Opt spin lock (alibaba#1126)

Author: EricHuangqx

thread/thread.h

@@ -214,13 +214,22 @@ namespace photon
 #endif
     }
 
+    inline void spin_wait_n(uint32_t n) {
+        for (uint32_t i = 0; i < n; ++i) {
+            spin_wait();
+        }
+    }
+
     class spinlock {
     public:
         int lock() {
+            uint32_t delay = 1;
+            constexpr uint32_t max_delay = 1024;
             while (unlikely(xchg())) {
-                while (likely(load())) {
-                    spin_wait();
-                }
+                do {
+                    spin_wait_n(delay);
+                    if (delay < max_delay) delay <<= 1;
+                } while (likely(load()));
             }
             return 0;
         }