spinlock tryacquire

5b20acce · Silas Boyd-Wickizer · 525f0d7d · 5b20acce · 5b20acce
--- a/kernel.h
+++ b/kernel.h
@@ -247,6 +247,7 @@ void            sampconf(void);

 // spinlock.c
 void            acquire(struct spinlock*);
+int             tryacquire(struct spinlock*);
 void            getcallerpcs(void*, uptr*);
 int             holding(struct spinlock*);
 void            initlock(struct spinlock*, char*);

--- a/spinlock.c
+++ b/spinlock.c
@@ -18,6 +18,33 @@ initlock(struct spinlock *lk, char *name)
  lk->locked = 0;
 }

+int
+tryacquire(struct spinlock *lk)
+{
+  pushcli(); // disable interrupts to avoid deadlock.
+
+#if SPINLOCK_DEBUG
+  if(holding(lk)) {
+    cprintf("%lx\n", __builtin_return_address(0));
+    panic("acquire");
+  }
+#endif
+
+  mtlock(lk);
+  if (xchg32(&lk->locked, 1) != 0) {
+      popcli();
+      return 0;
+  }
+  mtacquired(lk);
+
+#if SPINLOCK_DEBUG
+  // Record info about lock acquisition for debugging.
+  lk->cpu = mycpu();
+  getcallerpcs(&lk, lk->pcs);
+#endif
+  return 1;
+}
+
 // Acquire the lock.
 // Loops (spins) until the lock is acquired.
 // Holding a lock for a long time may cause