use the linux monotonic clock instead of gettimeofday

luprex/core/cpp/driver-linux.cpp

@@ -117,6 +117,32 @@ SOCKET listen_on_port(int port, std::string &err) {
     return sock;
 }
 
+class MonoClock {
+private:
+    struct timespec base_;
+public:
+    MonoClock() {
+        int status = clock_gettime(CLOCK_MONOTONIC, &base_);
+        assert(status == 0);
+    }
+    double get() {
+        struct timespec t;
+        int status = clock_gettime(CLOCK_MONOTONIC, &t);
+        assert(status == 0);
+        double tv_sec = t.tv_sec - base_.tv_sec;
+        double tv_nsec = t.tv_nsec - base_.tv_nsec;
+        return tv_sec + (tv_nsec * 1.0E-9);
+    }
+};
+
+static MonoClock monoclock;
+
+namespace util {
+    double profiling_clock() {
+        return monoclock.get();
+    }
+}
+
 class Driver {
 public:
     enum ChanState {
@@ -135,15 +161,6 @@ public:
     bool short_sleep_;
     std::map<int, SOCKET> listen_sockets_;
     std::unique_ptr<char[]> chbuf;
-    int64_t basetime_;
-
-    int64_t get_now() {
-        struct timeval tv;
-        gettimeofday(&tv, nullptr);
-        int64_t tv_sec = tv.tv_sec;
-        int64_t tv_usec = tv.tv_usec;
-        return tv_sec * 1000000 + tv_usec;
-    }
 
     void init(DrivenEngine *de) {
         driven_ = de;
@@ -228,8 +245,7 @@ public:
     }
 
     void handle_clock() {
-        int64_t now = get_now() - basetime_;
-        driven_->drv_set_clock(double(now) / 1000000.0);
+        driven_->drv_set_clock(monoclock.get());
     }
 
     void close_channel(int chid, const std::string err) {
@@ -340,7 +356,6 @@ public:
         enableRawMode();
         init(de);
         DrivenEngine::set(de);
-        basetime_ = get_now();
         driven_->drv_set_lua_source(util::read_lua_source("lua"));
         driven_->drv_invoke_event_init(argc, argv);
         handle_listen_ports();