Fixing issue #583. Using low resolution timer for clock::now_ms

src/clock.cpp

@@ -22,6 +22,7 @@
 #include "likely.hpp"
 #include "config.hpp"
 #include "err.hpp"
+#include "mutex.hpp"
 
 #include <stddef.h>
 
@@ -41,9 +42,47 @@
 #include <time.h>
 #endif
 
+typedef ULONGLONG (*f_compatible_get_tick_count64)();
+
+static zmq::mutex_t compatible_get_tick_count64_mutex;
+
+ULONGLONG compatible_get_tick_count64()
+{
+  compatible_get_tick_count64_mutex.lock();
+  static DWORD s_wrap = 0;
+  static DWORD s_last_tick = 0;
+  const DWORD current_tick = ::GetTickCount();
+  if (current_tick < s_last_tick)
+    ++s_wrap;
+
+  s_last_tick = current_tick;
+  const ULONGLONG result = (static_cast<ULONGLONG>(s_wrap) << 32) + static_cast<ULONGLONG>(current_tick);
+  compatible_get_tick_count64_mutex.unlock();
+  return result;
+}
+
+f_compatible_get_tick_count64 init_compatible_get_tick_count64()
+{
+  f_compatible_get_tick_count64 func = NULL;
+  HMODULE module = ::LoadLibraryA("Kernel32.dll");
+  if (module != NULL)
+    func = reinterpret_cast<f_compatible_get_tick_count64>(::GetProcAddress(module, "GetTickCount64"));
+
+  if (func == NULL)
+    func = compatible_get_tick_count64;
+
+  return func;
+}
+
+static f_compatible_get_tick_count64 my_get_tick_count64 = init_compatible_get_tick_count64();
+
 zmq::clock_t::clock_t () :
     last_tsc (rdtsc ()),
+#ifdef ZMQ_HAVE_WINDOWS
+    last_time (static_cast<uint64_t>((*my_get_tick_count64)()))
+#else
     last_time (now_us () / 1000)
+#endif
 {
 }
 
@@ -65,7 +104,7 @@ uint64_t zmq::clock_t::now_us ()
 
     //  Convert the tick number into the number of seconds
     //  since the system was started.
-    double ticks_div = ticksPerSecond.QuadPart / 1000000.0;     
+    double ticks_div = ticksPerSecond.QuadPart / 1000000.0;
     return (uint64_t) (tick.QuadPart / ticks_div);
 
 #elif defined HAVE_CLOCK_GETTIME && defined CLOCK_MONOTONIC
@@ -74,7 +113,7 @@ uint64_t zmq::clock_t::now_us ()
     struct timespec tv;
     int rc = clock_gettime (CLOCK_MONOTONIC, &tv);
 		// Fix case where system has clock_gettime but CLOCK_MONOTONIC is not supported.
-		// This should be a configuration check, but I looked into it and writing an 
+		// This should be a configuration check, but I looked into it and writing an
 		// AC_FUNC_CLOCK_MONOTONIC seems beyond my powers.
 		if( rc != 0) {
 			//  Use POSIX gettimeofday function to get precise time.
@@ -106,7 +145,18 @@ uint64_t zmq::clock_t::now_ms ()
 
     //  If TSC is not supported, get precise time and chop off the microseconds.
     if (!tsc)
+    {
+#ifdef ZMQ_HAVE_WINDOWS
+        // Under Windows, now_us is not so reliable since QueryPerformanceCounter
+        // does not guarantee that it will use a hardware that offers a monotonic timer.
+        // So, lets use GetTickCount when GetTickCount64 is not available with an workaround
+        // to its 32 bit limitation.
+        static_assert(sizeof(uint64_t) >= sizeof(ULONGLONG), "Loosing timer information");
+        return static_cast<uint64_t>((*my_get_tick_count64)());
+#else
         return now_us () / 1000;
+#endif
+    }
 
     //  If TSC haven't jumped back (in case of migration to a different
     //  CPU core) and if not too much time elapsed since last measurement,
@@ -115,7 +165,11 @@ uint64_t zmq::clock_t::now_ms ()
         return last_time;
 
     last_tsc = tsc;
+#ifdef ZMQ_HAVE_WINDOWS
+    last_time = static_cast<uint64_t>((*my_get_tick_count64)());
+#else
     last_time = now_us () / 1000;
+#endif
     return last_time;
 }