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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 lockmgr "struct lock *lkp" "u_int flags"
50 .Fn lockmgr_try "struct lock *lkp" "u_int flags"
52 .Fn lockstatus "struct lock *lkp" "struct thread *td"
54 .Fn lockmgr_printinfo "struct lock *lkp"
56 .Fn lockowned "struct lock *lkp"
60 function is used to initialize a lock.
61 It must be called before any operation can be performed on a lock.
63 .Bl -tag -width ".Fa wmesg"
65 A pointer to the lock to initialize.
68 This is used for both debugging output and
71 The timeout value passed to
74 The flags the lock is to be initialized with.
75 .Bl -tag -width ".Dv LK_CANRECURSE"
77 Do not sleep while acquiring the lock.
81 Allow recursive exclusive locks.
85 during a sleep; otherwise, 0 is used.
91 function destroys a lock that was previously initialized using
96 function handles general locking functionality within the kernel, including
97 support for shared and exclusive locks, and recursion.
99 is also able to upgrade and downgrade locks.
102 .Bl -tag -width ".Fa flags"
104 A pointer to the lock to manipulate.
106 Flags indicating what action is to be taken.
107 .Bl -tag -width ".Dv LK_EXCLUPGRADE"
109 Acquire a shared lock.
110 If an exclusive lock is currently held, it will be downgraded.
112 Acquire an exclusive lock.
113 If an exclusive lock is already held, and
115 is not set, the system will
118 Downgrade exclusive lock to a shared lock.
119 Downgrading a shared lock is not permitted.
120 If an exclusive lock has been recursed, all references will be downgraded.
121 .It Dv LK_EXCLUPGRADE
122 Upgrade a shared lock to an exclusive lock.
125 if there is someone ahead of you in line waiting for an upgrade.
126 If this call fails for any reason, the shared lock is lost.
127 Attempts to upgrade an exclusive lock not already
128 owned by the caller will cause a
130 but otherwise will always succeed.
131 NOTE! When this operation succeeds, it guarantees that no other
132 exclusive lock was able to acquire the lock ahead of you, but
133 as indicated above, if it fails your current shared lock is lost.
135 Upgrade a shared lock to an exclusive lock.
136 If this call fails for any reason, the shared lock is lost.
137 Attempts to upgrade an exclusive lock not already
138 owned by the caller will cause a
140 but otherwise will always succeed.
141 WARNING! This operation can block with the current lock temporarily
142 released, and other exclusive or shared lock holders can inject before
143 the lock is acquired on your behalf.
146 Releasing a lock that is not held can cause a
149 Fail if operation has slept.
151 Do not allow the call to sleep.
152 This can be used to test the lock.
154 Allow recursion on an exclusive lock.
155 For every lock there must be a release.
161 function is similar to
163 but it will not sleep and returns
165 if the lock was successfully obtained and
171 function returns the status of the lock in relation to the
178 and an exclusive lock is held,
183 .Fn lockmgr_printinfo
184 function prints debugging information about the lock.
185 It is used primarily by
191 function is used to determine whether the calling thread owns a lock.
195 function returns 0 on success and non-zero on failure.
200 .Bl -tag -width ".Dv LK_EXCLUSIVE"
202 An exclusive lock is held by the thread
205 An exclusive lock is held by someone other than the thread
208 A shared lock is held.
210 The lock is not held by anyone.
215 function returns a non-zero return value if the caller owns the lock shared or exclusive.
217 The lock manager itself is implemented within the file
218 .Pa /sys/kern/kern_lock.c .
219 Data structures and function prototypes for the lock manager are in
220 .Pa /sys/sys/lock.h .
227 was set, and a sleep would have been required.
235 was set in the lock priority, and a signal was delivered during a sleep.
241 was set in the lock priority, a signal was delivered during a sleep,
242 and the system call is to be restarted.
243 .It Bq Er EWOULDBLOCK
244 a non-zero timeout was given, and the timeout expired.
247 Upgrade attempts that fail result in the loss of the lock that
249 Also, it is invalid to upgrade an
250 exclusive lock, and a
252 will be the result of trying.
259 The lock manager appeared in
262 The lock manager API first appeared in
265 This man page was written by
266 .An Chad David Aq Mt davidc@acns.ab.ca .