process_collector: Add Platform-Specific Describe for processCollector

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Unreleased
 
+* [ENHANCEMENT] process_collector: Add Platform-Specific Describe for processCollector. #1625
+
 ## 1.20.2 / 2024-08-23
 
 * [BUGFIX] promhttp: Unset Content-Encoding header when data is uncompressed. #1596

prometheus/process_collector.go

@@ -23,6 +23,7 @@ import (
 
 type processCollector struct {
 	collectFn         func(chan<- Metric)
+	describeFn        func(chan<- *Desc)
 	pidFn             func() (int, error)
 	reportErrors      bool
 	cpuTotal          *Desc
@@ -122,33 +123,35 @@ func NewProcessCollector(opts ProcessCollectorOpts) Collector {
 	// Set up process metric collection if supported by the runtime.
 	if canCollectProcess() {
 		c.collectFn = c.processCollect
+		c.describeFn = c.describe
 	} else {
-		c.collectFn = func(ch chan<- Metric) {
-			c.reportError(ch, nil, errors.New("process metrics not supported on this platform"))
-		}
+		c.collectFn = c.defaultCollectFn
+		c.describeFn = c.defaultDescribeFn
 	}
 
 	return c
 }
 
-// Describe returns all descriptions of the collector.
-func (c *processCollector) Describe(ch chan<- *Desc) {
-	ch <- c.cpuTotal
-	ch <- c.openFDs
-	ch <- c.maxFDs
-	ch <- c.vsize
-	ch <- c.maxVsize
-	ch <- c.rss
-	ch <- c.startTime
-	ch <- c.inBytes
-	ch <- c.outBytes
+func (c *processCollector) defaultCollectFn(ch chan<- Metric) {
+	c.reportError(ch, nil, errors.New("process metrics not supported on this platform"))
+}
+
+func (c *processCollector) defaultDescribeFn(ch chan<- *Desc) {
+	if c.reportErrors {
+		ch <- NewInvalidDesc(errors.New("process metrics not supported on this platform"))
+	}
 }
 
 // Collect returns the current state of all metrics of the collector.
 func (c *processCollector) Collect(ch chan<- Metric) {
 	c.collectFn(ch)
 }
 
+// Describe returns all descriptions of the collector.
+func (c *processCollector) Describe(ch chan<- *Desc) {
+	c.describeFn(ch)
+}
+
 func (c *processCollector) reportError(ch chan<- Metric, desc *Desc, err error) {
 	if !c.reportErrors {
 		return

prometheus/process_collector_darwin.go

@@ -15,10 +15,11 @@ package prometheus
 
 import (
 	"fmt"
-	"golang.org/x/sys/unix"
 	"os"
 	"syscall"
 	"time"
+
+	"golang.org/x/sys/unix"
 )
 
 func canCollectProcess() bool {
@@ -58,6 +59,25 @@ func getOpenFileCount() (float64, error) {
 	}
 }
 
+// describe returns all descriptions of the collector for Darwin.
+// Ensure that this list of descriptors is kept in sync with the metrics collected
+// in the processCollect method. Any changes to the metrics in processCollect
+// (such as adding or removing metrics) should be reflected in this list of descriptors.
+func (c *processCollector) describe(ch chan<- *Desc) {
+	ch <- c.cpuTotal
+	ch <- c.openFDs
+	ch <- c.maxFDs
+	ch <- c.maxVsize
+	ch <- c.startTime
+
+	/* the process could be collected but not implemented yet
+	ch <- c.rss
+	ch <- c.vsize
+	ch <- c.inBytes
+	ch <- c.outBytes
+	*/
+}
+
 func (c *processCollector) processCollect(ch chan<- Metric) {
 	if procs, err := unix.SysctlKinfoProcSlice("kern.proc.pid", os.Getpid()); err == nil {
 		if len(procs) == 1 {

