropping
177 of the shared lock ownership.
180 Releasing a lock that is not held can cause a
183 Wait for all activity on the lock to end, then mark it decommissioned.
184 This is used before freeing a lock that is part of a piece of memory that is
187 .In sys/lockmgr.h . )
189 Fail if operation has slept.
191 Do not allow the call to sleep.
192 This can be used to test the lock.
196 checks for this instance.
198 Allow recursion on an exclusive lock.
199 For every lock there must be a release.
201 Unlock the interlock (which should be locked already).
202 .It Dv LK_NODDLKTREAT
205 postpones serving further shared requests for shared-locked lock if there is
206 exclusive waiter, to avoid exclusive lock starvation.
207 But, if the thread requesting the shared lock already owns a shared lockmgr
208 lock, the request is granted even in presence of the parallel exclusive lock
209 request, which is done to avoid deadlocks with recursive shared acquisition.
213 flag can only be used by code which requests shared non-recursive lock.
214 The flag allows exclusive requests to preempt the current shared request
215 even if the current thread owns shared locks.
216 This is safe since shared lock is guaranteed to not recurse, and is used
217 when thread is known to held unrelated shared locks, to not cause
218 unnecessary starvation. An example is
227 An interlock mutex for controlling group access to the lock.
236 is currently owned and not recursed, and will return it unlocked.
254 on a per-instance basis.
255 The specified values will override the default
256 ones, but this can still be used passing, respectively,
257 .Dv LK_WMESG_DEFAULT ,
260 .Dv LK_TIMO_DEFAULT .
264 function switches the owner from the current thread to be
266 if the lock is already held.
269 .Fn lockmgr_printinfo
270 function prints debugging information about the lock.
271 It is used primarily by
277 function returns true if the lock is recursed, 0
282 function returns true if the lock has waiters, 0 otherwise.
286 function returns the status of the lock in relation to the current thread.
289 .Cd "options INVARIANTS"
291 .Cd "options INVARIANT_SUPPORT" ,
296 for the assertions specified in
298 and panics if they are not met.
299 One of the following assertions must be specified:
300 .Bl -tag -width ".Dv KA_UNLOCKED"
302 Assert that the current thread has either a shared or an exclusive lock on the
304 lock pointed to by the first argument.
306 Assert that the current thread has a shared lock on the
308 lock pointed to by the first argument.
310 Assert that the current thread has an exclusive lock on the
312 lock pointed to by the first argument.
314 Assert that the current thread has no lock on the
316 lock pointed to by the first argument.
319 In addition, one of the following optional assertions can be used with
326 .Bl -tag -width ".Dv KA_NOTRECURSED"
328 Assert that the current thread has a recursed lock on
330 .It Dv KA_NOTRECURSED
331 Assert that the current thread does not have a recursed lock on
339 functions return 0 on success and non-zero on failure.
344 .Bl -tag -width ".Dv LK_EXCLUSIVE"
346 An exclusive lock is held by the current thread.
348 An exclusive lock is held by someone other than the current thread.
350 A shared lock is held.
352 The lock is not held by anyone.
362 was requested and another thread had already requested a lock upgrade.
365 was set, and a sleep would have been required, or
367 operation was not able to upgrade the lock.
377 was set in the lock priority, and a signal was delivered during a sleep.
383 was set in the lock priority, a signal was delivered during a sleep,
384 and the system call is to be restarted.
385 .It Bq Er EWOULDBLOCK
386 a non-zero timeout was given, and the timeout expired.
399 must be held prior to calling
403 and will be returned unlocked.
405 Upgrade attempts that fail result in the loss of the lock that
407 Also, it is invalid to upgrade an
408 exclusive lock, and a
410 will be the result of trying.
422 This manual page was written by
423 .An Chad David Aq davidc@acns.ab.ca .