Category : Files from Magazines
Archive   : OCT91.ZIP
Filename : 2N10018A

TITLE SPINLOCK - Spinlock Package for MP-Aware C Programs.

;*** SPINLOCK - Spinlock Package for MP-Aware C Programs.
;
; FUNCTIONAL DESCRIPTION.
; This module is assembled to create an OBJ file that can be linked
; with a large model C-language program to provide MP-aware spinlock
; support.
;
; MODIFICATION HISTORY.
; S. E. Jones 91/04/05. Original.
;
; NOTICE: This code is hereby delivered to the public domain.
;
; BUILD ENVIRONMENT.
; MASM 5.10, no special switches.

include spinlock.inc ; spinlock macros.

DefProc MACRO rtn ; macro used to define procedures.
PUBLIC rtn
rtn PROC FAR
ENDM

EndProc MACRO rtn ; macro used to end procedures.
ret
rtn ENDP
ENDM

SPINLOCK SEGMENT PARA PUBLIC 'CODE'

;*** _AllocateSpinLock - Initialize Storage Area as Spinlock Object.
;
; FUNCTIONAL DESCRIPTION.
; This routine is called by large-model C routines to initialize
; a word of storage as a spinlock object. The lock is set to the
; released state. A return code is architected, even though it
; is not used in this particular package. If the package is
; changed to support spinlocks that are managed purely inside
; the private part of this package, then it might be possible
; to run out of handles to spinlocks.
;
; ENTRY.
; [bp+6,bp+8] - FWA, word of storage to format as spinlock object.
;
; EXIT.
; AX - 0 if success, else nonzero if failure.
;
; USES.
; none.

ASSUME CS:SPINLOCK, DS:NOTHING, ES:NOTHING, SS:NOTHING
DefProc _AllocateSpinLock
push bp
mov bp, sp
push si
push ds
lds si, [bp+6] ; (DS:SI) = FWA, storage.
AllocateSpinLock <[si]> ; initialize the lock.
sub ax, ax ; (AX) = 0, meaning success.
pop ds
pop si
pop bp
EndProc _AllocateSpinLock

;*** _DeallocateSpinLock - Release Spinlock Object to System.
;
; FUNCTIONAL DESCRIPTION.
; This routine is called by large-model C routines to release
; a word of storage used as a spinlock object. The lock is
; released, although this operation is superfluous in this
; particular implementation. Other implementations of this
; package may actually require this routine to deallocate a
; handle.
;
; ENTRY.
; [bp+6,bp+8] - FWA, spinlock to deallocate.
;
; EXIT.
; AX - 0 if success, else nonzero if failure.
;
; USES.
; none.

ASSUME CS:SPINLOCK, DS:NOTHING, ES:NOTHING, SS:NOTHING
DefProc _DeallocateSpinLock
push bp
mov bp, sp
push si
push ds
lds si, [bp+6] ; (DS:SI) = FWA, storage.
DeallocateSpinLock <[si]> ; deallocate the lock.
sub ax, ax ; (AX) = 0, meaning success.
pop ds
pop si
pop bp
EndProc _DeallocateSpinLock

;*** _AcquireSpinLock - Acquire Spinlock for Exclusive Access.
;
; FUNCTIONAL DESCRIPTION.
; This routine is called by large-model C routines to acquire,
; or gain control of, a registered spinlock. This routine works
; by calling the AcquireSpinLock macro, which repeatedly issues
; an XCHG instruction on the lock with a nonzero value until a
; zero value is returned. Because Intel architecture guarantees
; that XCHG will issue a LOCK across the bus, other processors
; cannot interleave their XCHG cycles with ours.
;
; This routine disables interrupts so that ISRs can also use locks.
; If you don't need disabled interrupts, you should remove the CLI
; instruction at the start of this routine, and also remove the STI
; instruction at the end of the _ReleaseSpinLock routine.
;
; A return status code is provided because in some implementations,
; a spinlock's handle may be invalid.
;
; ENTRY.
; [bp+6,bp+8] - FWA, spinlock object.
;
; EXIT.
; AX - 0 if success, else nonzero if failure.
;
; USES.
; none.

ASSUME CS:SPINLOCK, DS:NOTHING, ES:NOTHING, SS:NOTHING
DefProc _AcquireSpinLock
push bp
mov bp, sp
push si
push ds
lds si, [bp+6] ; (DS:SI) = FWA, storage.
cli ; DISABLE INTERRUPTS.
AcquireSpinLock <[si]> ; acquire the lock.
sub ax, ax ; (AX) = 0, meaning success.
pop ds
pop si
pop bp
EndProc _AcquireSpinLock

;*** _ReleaseSpinLock - Release Spinlock to Other Processors.
;
; FUNCTIONAL DESCRIPTION.
; This routine is called by large-model C routines to release
; control of a previously-acquired spinlock. This routine works
; by calling the ReleaseSpinLock macro, which simply stores a
; zero in the lock in a single bus cycle. Because the store
; doesn't cause a read/modify/write cycle that could be interrupted,
; we're safe.
;
; This routine disables interrupts so that ISRs can also use locks.
; If you don't need disabled interrupts, you should remove the STI
; instruction at the end of this routine, and also remove the CLI
; instruction at the beginning of the _AcquireSpinLock routine.
;
; ENTRY.
; [bp+6,bp+8] - FWA, spinlock object.
;
; EXIT.
; AX - 0 if success, else nonzero if failure.
;
; USES.
; none.

ASSUME CS:SPINLOCK, DS:NOTHING, ES:NOTHING, SS:NOTHING
DefProc _ReleaseSpinLock
push bp
mov bp, sp
push si
push ds
lds si, [bp+6] ; (DS:SI) = FWA, storage.
ReleaseSpinLock <[si]> ; release the lock.
sti ; ENABLE INTERRUPTS.
sub ax, ax ; (AX) = 0, meaning success.
pop ds
pop si
pop bp
EndProc _ReleaseSpinLock

SPINLOCK ENDS

END

Figure 2. Spinlock Package for MP-Aware C Programs.