Keep a cache of open files, reducing the number of open/close cycles in the /proc dir

probe/proc/reader_linux_test.go

@@ -1,24 +1,37 @@
 package proc_test
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"reflect"
 	"strconv"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/weaveworks/scope/probe/proc"
 	"github.com/weaveworks/scope/test"
 )
 
+type mockedProcess struct {
+	ID, Comm, Cmdline string
+}
+
+func (p mockedProcess) Name() string       { return p.ID }
+func (p mockedProcess) Size() int64        { return 0 }
+func (p mockedProcess) Mode() os.FileMode  { return 0 }
+func (p mockedProcess) ModTime() time.Time { return time.Now() }
+func (p mockedProcess) IsDir() bool        { return true }
+func (p mockedProcess) Sys() interface{}   { return nil }
+
 func TestProcReaderProcesses(t *testing.T) {
-	processes := map[string]proc.MockedProcess{
-		"3":       {Id: "3", Comm: "curl\n", Cmdline: "curl\000google.com"},
-		"2":       {Id: "2", Comm: "bash\n"},
-		"4":       {Id: "4", Comm: "apache\n"},
-		"notapid": {Id: "notapid"},
-		"1":       {Id: "1", Comm: "init\n"},
+	processes := map[string]mockedProcess{
+		"3":       {ID: "3", Comm: "curl\n", Cmdline: "curl\000google.com"},
+		"2":       {ID: "2", Comm: "bash\n"},
+		"4":       {ID: "4", Comm: "apache\n"},
+		"notapid": {ID: "notapid"},
+		"1":       {ID: "1", Comm: "init\n"},
 	}
 
 	want := map[int]proc.Process{
@@ -29,17 +42,16 @@ func TestProcReaderProcesses(t *testing.T) {
 	}
 
 	// use a mocked /proc that reads from our mocked processes
-	procDir := proc.MockedProcDir{
-		ReadDirFunc: func(path string) ([]os.FileInfo, error) {
-			result := []os.FileInfo{}
-			for _, p := range processes {
-				result = append(result, p)
+	procDir := mockedDir{
+		ReadDirNamesFunc: func(path string) ([]string, error) {
+			result := []string{}
+			for k := range processes {
+				result = append(result, k)
 			}
 			return result, nil
 		},
-
-		ReadFileFunc: func(path string) ([]byte, error) {
-			splits := strings.Split(path, "/")
+		OpenFunc: func(filename string) (proc.File, error) {
+			splits := strings.Split(filename, "/")
 			pid := splits[len(splits)-2]
 			process, ok := processes[pid]
 			if !ok {
@@ -47,22 +59,30 @@ func TestProcReaderProcesses(t *testing.T) {
 			}
 
 			file := splits[len(splits)-1]
+			var content []byte
 			switch file {
 			case "comm":
-				return []byte(process.Comm), nil
+				content = []byte(process.Comm)
 			case "stat":
 				pid, _ := strconv.Atoi(splits[len(splits)-2])
 				parent := pid - 1
-				return []byte(fmt.Sprintf("%d na R %d 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1", pid, parent)), nil
+				content = []byte(fmt.Sprintf("%d na R %d 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1", pid, parent))
 			case "cmdline":
-				return []byte(process.Cmdline), nil
+				content = []byte(process.Cmdline)
+			default:
+				return nil, fmt.Errorf("not found")
 			}
 
-			return nil, fmt.Errorf("not found")
+			return mockedFile{
+				ReadIntoFunc: func(buf *bytes.Buffer) error {
+					_, err := buf.Write(content)
+					return err
+				},
+			}, nil
 		},
 	}
 
-	procReader := proc.NewProcReader(procDir)
+	procReader := proc.NewReader(procDir)
 	have := map[int]proc.Process{}
 	err := procReader.Processes(func(p proc.Process) {
 		have[p.PID] = p