prometheus/process_collector_js.go

@@ -20,7 +20,14 @@ func canCollectProcess() bool {
 	return false
 }
 
+// describe returns all descriptions of the collector for js.
+// Ensure that this list of descriptors is kept in sync with the metrics collected
+// in the processCollect method. Any changes to the metrics in processCollect
+// (such as adding or removing metrics) should be reflected in this list of descriptors.
 func (c *processCollector) processCollect(ch chan<- Metric) {
-	// noop on this platform
-	return
+	c.defaultCollect(ch)
+}
+
+func (c *processCollector) describe(ch chan<- *Desc) {
+	c.defaultDescribe(ch)
 }

prometheus/process_collector_other.go

@@ -78,3 +78,19 @@ func (c *processCollector) processCollect(ch chan<- Metric) {
 		c.reportError(ch, nil, err)
 	}
 }
+
+// describe returns all descriptions of the collector for others than windows, js, wasip1 and darwin.
+// Ensure that this list of descriptors is kept in sync with the metrics collected
+// in the processCollect method. Any changes to the metrics in processCollect
+// (such as adding or removing metrics) should be reflected in this list of descriptors.
+func (c *processCollector) describe(ch chan<- *Desc) {
+	ch <- c.cpuTotal
+	ch <- c.openFDs
+	ch <- c.maxFDs
+	ch <- c.vsize
+	ch <- c.maxVsize
+	ch <- c.rss
+	ch <- c.startTime
+	ch <- c.inBytes
+	ch <- c.outBytes
+}

prometheus/process_collector_test.go

@@ -170,3 +170,52 @@ func TestNewPidFileFn(t *testing.T) {
 		}
 	}
 }
+
+func TestDescribeAndCollectAlignment(t *testing.T) {
+	collector := &processCollector{
+		pidFn:     getPIDFn(),
+		cpuTotal:  NewDesc("cpu_total", "Total CPU usage", nil, nil),
+		openFDs:   NewDesc("open_fds", "Number of open file descriptors", nil, nil),
+		maxFDs:    NewDesc("max_fds", "Maximum file descriptors", nil, nil),
+		vsize:     NewDesc("vsize", "Virtual memory size", nil, nil),
+		maxVsize:  NewDesc("max_vsize", "Maximum virtual memory size", nil, nil),
+		rss:       NewDesc("rss", "Resident Set Size", nil, nil),
+		startTime: NewDesc("start_time", "Process start time", nil, nil),
+		inBytes:   NewDesc("in_bytes", "Input bytes", nil, nil),
+		outBytes:  NewDesc("out_bytes", "Output bytes", nil, nil),
+	}
+
+	// Collect and get descriptors
+	descCh := make(chan *Desc, 15)
+	collector.describe(descCh)
+	close(descCh)
+
+	definedDescs := make(map[string]bool)
+	for desc := range descCh {
+		definedDescs[desc.String()] = true
+	}
+
+	// Collect and get metrics
+	metricsCh := make(chan Metric, 15)
+	collector.processCollect(metricsCh)
+	close(metricsCh)
+
+	collectedMetrics := make(map[string]bool)
+	for metric := range metricsCh {
+		collectedMetrics[metric.Desc().String()] = true
+	}
+
+	// Verify that all described metrics are collected
+	for desc := range definedDescs {
+		if !collectedMetrics[desc] {
+			t.Errorf("Metric %s described but not collected", desc)
+		}
+	}
+
+	// Verify that no extra metrics are collected
+	for desc := range collectedMetrics {
+		if !definedDescs[desc] {
+			t.Errorf("Metric %s collected but not described", desc)
+		}
+	}
+}

prometheus/process_collector_wasip1.go

@@ -20,7 +20,14 @@ func canCollectProcess() bool {
 	return false
 }
 
-func (*processCollector) processCollect(chan<- Metric) {
-	// noop on this platform
-	return
+func (c *processCollector) processCollect(ch chan<- Metric) {
+	c.defaultCollect(ch)
+}
+
+// describe returns all descriptions of the collector for wasip1.
+// Ensure that this list of descriptors is kept in sync with the metrics collected
+// in the processCollect method. Any changes to the metrics in processCollect
+// (such as adding or removing metrics) should be reflected in this list of descriptors.
+func (c *processCollector) describe(ch chan<- *Desc) {
+	c.defaultDescribe(ch)
 }

