你看看这段代码就清楚了。
; Intel syntax
lock: ; The lock variable. 1 = locked, 0 = unlocked.
dd 0
spin_lock:
mov eax, 1 ; Set the EAX register to 1.
xchg eax, [lock] ; Atomically swap the EAX register with
; the lock variable.
; This will always store 1 to the lock, leaving
; previous value in the EAX register.
test eax, eax ; Test EAX with itself. Among other things,
this will
; set the processor's Zero Flag if EAX is 0.
; If EAX is 0, then the lock was unlocked and
; we just locked it.
; Otherwise, EAX is 1 and we didn't acquire the
lock.
jnz spin_lock ; Jump back to the XCHG instruction if the Zero
Flag is
; not set; the lock was previously locked, and
so
; we need to spin until it becomes unlocked.
ret ; The lock has been acquired, return to the
calling
; function.
spin_unlock:
mov eax, 0 ; Set the EAX register to 0.
xchg eax, [lock] ; Atomically swap the EAX register with
; the lock variable.
ret ; The lock has been released.
