github.com/aristanetworks/goarista@v0.0.0-20240514173732-cca2755bbd44/monotime/nanotime.go (about)

     1  // Copyright (c) 2016 Arista Networks, Inc.
     2  // Use of this source code is governed by the Apache License 2.0
     3  // that can be found in the COPYING file.
     4  
     5  // Package monotime provides a fast monotonic clock source.
     6  package monotime
     7  
     8  import (
     9  	"time"
    10  	_ "unsafe" // required to use //go:linkname
    11  )
    12  
    13  //go:noescape
    14  //go:linkname nanotime runtime.nanotime
    15  func nanotime() int64
    16  
    17  // Now returns the current time in nanoseconds from a monotonic clock.
    18  // The time returned is based on some arbitrary platform-specific point in the
    19  // past.  The time returned is guaranteed to increase monotonically at a
    20  // constant rate, unlike time.Now() from the Go standard library, which may
    21  // slow down, speed up, jump forward or backward, due to NTP activity or leap
    22  // seconds.
    23  func Now() uint64 {
    24  	return uint64(nanotime())
    25  }
    26  
    27  // Since returns the amount of time that has elapsed since t. t should be
    28  // the result of a call to Now() on the same machine.
    29  func Since(t uint64) time.Duration {
    30  	return time.Duration(Now() - t)
    31  }