Commit Graph

4 Commits

Author SHA1 Message Date
John Baldwin
3f08bd8bce Add a basic reader/writer lock implementation to the kernel. This
implementation is by no means perfect as far as some of the algorithms
that it uses and the fact that it is missing some functionality (try
locks and upgrades/downgrades are not there yet), however it does seem
to work in my local testing.  There is more detail in the comments in the
code, but the short version follows.

A reader/writer lock is very much like a regular mutex: it cannot be held
across a voluntary sleep; it can be acquired in an interrupt thread; if
the lock is held by a writer then the priority of any threads that block
on the lock will be lent to the owner; the simple case lock operations all
are done in a single atomic op.  It also shares some similiarities
with sx locks: it supports reader/writer semantics (multiple readers,
but single writers); readers are allowed to recurse, but writers are not.

We can extend this implementation further by either improving algorithms
or adding new functionality, but this should at least give us a base to
work with now.

Reviewed by:	arch (in theory)
Tested on:	i386 (4 cpu box with a kernel module that used 4 threads
		that randomly chose between read locks and write locks
		that ran w/o panicing for over a day solid.  It usually
		panic'd within a few seconds when there were bugs during
		testing. :)  The kernel module source is available on
		request.)
2006-01-27 23:13:26 +00:00
John Baldwin
25e498b4b0 Always include the lock_classes[] array in the kernel. The
"is it a spinlock" test in mtx_destroy() needs it even in non-debug
kernels.

Reported by:	danfe
2006-01-18 18:02:50 +00:00
John Baldwin
6ef970a972 Bah. Fix 'show lock' to actually be compiled in. I had just fixed this in
p4 but had an older subr_lock.c on the machine I committed to CVS from.
2006-01-17 16:58:32 +00:00
John Baldwin
83a81bcb14 Add a new file (kern/subr_lock.c) for holding code related to struct
lock_obj objects:
- Add new lock_init() and lock_destroy() functions to setup and teardown
  lock_object objects including KTR logging and registering with WITNESS.
- Move all the handling of LO_INITIALIZED out of witness and the various
  lock init functions into lock_init() and lock_destroy().
- Remove the constants for static indices into the lock_classes[] array
  and change the code outside of subr_lock.c to use LOCK_CLASS to compare
  against a known lock class.
- Move the 'show lock' ddb function and lock_classes[] array out of
  kern_mutex.c over to subr_lock.c.
2006-01-17 16:55:17 +00:00