lockcount.9freebsd

Langue: en

Version: 309420 (debian - 07/07/09)

Section: 9 (Appels noyau Linux)


BSD mandoc

NAME

lockinit lockdestroy lockcount lockmgr lockstatus lockmgr_printinfo - lockmgr family of functions

SYNOPSIS

In sys/types.h In sys/lock.h In sys/lockmgr.h Ft void Fn lockinit struct lock *lkp int prio const char *wmesg int timo int flags Ft void Fn lockdestroy struct lock *lkp Ft int Fn lockcount struct lock *lkp Ft int Fn lockmgr struct lock *lkp u_int flags struct mtx *interlkp struct thread *td Ft int Fn lockstatus struct lock *lkp struct thread *td Ft void Fn lockmgr_printinfo struct lock *lkp

DESCRIPTION

The Fn lockinit function is used to initialize a lock. It must be called before any operation can be performed on a lock. Its arguments are:
Fa lkp
A pointer to the lock to initialize.
Fa prio
The priority passed to sleep(9).
Fa wmesg
The lock message. This is used for both debugging output and sleep(9).
Fa timo
The timeout value passed to sleep(9).
Fa flags
The flags the lock is to be initialized with.
LK_NOWAIT
Do not sleep while acquiring the lock.
LK_SLEEPFAIL
Fail after a sleep.
LK_CANRECURSE
Allow recursive exclusive locks.
LK_NOSHARE
Allow exclusive locks only.
LK_TIMELOCK
Use Fa timo during a sleep; otherwise, 0 is used.

The Fn lockdestroy function is used to destroy a lock, and while it is called in a number of places in the kernel, it currently does nothing.

The Fn lockcount function returns a count of the number of exclusive locks and shared locks held against the lock Fa lkp .

The Fn lockmgr function handles general locking functionality within the kernel, including support for shared and exclusive locks, and recursion. Fn lockmgr is also able to upgrade and downgrade locks.

Its arguments are:

Fa lkp
A pointer to the lock to manipulate.
Fa flags
Flags indicating what action is to be taken.
LK_SHARED
Acquire a shared lock. If an exclusive lock is currently held, it will be downgraded.
LK_EXCLUSIVE
Acquire an exclusive lock. If an exclusive lock is already held, and LK_CANRECURSE is not set, the system will panic(9).
LK_DOWNGRADE
Downgrade exclusive lock to a shared lock. Downgrading a shared lock is not permitted. If an exclusive lock has been recursed, all references will be downgraded.
LK_EXCLUPGRADE
Upgrade a shared lock to an exclusive lock. Fails with Er EBUSY if there is someone ahead of you in line waiting for an upgrade. If this call fails, the shared lock is lost. Attempts to upgrade an exclusive lock will cause a panic(9).
LK_UPGRADE
Upgrade a shared lock to an exclusive lock. If this call fails, the shared lock is lost. During the upgrade, the shared lock could be temporarily dropped. Attempts to upgrade an exclusive lock will cause a panic(9).
LK_RELEASE
Release the lock. Releasing a lock that is not held can cause a panic(9).
LK_DRAIN
Wait for all activity on the lock to end, then mark it decommissioned. This is used before freeing a lock that is part of a piece of memory that is about to be freed. (As documented in In sys/lockmgr.h . )
LK_SLEEPFAIL
Fail if operation has slept.
LK_NOWAIT
Do not allow the call to sleep. This can be used to test the lock.
LK_CANRECURSE
Allow recursion on an exclusive lock. For every lock there must be a release.
LK_INTERLOCK
Unlock the interlock (which should be locked already).
Fa interlkp
An interlock mutex for controlling group access to the lock. If LK_INTERLOCK is specified, Fn lockmgr assumes Fa interlkp is currently owned and not recursed, and will return it unlocked. See mtx_assert9.
Fa td
A thread responsible for this call. NULL becomes LK_KERNPROC

The Fn lockstatus function returns the status of the lock in relation to the Vt thread passed to it. Note that if Fa td is NULL and an exclusive lock is held, LK_EXCLUSIVE will be returned.

The Fn lockmgr_printinfo function prints debugging information about the lock. It is used primarily by VOP_PRINT9 functions.

RETURN VALUES

The Fn lockcount function returns an integer greater than or equal to zero.

The Fn lockmgr function returns 0 on success and non-zero on failure.

The Fn lockstatus function returns:

LK_EXCLUSIVE
An exclusive lock is held by the thread Fa td .
LK_EXCLOTHER
An exclusive lock is held by someone other than the thread Fa td .
LK_SHARED
A shared lock is held.
0
The lock is not held by anyone.

ERRORS

Fn lockmgr fails if:
Bq Er EBUSY
LK_FORCEUPGRADE was requested and another thread had already requested a lock upgrade.
Bq Er EBUSY
LK_NOWAIT was set, and a sleep would have been required.
Bq Er ENOLCK
LK_SLEEPFAIL was set and Fn lockmgr did sleep.
Bq Er EINTR
PCATCH was set in the lock priority, and a signal was delivered during a sleep. Note the Er ERESTART error below.
Bq Er ERESTART
PCATCH was set in the lock priority, a signal was delivered during a sleep, and the system call is to be restarted.
Bq Er EWOULDBLOCK
a non-zero timeout was given, and the timeout expired.

LOCKS

If LK_INTERLOCK is passed in the Fa flags argument to Fn lockmgr , the Fa interlkp must be held prior to calling Fn lockmgr , and will be returned unlocked.

Upgrade attempts that fail result in the loss of the lock that is currently held. Also, it is invalid to upgrade an exclusive lock, and a panic(9) will be the result of trying.

SEE ALSO

condvar(9), locking(9), mutex(9), rwlock(9), sleep(9), sx(9), mtx_assert9, panic(9), VOP_PRINT9

AUTHORS

This manual page was written by An Chad David Aq davidc@acns.ab.ca .