prometheus/process_collector_windows.go

@@ -79,14 +79,10 @@ func getProcessHandleCount(handle windows.Handle) (uint32, error) {
 }
 
 func (c *processCollector) processCollect(ch chan<- Metric) {
-	h, err := windows.GetCurrentProcess()
-	if err != nil {
-		c.reportError(ch, nil, err)
-		return
-	}
+	h := windows.CurrentProcess()
 
 	var startTime, exitTime, kernelTime, userTime windows.Filetime
-	err = windows.GetProcessTimes(h, &startTime, &exitTime, &kernelTime, &userTime)
+	err := windows.GetProcessTimes(h, &startTime, &exitTime, &kernelTime, &userTime)
 	if err != nil {
 		c.reportError(ch, nil, err)
 		return
@@ -111,6 +107,19 @@ func (c *processCollector) processCollect(ch chan<- Metric) {
 	ch <- MustNewConstMetric(c.maxFDs, GaugeValue, float64(16*1024*1024)) // Windows has a hard-coded max limit, not per-process.
 }
 
+// describe returns all descriptions of the collector for windows.
+// Ensure that this list of descriptors is kept in sync with the metrics collected
+// in the processCollect method. Any changes to the metrics in processCollect
+// (such as adding or removing metrics) should be reflected in this list of descriptors.
+func (c *processCollector) describe(ch chan<- *Desc) {
+	ch <- c.cpuTotal
+	ch <- c.openFDs
+	ch <- c.maxFDs
+	ch <- c.vsize
+	ch <- c.rss
+	ch <- c.startTime
+}
+
 func fileTimeToSeconds(ft windows.Filetime) float64 {
 	return float64(uint64(ft.HighDateTime)<<32+uint64(ft.LowDateTime)) / 1e7
 }

prometheus/process_collector_windows_test.go

@@ -68,3 +68,52 @@ func TestWindowsProcessCollector(t *testing.T) {
 		}
 	}
 }
+
+func TestWindowsDescribeAndCollectAlignment(t *testing.T) {
+	collector := &processCollector{
+		pidFn:     getPIDFn(),
+		cpuTotal:  NewDesc("cpu_total", "Total CPU usage", nil, nil),
+		openFDs:   NewDesc("open_fds", "Number of open file descriptors", nil, nil),
+		maxFDs:    NewDesc("max_fds", "Maximum file descriptors", nil, nil),
+		vsize:     NewDesc("vsize", "Virtual memory size", nil, nil),
+		maxVsize:  NewDesc("max_vsize", "Maximum virtual memory size", nil, nil),
+		rss:       NewDesc("rss", "Resident Set Size", nil, nil),
+		startTime: NewDesc("start_time", "Process start time", nil, nil),
+		inBytes:   NewDesc("in_bytes", "Input bytes", nil, nil),
+		outBytes:  NewDesc("out_bytes", "Output bytes", nil, nil),
+	}
+
+	// Collect and get descriptors
+	descCh := make(chan *Desc, 15)
+	collector.describe(descCh)
+	close(descCh)
+
+	definedDescs := make(map[string]bool)
+	for desc := range descCh {
+		definedDescs[desc.String()] = true
+	}
+
+	// Collect and get metrics
+	metricsCh := make(chan Metric, 15)
+	collector.processCollect(metricsCh)
+	close(metricsCh)
+
+	collectedMetrics := make(map[string]bool)
+	for metric := range metricsCh {
+		collectedMetrics[metric.Desc().String()] = true
+	}
+
+	// Verify that all described metrics are collected
+	for desc := range definedDescs {
+		if !collectedMetrics[desc] {
+			t.Errorf("Metric %s described but not collected", desc)
+		}
+	}
+
+	// Verify that no extra metrics are collected
+	for desc := range collectedMetrics {
+		if !definedDescs[desc] {
+			t.Errorf("Metric %s collected but not described", desc)
+		}
+	}
+}