a

kern/qlock.c

@@ -0,0 +1,94 @@
+#include "u.h"
+#include "lib.h"
+#include "dat.h"
+#include "fns.h"
+
+static void
+queue(Proc **first, Proc **last)
+{
+	Proc *t;
+
+	t = *last;
+	if(t == 0)
+		*first = up;
+	else
+		t->qnext = up;
+	*last = up;
+	up->qnext = 0;
+}
+
+static Proc*
+dequeue(Proc **first, Proc **last)
+{
+	Proc *t;
+
+	t = *first;
+	if(t == 0)
+		return 0;
+	*first = t->qnext;
+	if(*first == 0)
+		*last = 0;
+	return t;
+}
+
+void
+qlock(QLock *q)
+{
+	lock(&q->lk);
+
+	if(q->hold == 0) {
+		q->hold = up;
+		unlock(&q->lk);
+		return;
+	}
+
+	/*
+	 * Can't assert this because of RWLock
+	assert(q->hold != up);
+	 */		
+
+	queue((Proc**)&q->first, (Proc**)&q->last);
+	unlock(&q->lk);
+	procsleep();
+}
+
+int
+canqlock(QLock *q)
+{
+	lock(&q->lk);
+	if(q->hold == 0) {
+		q->hold = up;
+		unlock(&q->lk);
+		return 1;
+	}
+	unlock(&q->lk);
+	return 0;
+}
+
+void
+qunlock(QLock *q)
+{
+	Proc *p;
+
+	lock(&q->lk);
+	/* 
+	 * Can't assert this because of RWlock
+	assert(q->hold == CT);
+	 */
+	p = dequeue((Proc**)&q->first, (Proc**)&q->last);
+	if(p) {
+		q->hold = p;
+		unlock(&q->lk);
+		procwakeup(p);
+	} else {
+		q->hold = 0;
+		unlock(&q->lk);
+	}
+}
+
+int
+holdqlock(QLock *q)
+{
+	return q->hold == up;
+}
+