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Document sx_assert(9).

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John Baldwin 2001-10-23 22:51:59 +00:00
parent 751fc77994
commit 7fe151bee5
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=85392
2 changed files with 33 additions and 1 deletions
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1
share/man/man9/Makefile
View file

@ -169,6 +169,7 @@ MLINKS+=spl.9 splnet.9 spl.9 splsoftclock.9 spl.9 splsofttty.9
MLINKS+=spl.9 splstatclock.9 spl.9 spltty.9 spl.9 splvm.9 spl.9 splx.9 MLINKS+=spl.9 splstatclock.9 spl.9 spltty.9 spl.9 splvm.9 spl.9 splx.9
MLINKS+=store.9 subyte.9 store.9 suswintr.9 store.9 susword.9 store.9 suword.9 MLINKS+=store.9 subyte.9 store.9 suswintr.9 store.9 susword.9 store.9 suword.9
MLINKS+=swi.9 swi_sched.9 swi.9 swi_add.9 MLINKS+=swi.9 swi_sched.9 swi.9 swi_add.9
MLINKS+=sx.9 sx_assert.9
MLINKS+=sx.9 sx_init.9 MLINKS+=sx.9 sx_init.9
MLINKS+=sx.9 sx_destroy.9 MLINKS+=sx.9 sx_destroy.9
MLINKS+=sx.9 sx_slock.9 MLINKS+=sx.9 sx_slock.9

33
share/man/man9/sx.9
View file

@ -40,7 +40,8 @@
.Nm sx_sunlock , .Nm sx_sunlock ,
.Nm sx_xunlock , .Nm sx_xunlock ,
.Nm sx_try_upgrade , .Nm sx_try_upgrade ,
.Nm sx_downgrade .Nm sx_downgrade ,
.Nm sx_assert
.Nd kernel shared/exclusive lock .Nd kernel shared/exclusive lock
.Sh SYNOPSIS .Sh SYNOPSIS
.In sys/param.h .In sys/param.h
@ -67,6 +68,8 @@
.Fn sx_try_upgrade "struct sx *sx" .Fn sx_try_upgrade "struct sx *sx"
.Ft void .Ft void
.Fn sx_downgrade "struct sx *sx" .Fn sx_downgrade "struct sx *sx"
.Ft void
.Fn sx_assert "struct sx *sx" "int what"
.Sh DESCRIPTION .Sh DESCRIPTION
Shared/exclusive locks are used to protect data that are read far more often Shared/exclusive locks are used to protect data that are read far more often
than they are written. than they are written.
@ -116,9 +119,37 @@ will return 0 if the shared lock cannot be upgraded to an exclusive lock
immediately; otherwise the exclusive lock will be acquired and a non-zero value immediately; otherwise the exclusive lock will be acquired and a non-zero value
will be returned. will be returned.
.Pp .Pp
The
.Fn sx_assert
function tests specified conditions and panics if they are not met and the
kernel is compiled with
.Dv INVARIANTS .
The following assertions are supported:
.Bl -tag -width SX_XLOCKED
.It Dv SX_LOCKED
Assert that the current thread has either a shared or an exclusive lock on the
sx lock pointed to by the first argument.
.It Dv SX_SLOCKED
Assert that the current thread has a shared lock on the sx lock pointed to by
the first argument.
.It Dv SX_XLOCKED
Assert that the current thread has an exclusive lock on the sx lock pointed to
by the first argument.
.El
.Pp
A thread may not own a shared lock and an exclusive lock simultaneously; A thread may not own a shared lock and an exclusive lock simultaneously;
attempting to do so will result in deadlock. attempting to do so will result in deadlock.
.Sh SEE ALSO .Sh SEE ALSO
.Xr condvar 9 , .Xr condvar 9 ,
.Xr mutex 9 , .Xr mutex 9 ,
.Xr sema 9 .Xr sema 9
.Sh BUGS
Currently there is no way to assert that a lock is not held.
This is not possible in the non-WITNESS case for asserting that this thread
does not hold a shared lock.
In the non-WITNESS case, the
.Dv SX_LOCKED
and
.Dv SX_SLOCKED
assertions merely check that some thread holds a shared lock.
They do not ensure that the current thread holds a shared lock.