A qlock implementation.

c303d067 · Silas Boyd-Wickizer · 64137fa7 · c303d067 · c303d067
--- a/amd64.h
+++ b/amd64.h
@@ -39,6 +39,17 @@ xchg32(volatile u32 *addr, u32 newval)
 }
 static inline u64
+xchg(u64 *ptr, u64 val)
+{
+  __asm volatile(
+    "lock; xchgq %0, %1\n\t"
+    : "+m" (*ptr), "+r" (val)
+    :
+    : "memory", "cc");
+  return val;
+}
+static inline u64
 readrflags(void)
 {
  u64 rflags;
@@ -65,6 +76,18 @@ nop_pause(void)
 }
 static inline void
+rep_nop(void)
+{
+  __asm volatile("rep; nop" ::: "memory");
+}
+static inline void
+barrier(void)
+{
+  __asm volatile("" ::: "memory");
+}
+static inline void
 lidt(void *p)
 {
  __asm volatile("lidt (%0)" : : "r" (p) : "memory");

--- a/qlock.h
+++ b/qlock.h
+struct qnode {
+  volatile void *next;
+  volatile char locked;
+  __padout__;
+};
+typedef struct {
+  struct qnode *v __mpalign__;
+} qlock_t;
+static inline void
+ql_init(qlock_t *l)
+{
+        l->v = NULL;
+}
+static inline void
+ql_lock(qlock_t *l, volatile struct qnode *mynode)
+{
+  struct qnode *predecessor;
+  mynode->next = NULL;
+  predecessor = (struct qnode *)xchg((u64 *)&l->v, (u64)mynode);
+  if (predecessor) {
+    mynode->locked = 1;
+    barrier();
+    predecessor->next = mynode;
+    while (mynode->locked)
+      rep_nop();
+  }
+}
+static inline int
+ql_trylock(qlock_t *l, volatile struct qnode *mynode)
+{
+  mynode->next = NULL;
+  return cmpswap((long *)&l->v, 0, (long)mynode);
+}
+static inline void
+ql_unlock(qlock_t *l, volatile struct qnode *mynode)
+{
+  if (!mynode->next) {
+    if (cmpswap((long *)&l->v, (long)mynode, 0))
+      return;
+    while (!mynode->next)
+      rep_nop();
+  }
+  ((struct qnode *)mynode->next)->locked = 0;
+}