Use a monotonic clock in the implementation of Timer.

runtime/bin/utils_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include <errno.h>  // NOLINT
 #include <netdb.h>  // NOLINT
 #include <sys/time.h>  // NOLINT
@@ skipping 51 matching lines @@
 char* StringUtils::Utf8ToConsoleString(
     char* utf8, intptr_t len, intptr_t* result_len) {
   UNIMPLEMENTED();
   return NULL;
 }
 
 bool ShellUtils::GetUtf8Argv(int argc, char** argv) {
   return false;
 }
 
-int64_t TimerUtils::GetCurrentTimeMilliseconds() {
-  return GetCurrentTimeMicros() / 1000;
+int64_t TimerUtils::GetCurrentMonotonicMillis() {
+  return GetCurrentMonotonicMicros() / 1000;
 }
 
-int64_t TimerUtils::GetCurrentTimeMicros() {
-  struct timeval tv;
-  if (gettimeofday(&tv, NULL) < 0) {
+int64_t TimerUtils::GetCurrentMonotonicMicros() {
+  struct timespec ts;
+  if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0) {
     UNREACHABLE();
     return 0;
   }
-  return (static_cast<int64_t>(tv.tv_sec) * 1000000) + tv.tv_usec;
+  // Convert to microseconds.
+  int64_t result = ts.tv_sec;
+  result *= kMicrosecondsPerSecond;
+  result += (ts.tv_nsec / kNanosecondsPerMicrosecond);
+  return result;
 }
 
 void TimerUtils::Sleep(int64_t millis) {
   struct timespec req;  // requested.
   struct timespec rem;  // remainder.
   int64_t micros = millis * kMicrosecondsPerMillisecond;
   int64_t seconds = micros / kMicrosecondsPerSecond;
   micros = micros - seconds * kMicrosecondsPerSecond;
   int64_t nanos = micros * kNanosecondsPerMicrosecond;
   req.tv_sec = seconds;
   req.tv_nsec = nanos;
   while (true) {
     int r = nanosleep(&req, &rem);
     if (r == 0) {
       break;
     }
     // We should only ever see an interrupt error.
     ASSERT(errno == EINTR);
     // Copy remainder into requested and repeat.
     req = rem;
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)