Check wq length before trying to steal

7c717316 · Silas Boyd-Wickizer · 92624e13 · 7c717316
--- a/lib/wqlib.cc
+++ b/lib/wqlib.cc
@@ -41,10 +41,15 @@ void
 wq::dump(void)
 {
  int i;
-  for (i = 0; i < NCPU; i++)
+  for (i = 0; i < NCPU; i++) {
    xprintf("push %lu full %lu pop %lu steal %lu\n",
            stat_[i].push, stat_[i].full,
            stat_[i].pop, stat_[i].steal);
+    stat_[i].push = 0;
+    stat_[i].full = 0;
+    stat_[i].pop = 0;
+    stat_[i].steal = 0;
+  }
 }

 inline void
@@ -120,12 +125,16 @@ wq::steal(int c)
  work *w;
  int i;

+  i = q->tail;
+  if ((i - q->head) == 0)
+    return nullptr;
+
  if (wqlock_tryacquire(&q->lock) == 0)
-    return 0;
+    return nullptr;
  i = q->tail;
  if ((i - q->head) == 0) {
    wqlock_release(&q->lock);
-    return 0;
+    return nullptr;
  }
  i = i & (NSLOTS-1);
  w = q->w[i];