calculate cpu percentage compared to last call if 0 interval is given

cpu/cpu.go

@@ -5,6 +5,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 )
 
 type TimesStat struct {
@@ -37,8 +38,21 @@ type InfoStat struct {
 	Flags      []string `json:"flags"`
 }
 
-var lastCPUTimes []TimesStat
-var lastPerCPUTimes []TimesStat
+//CPUPercent
+type cpuPercent struct {
+	sync.Mutex
+	lastCPUTimes    []TimesStat
+	lastPerCPUTimes []TimesStat
+}
+
+var lastCPUPercent cpuPercent
+
+func init() {
+	lastCPUPercent.Lock()
+	lastCPUPercent.lastCPUTimes, _ = Times(false)
+	lastCPUPercent.lastPerCPUTimes, _ = Times(true)
+	lastCPUPercent.Unlock()
+}
 
 func Counts(logical bool) (int, error) {
 	return runtime.NumCPU(), nil

cpu/cpu_test.go

@@ -94,6 +94,40 @@ func testCPUPercent(t *testing.T, percpu bool) {
 	}
 }
 
+func testCPUPercentLastUsed(t *testing.T, percpu bool) {
+
+	numcpu := runtime.NumCPU()
+	testCount := 10
+
+	if runtime.GOOS != "windows" {
+		testCount = 2
+		v, err := Percent(time.Millisecond, percpu)
+		if err != nil {
+			t.Errorf("error %v", err)
+		}
+		// Skip CircleCI which CPU num is different
+		if os.Getenv("CIRCLECI") != "true" {
+			if (percpu && len(v) != numcpu) || (!percpu && len(v) != 1) {
+				t.Fatalf("wrong number of entries from CPUPercent: %v", v)
+			}
+		}
+	}
+	for i := 0; i < testCount; i++ {
+		v, err := Percent(0, percpu)
+		if err != nil {
+			t.Errorf("error %v", err)
+		}
+		time.Sleep(1 * time.Millisecond)
+		for _, percent := range v {
+			// Check for slightly greater then 100% to account for any rounding issues.
+			if percent < 0.0 || percent > 100.0001*float64(numcpu) {
+				t.Fatalf("CPUPercent value is invalid: %f", percent)
+			}
+		}
+	}
+
+}
+
 func TestCPUPercent(t *testing.T) {
 	testCPUPercent(t, false)
 }
@@ -101,3 +135,11 @@ func TestCPUPercent(t *testing.T) {
 func TestCPUPercentPerCpu(t *testing.T) {
 	testCPUPercent(t, true)
 }
+
+func TestCPUPercentIntervalZero(t *testing.T) {
+	testCPUPercentLastUsed(t, false)
+}
+
+func TestCPUPercentIntervalZeroPerCPU(t *testing.T) {
+	testCPUPercentLastUsed(t, true)
+}

cpu/cpu_unix.go

@@ -7,24 +7,46 @@ import (
 	"time"
 )
 
-func Percent(interval time.Duration, percpu bool) ([]float64, error) {
-	getAllBusy := func(t TimesStat) (float64, float64) {
-		busy := t.User + t.System + t.Nice + t.Iowait + t.Irq +
-			t.Softirq + t.Steal + t.Guest + t.GuestNice + t.Stolen
-		return busy + t.Idle, busy
+func getAllBusy(t TimesStat) (float64, float64) {
+	busy := t.User + t.System + t.Nice + t.Iowait + t.Irq +
+		t.Softirq + t.Steal + t.Guest + t.GuestNice + t.Stolen
+	return busy + t.Idle, busy
+}
+
+func calculateBusy(t1, t2 TimesStat) float64 {
+	t1All, t1Busy := getAllBusy(t1)
+	t2All, t2Busy := getAllBusy(t2)
+
+	if t2Busy <= t1Busy {
+		return 0
+	}
+	if t2All <= t1All {
+		return 1
+	}
+	return (t2Busy - t1Busy) / (t2All - t1All) * 100
+}
+
+func calcualteALLBusy(t1, t2 []TimesStat) ([]float64, error) {
+	// Make sure the CPU measurements have the same length.
+	if len(t1) != len(t2) {
+		return nil, fmt.Errorf(
+			"received two CPU counts: %d != %d",
+			len(t1), len(t2),
+		)
 	}
 
-	calculate := func(t1, t2 TimesStat) float64 {
-		t1All, t1Busy := getAllBusy(t1)
-		t2All, t2Busy := getAllBusy(t2)
+	ret := make([]float64, len(t1))
+	for i, t := range t2 {
+		ret[i] = calculateBusy(t1[i], t)
+	}
+	return ret, nil
+}
 
-		if t2Busy <= t1Busy {
-			return 0
-		}
-		if t2All <= t1All {
-			return 1
-		}
-		return (t2Busy - t1Busy) / (t2All - t1All) * 100
+//Percent calculates the percentage of cpu used either per CPU or combined.
+//If an interval of 0 is given it will compare the current cpu times against the last call.
+func Percent(interval time.Duration, percpu bool) ([]float64, error) {
+	if interval <= 0 {
+		return percentUsedFromLastCall(percpu)
 	}
 
 	// Get CPU usage at the start of the interval.
@@ -33,9 +55,7 @@ func Percent(interval time.Duration, percpu bool) ([]float64, error) {
 		return nil, err
 	}
 
-	if interval > 0 {
-		time.Sleep(interval)
-	}
+	time.Sleep(interval)
 
 	// And at the end of the interval.
 	cpuTimes2, err := Times(percpu)
@@ -43,17 +63,28 @@ func Percent(interval time.Duration, percpu bool) ([]float64, error) {
 		return nil, err
 	}
 
-	// Make sure the CPU measurements have the same length.
-	if len(cpuTimes1) != len(cpuTimes2) {
-		return nil, fmt.Errorf(
-			"received two CPU counts: %d != %d",
-			len(cpuTimes1), len(cpuTimes2),
-		)
+	return calcualteALLBusy(cpuTimes1, cpuTimes2)
+}
+
+func percentUsedFromLastCall(percpu bool) ([]float64, error) {
+	cpuTimes, err := Times(percpu)
+	if err != nil {
+		return nil, err
+	}
+	lastCPUPercent.Lock()
+	defer lastCPUPercent.Unlock()
+	var lastTimes []TimesStat
+	if percpu {
+		lastTimes = lastCPUPercent.lastPerCPUTimes
+		lastCPUPercent.lastPerCPUTimes = cpuTimes
+	} else {
+		lastTimes = lastCPUPercent.lastCPUTimes
+		lastCPUPercent.lastCPUTimes = cpuTimes
 	}
 
-	ret := make([]float64, len(cpuTimes1))
-	for i, t := range cpuTimes2 {
-		ret[i] = calculate(cpuTimes1[i], t)
+	if lastTimes == nil {
+		return nil, fmt.Errorf("Error getting times for cpu percent. LastTimes was nil")
 	}
-	return ret, nil
+	return calcualteALLBusy(lastTimes, cpuTimes)
+
 }