* fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
 * interacting with this class directly.
 *
 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
 *
 * @author Kevin Bourrillion
 * @since 10.0 (<a href="https://github.com/google/guava/wiki/Compatibility">mostly
 *     source-compatible</a> since 9.0)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault

 * fixed but arbitrary point in time. Note that most users should use {@link Stopwatch} instead of
 * interacting with this class directly.
 *
 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
 *
 * @author Kevin Bourrillion
 * @since 10.0 (<a href="https://github.com/google/guava/wiki/Compatibility">mostly
 *     source-compatible</a> since 9.0)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault

// Distribution of checkpoint write durations.
auto* checkpoint_write_durations = monitoring::Sampler<1>::New(
    {
        "/tensorflow/core/checkpoint/write/write_durations",  // Metric name.
        "Distribution of the wall time duration in microseconds of the "
        "checkpoint write operation.",  // Metric description.
        "api_label"                     // Cell label.
    },

    }

    /**
     * Measures elapsed time.
     *
     * Timers use System.nanoTime() to measure elapsed time,
     * and are therefore not synchronized with {@link #clock()} or the system wall clock.
     *
     * System.nanoTime() does not consider time elapsed while the system is in hibernation.
     * Therefore, timers effectively measure the elapsed time, of which the system was awake.
     */

        when:
        setNanos(delta)

        then:
        clock.currentTime == START_MILLIS + Math.max(0, delta)

        where:
        delta << [0, 100, -100]
    }

    def "resyncs with system wall clock"() {
        when:
        setNanos(10)

        then:
        clock.currentTime == time(10)

        when:
        setNanos(15)

        then:
        clock.currentTime == time(15)

    }

    /**
     * The elapsed wall clock time of executing the actual work, i.e. the time it took to execute the
     * {@link UnitOfWork#execute(UnitOfWork.ExecutionRequest)} method.
     *
     * The execution time refers to when and where the work was executed: if a previous result was reused,
     * then this method will return the time it took to produce the previous result.
     *

 *
 * <p>In contrast, <i>wall time</i> is a reading of "now" as given by a method like
 * {@link System#currentTimeMillis()}, best represented as an {@link java.time.Instant}. Such values
 * <i>can</i> be subtracted to obtain a {@code Duration} (such as by {@code Duration.between}), but
 * doing so does <i>not</i> give a reliable measurement of elapsed time, because wall time readings

 *
 * <p>In contrast, <i>wall time</i> is a reading of "now" as given by a method like
 * {@link System#currentTimeMillis()}, best represented as an {@link java.time.Instant}. Such values
 * <i>can</i> be subtracted to obtain a {@code Duration} (such as by {@code Duration.between}), but
 * doing so does <i>not</i> give a reliable measurement of elapsed time, because wall time readings

        given:
        app.writeSources(file('src/main'))

        and:
        buildFile << """
model {
    components {
        main(NativeExecutableSpec) {
            binaries.all {
                cppCompiler.args "-Wall", "-Werror"
            }
        }
    }
}
         """

        expect:
        succeeds "mainExecutable"

#include "tensorflow/core/platform/types.h"

namespace tensorflow {
namespace tfcompile {
namespace benchmark {

// Returns current wall time in micros.
//
// TODO(b/33546473): Refactor tensorflow::Env::NowMicros() so that we can re-use
// the implementation without pulling in all of the Env dependencies.
static uint64 NowMicros() {
  struct timeval tv;
  gettimeofday(&tv, nullptr);