[host]: add EnableBootTimeCache function

README.md

@@ -109,6 +109,17 @@ As of v3.23.6, it is now possible to pass a path location using `context`: impor
 
 First priority is given to the value set in `context`, then the value from the environment variable, and finally the default location.
 
+### Caching
+
+As of v3.24.1, it is now possible to cached some values. These values default to false, not cached. 
+
+Be very careful that enabling the cache may cause inconsistencies. For example, if you enable caching of boottime on Linux, be aware that unintended values may be returned if [the boottime is changed by NTP after booted](https://github.com/shirou/gopsutil/issues/1070#issuecomment-842512782).
+
+- `host`
+  - EnableBootTimeCache
+- `process`
+  - EnableBootTimeCache
+
 ## Documentation
 
 See https://pkg.go.dev/github.com/shirou/gopsutil/v3 or https://godocs.io/github.com/shirou/gopsutil/v3

host/host.go

@@ -62,6 +62,13 @@ func (t TemperatureStat) String() string {
 	return string(s)
 }
 
+var enableBootTimeCache bool
+
+// EnableBootTimeCache change cache behavior of BootTime. If true, cache BootTime value. Default is false.
+func EnableBootTimeCache(enable bool) {
+	enableBootTimeCache = enable
+}
+
 func Info() (*InfoStat, error) {
 	return InfoWithContext(context.Background())
 }

host/host_bsd.go

@@ -14,16 +14,20 @@ import (
 var cachedBootTime uint64
 
 func BootTimeWithContext(ctx context.Context) (uint64, error) {
-	t := atomic.LoadUint64(&cachedBootTime)
-	if t != 0 {
-		return t, nil
+	if enableBootTimeCache {
+		t := atomic.LoadUint64(&cachedBootTime)
+		if t != 0 {
+			return t, nil
+		}
 	}
 	tv, err := unix.SysctlTimeval("kern.boottime")
 	if err != nil {
 		return 0, err
 	}
 
-	atomic.StoreUint64(&cachedBootTime, uint64(tv.Sec))
+	if enableBootTimeCache {
+		atomic.StoreUint64(&cachedBootTime, uint64(tv.Sec))
+	}
 
 	return uint64(tv.Sec), nil
 }

host/host_linux.go

@@ -71,7 +71,7 @@ func numProcs(ctx context.Context) (uint64, error) {
 }
 
 func BootTimeWithContext(ctx context.Context) (uint64, error) {
-	return common.BootTimeWithContext(ctx)
+	return common.BootTimeWithContext(ctx, enableBootTimeCache)
 }
 
 func UptimeWithContext(ctx context.Context) (uint64, error) {

host/host_test.go

@@ -195,3 +195,17 @@ func TestPlatformInformation(t *testing.T) {
 
 	t.Logf("PlatformInformation(): %v, %v, %v", platform, family, version)
 }
+
+func BenchmarkBootTimeWithCache(b *testing.B) {
+	EnableBootTimeCache(true)
+	for i := 0; i < b.N; i++ {
+		BootTime()
+	}
+}
+
+func BenchmarkBootTimeWithoutCache(b *testing.B) {
+	EnableBootTimeCache(false)
+	for i := 0; i < b.N; i++ {
+		BootTime()
+	}
+}

host/host_windows.go

@@ -127,16 +127,20 @@ func uptimeMillis() (uint64, error) {
 var cachedBootTime uint64
 
 func BootTimeWithContext(ctx context.Context) (uint64, error) {
-	t := atomic.LoadUint64(&cachedBootTime)
-	if t != 0 {
-		return t, nil
+	if enableBootTimeCache {
+		t := atomic.LoadUint64(&cachedBootTime)
+		if t != 0 {
+			return t, nil
+		}
 	}
 	up, err := uptimeMillis()
 	if err != nil {
 		return 0, err
 	}
-	t = uint64((time.Duration(timeSinceMillis(up)) * time.Millisecond).Seconds())
-	atomic.StoreUint64(&cachedBootTime, t)
+	t := uint64((time.Duration(timeSinceMillis(up)) * time.Millisecond).Seconds())
+	if enableBootTimeCache {
+		atomic.StoreUint64(&cachedBootTime, t)
+	}
 	return t, nil
 }
 

internal/common/common_linux.go

@@ -12,10 +12,14 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 )
 
+// cachedBootTime must be accessed via atomic.Load/StoreUint64
+var cachedBootTime uint64
+
 func DoSysctrl(mib string) ([]string, error) {
 	cmd := exec.Command("sysctl", "-n", mib)
 	cmd.Env = getSysctrlEnv(os.Environ())
@@ -56,7 +60,14 @@ func NumProcsWithContext(ctx context.Context) (uint64, error) {
 	return cnt, nil
 }
 
-func BootTimeWithContext(ctx context.Context) (uint64, error) {
+func BootTimeWithContext(ctx context.Context, enableCache bool) (uint64, error) {
+	if enableCache {
+		t := atomic.LoadUint64(&cachedBootTime)
+		if t != 0 {
+			return t, nil
+		}
+	}
+
 	system, role, err := VirtualizationWithContext(ctx)
 	if err != nil {
 		return 0, err
@@ -72,7 +83,13 @@ func BootTimeWithContext(ctx context.Context) (uint64, error) {
 	}
 
 	if useStatFile {
-		return readBootTimeStat(ctx)
+		t, err := readBootTimeStat(ctx)
+		if err != nil {
+			return 0, err
+		}
+		if enableCache {
+			atomic.StoreUint64(&cachedBootTime, t)
+		}
 	}
 
 	filename := HostProcWithContext(ctx, "uptime")
@@ -90,6 +107,11 @@ func BootTimeWithContext(ctx context.Context) (uint64, error) {
 	}
 	currentTime := float64(time.Now().UnixNano()) / float64(time.Second)
 	t := currentTime - b
+
+	if enableCache {
+		atomic.StoreUint64(&cachedBootTime, uint64(t))
+	}
+
 	return uint64(t), nil
 }
 

process/process.go

@@ -171,6 +171,13 @@ func (p NumCtxSwitchesStat) String() string {
 	return string(s)
 }
 
+var enableBootTimeCache bool
+
+// EnableBootTimeCache change cache behavior of BootTime. If true, cache BootTime value. Default is false.
+func EnableBootTimeCache(enable bool) {
+	enableBootTimeCache = enable
+}
+
 // Pids returns a slice of process ID list which are running now.
 func Pids() ([]int32, error) {
 	return PidsWithContext(context.Background())

process/process_linux.go

@@ -1071,7 +1071,7 @@ func (p *Process) fillFromTIDStatWithContext(ctx context.Context, tid int32) (ui
 		Iowait: iotime / float64(clockTicks),
 	}
 
-	bootTime, _ := common.BootTimeWithContext(ctx)
+	bootTime, _ := common.BootTimeWithContext(ctx, enableBootTimeCache)
 	t, err := strconv.ParseUint(fields[22], 10, 64)
 	if err != nil {
 		return 0, 0, nil, 0, 0, 0, nil, err