Add bvar/scoped_timer.h to time scopes with bvar more conveniently

Change-Id: I1bfb3347751e6492991b70450cc84023e902f908

bvar/bvar.h

@@ -12,5 +12,6 @@
 #include "bvar/passive_status.h"
 #include "bvar/latency_recorder.h"
 #include "bvar/gflag.h"
+#include "bvar/scoped_timer.h"
 
 #endif  //BVAR_BVAR_H

bvar/scoped_timer.h

+// Baidu RPC - A framework to host and access services throughout Baidu.
+// Copyright (c) 2017 Baidu.com, Inc. All Rights Reserved
+
+// Author: The baidu-rpc authors (pbrpc@baidu.com)
+// Date: Fri Jul 14 11:29:21 CST 2017
+
+#ifndef  BVAR_SCOPED_TIMER_H
+#define  BVAR_SCOPED_TIMER_H
+
+#include "base/time.h"
+
+// Accumulate microseconds spent by scopes into bvar, useful for debugging.
+// Example:
+//   bvar::Adder<int64_t> g_function1_spent;
+//   ...
+//   void function1() {
+//     // time cost by function1() will be sent to g_spent_time when
+//     // the function returns.
+//     bvar::ScopedTimer tm(g_function1_spent);
+//     ...
+//   }
+// To check how many microseconds the function spend in last second, you
+// can wrap the bvar within PerSecond and make it viewable from /vars
+//   bvar::PerSecond<bvar::Adder<int64_t> > g_function1_spent_second(
+//     "function1_spent_second", &g_function1_spent);
+namespace bvar{
+template <typename T>
+class ScopedTimer {
+public:
+    explicit ScopedTimer(T& bvar)
+        : _start_time(base::cpuwide_time_us()), _bvar(&bvar) {}
+
+    ~ScopedTimer() {
+        *_bvar << (base::cpuwide_time_us() - _start_time);
+    }
+
+    void reset() { _start_time = base::cpuwide_time_us(); }
+
+private:
+    DISALLOW_COPY_AND_ASSIGN(ScopedTimer);
+    const int64_t _start_time;
+    T* _bvar;
+};
+} // namespace bvar
+
+#endif  //BVAR_SCOPED_TIMER_H