1 files changed, 18 insertions, 118 deletions
diff --git a/src/mongo/util/system_tick_source.cpp b/src/mongo/util/system_tick_source.cpp
index ee5f24d4e83..293b072f079 100644
--- a/src/mongo/util/system_tick_source.cpp
+++ b/src/mongo/util/system_tick_source.cpp
@@ -27,132 +27,32 @@
  *    it in the license file.
  */
 
-#include "mongo/platform/basic.h"
-
 #include "mongo/util/system_tick_source.h"
 
-#include "mongo/config.h"
-
-#include <ctime>
-#include <limits>
-#if defined(MONGO_CONFIG_HAVE_HEADER_UNISTD_H)
-#include <unistd.h>
-#endif
+#include <chrono>  // NOLINT
 #include <memory>
 
-#include "mongo/base/init.h"
-#include "mongo/util/assert_util.h"
 #include "mongo/util/tick_source.h"
-#include "mongo/util/time_support.h"
 
 namespace mongo {
 
-namespace {
-
-const int64_t kMillisPerSecond = 1000;
-const int64_t kMicrosPerSecond = 1000 * kMillisPerSecond;
-const int64_t kNanosPerSecond = 1000 * kMicrosPerSecond;
-
-/**
- * Internally, the timer counts platform-dependent ticks of some sort, and
- * must then convert those ticks to microseconds and their ilk.  This field
- * stores the frequency of the platform-dependent counter.
- *
- * Define ticksPerSecond before init to ensure correct relative sequencing
- * regardless of how it is initialized (static or dynamic).
- */
-TickSource::Tick ticksPerSecond = kMicrosPerSecond;
-
-// "Generic" implementation for _timerNow.
-TickSource::Tick _timerNowGeneric() {
-    return curTimeMicros64();
-}
-
-// Function pointer to timer implementation.
-// Overridden in initTickSource() with better implementation where available.
-TickSource::Tick (*_timerNow)() = &_timerNowGeneric;
-
-#if defined(_WIN32)
-
-/**
- * Windows-specific implementation of the
- * Timer class.  Windows selects the best available timer, in its estimation, for
- * measuring time at high resolution.  This may be the HPET of the TSC on x86 systems,
- * but is promised to be synchronized across processors, barring BIOS errors.
- */
-TickSource::Tick timerNowWindows() {
-    LARGE_INTEGER i;
-    fassert(16161, QueryPerformanceCounter(&i));
-    return i.QuadPart;
-}
-
-void initTickSource() {
-    LARGE_INTEGER x;
-    bool ok = QueryPerformanceFrequency(&x);
-    verify(ok);
-    ticksPerSecond = x.QuadPart;
-    _timerNow = &timerNowWindows;
-}
-
-#elif defined(MONGO_CONFIG_HAVE_POSIX_MONOTONIC_CLOCK)
-
-/**
- * Implementation for timer on systems that support the
- * POSIX clock API and CLOCK_MONOTONIC clock.
- */
-TickSource::Tick timerNowPosixMonotonicClock() {
-    timespec the_time;
-    long long result;
-
-    fassert(16160, !clock_gettime(CLOCK_MONOTONIC, &the_time));
-
-    // Safe for 292 years after the clock epoch, even if we switch to a signed time value.
-    // On Linux, the monotonic clock's epoch is the UNIX epoch.
-    result = static_cast<long long>(the_time.tv_sec);
-    result *= kNanosPerSecond;
-    result += static_cast<long long>(the_time.tv_nsec);
-    return result;
-}
-
-void initTickSource() {
-    // If the monotonic clock is not available at runtime (sysconf() returns 0 or -1),
-    // do not override the generic implementation or modify ticksPerSecond.
-    if (sysconf(_SC_MONOTONIC_CLOCK) <= 0) {
-        return;
-    }
-
-    ticksPerSecond = kNanosPerSecond;
-    _timerNow = &timerNowPosixMonotonicClock;
-
-    // Make sure that the current time relative to the (unspecified) epoch isn't already too
-    // big to represent as a 64-bit count of nanoseconds.
-    long long maxSecs = std::numeric_limits<long long>::max() / kNanosPerSecond;
-    timespec the_time;
-    fassert(16162, !clock_gettime(CLOCK_MONOTONIC, &the_time));
-    fassert(16163, static_cast<long long>(the_time.tv_sec) < maxSecs);
-}
-#else
-void initTickSource() {}
-#endif
-
-}  // unnamed namespace
-
-MONGO_INITIALIZER(SystemTickSourceInit)(InitializerContext* context) {
-    initTickSource();
-    SystemTickSource::get();
-}
-
-TickSource::Tick SystemTickSource::getTicks() {
-    return _timerNow();
-}
-
-TickSource::Tick SystemTickSource::getTicksPerSecond() {
-    return ticksPerSecond;
-}
-
-SystemTickSource* SystemTickSource::get() {
-    static const auto globalSystemTickSource = std::make_unique<SystemTickSource>();
-    return globalSystemTickSource.get();
+std::unique_ptr<TickSource> makeSystemTickSource() {
+    class Steady : public TickSource {
+        using C = std::chrono::steady_clock;  // NOLINT
+        Tick getTicksPerSecond() override {
+            static_assert(C::period::num == 1, "Fractional frequency disallowed");
+            return C::period::den;
+        }
+        Tick getTicks() override {
+            return C::now().time_since_epoch().count();
+        }
+    };
+    return std::make_unique<Steady>();
+}
+
+TickSource* globalSystemTickSource() {
+    static const auto p = makeSystemTickSource().release();
+    return p;
 }
 
 }  // namespace mongo