2 .\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice(s), this list of conditions and the following disclaimer as
9 .\" the first lines of this file unmodified other than the possible
10 .\" addition of one or more copyright notices.
11 .\" 2. Redistributions in binary form must reproduce the above copyright
12 .\" notice(s), this list of conditions and the following disclaimer in the
13 .\" documentation and/or other materials provided with the distribution.
15 .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
16 .\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 .\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
19 .\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
20 .\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 .\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 .\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
27 .\" $FreeBSD: src/share/man/man9/lock.9,v 1.11 2003/09/08 19:57:21 ru Exp $
38 .Nd "lockmgr family of functions"
43 .Fn lockinit "struct lock *lkp" "const char *wmesg" "int timo" "int flags"
45 .Fn lockuninit "struct lock *lkp"
47 .Fn lockcount "struct lock *lkp"
49 .Fn lockcountnb "struct lock *lkp"
51 .Fn lockmgr "struct lock *lkp" "u_int flags"
53 .Fn lockstatus "struct lock *lkp" "struct thread *td"
55 .Fn lockmgr_printinfo "struct lock *lkp"
59 function is used to initialize a lock.
60 It must be called before any operation can be performed on a lock.
62 .Bl -tag -width ".Fa wmesg"
64 A pointer to the lock to initialize.
67 This is used for both debugging output and
70 The timeout value passed to
73 The flags the lock is to be initialized with.
74 .Bl -tag -width ".Dv LK_CANRECURSE"
76 Do not sleep while acquiring the lock.
80 Allow recursive exclusive locks.
84 during a sleep; otherwise, 0 is used.
90 function destroys a lock that was previously initialized using
95 function returns a count of the number of exclusive locks and shared locks
101 function is a non-blocking counter-part of
103 which, can be safely used in assertion statements e.g. a
108 function handles general locking functionality within the kernel, including
109 support for shared and exclusive locks, and recursion.
111 is also able to upgrade and downgrade locks.
114 .Bl -tag -width ".Fa flags"
116 A pointer to the lock to manipulate.
118 Flags indicating what action is to be taken.
119 .Bl -tag -width ".Dv LK_EXCLUPGRADE"
121 Acquire a shared lock.
122 If an exclusive lock is currently held, it will be downgraded.
124 Acquire an exclusive lock.
125 If an exclusive lock is already held, and
127 is not set, the system will
130 Downgrade exclusive lock to a shared lock.
131 Downgrading a shared lock is not permitted.
132 If an exclusive lock has been recursed, all references will be downgraded.
133 .It Dv LK_EXCLUPGRADE
134 Upgrade a shared lock to an exclusive lock.
137 if there is someone ahead of you in line waiting for an upgrade.
138 If this call fails, the shared lock is lost.
139 Attempts to upgrade an exclusive lock will cause a
142 Upgrade a shared lock to an exclusive lock.
143 If this call fails, the shared lock is lost.
144 Attempts to upgrade an exclusive lock will cause a
148 Releasing a lock that is not held can cause a
151 Fail if operation has slept.
153 Do not allow the call to sleep.
154 This can be used to test the lock.
156 Allow recursion on an exclusive lock.
157 For every lock there must be a release.
163 function returns the status of the lock in relation to the
170 and an exclusive lock is held,
175 .Fn lockmgr_printinfo
176 function prints debugging information about the lock.
177 It is used primarily by
183 function returns an integer greater than or equal to zero.
187 function returns 0 on success and non-zero on failure.
192 .Bl -tag -width ".Dv LK_EXCLUSIVE"
194 An exclusive lock is held by the thread
197 An exclusive lock is held by someone other than the thread
200 A shared lock is held.
202 The lock is not held by anyone.
205 The lock manager itself is implemented within the file
206 .Pa /sys/kern/kern_lock.c .
207 Data structures and function prototypes for the lock manager are in
208 .Pa /sys/sys/lock.h .
215 was set, and a sleep would have been required.
223 was set in the lock priority, and a signal was delivered during a sleep.
229 was set in the lock priority, a signal was delivered during a sleep,
230 and the system call is to be restarted.
231 .It Bq Er EWOULDBLOCK
232 a non-zero timeout was given, and the timeout expired.
235 Upgrade attempts that fail result in the loss of the lock that
237 Also, it is invalid to upgrade an
238 exclusive lock, and a
240 will be the result of trying.
246 The lock manager appeared in
249 The lock manager API first appeared in
252 This man page was written by
253 .An Chad David Aq davidc@acns.ab.ca .