perf(proctree): remove stat call

Calling stat on /proc/<pid> would only increase the window for
process termination between the stat call and the read of the file.

This also replaces fmt.Sprintf with string concatenation and
strconv.FormatInt for better performance.

pkg/proctree/proctree_procfs.go

@@ -1,9 +1,9 @@
 package proctree
 
 import (
-	"fmt"
 	"math"
 	"os"
+	"strconv"
 	"sync"
 	"time"
 
@@ -128,12 +128,12 @@ func dealWithProc(pt *ProcessTree, givenPid int32) error {
 		},
 	)
 	if err != nil {
-		return errfmt.Errorf("%v", err)
+		return errfmt.WrapError(err)
 	}
 
 	status, err := proc.NewProcStatus(givenPid)
 	if err != nil {
-		return errfmt.Errorf("%v", err)
+		return errfmt.WrapError(err)
 	}
 	if status.GetPid() != status.GetTgid() {
 		return errfmt.Errorf("invalid process") // sanity check (process, not thread)
@@ -226,12 +226,12 @@ func dealWithThread(pt *ProcessTree, givenPid, givenTid int32) error {
 		},
 	)
 	if err != nil {
-		return errfmt.Errorf("%v", err)
+		return errfmt.WrapError(err)
 	}
 
 	status, err := proc.NewThreadProcStatus(givenPid, givenTid)
 	if err != nil {
-		return errfmt.Errorf("%v", err)
+		return errfmt.WrapError(err)
 	}
 
 	name := status.GetName()
@@ -308,38 +308,43 @@ func dealWithThread(pt *ProcessTree, givenPid, givenTid int32) error {
 
 // dealWithProcFsEntry deals with a process from procfs.
 func dealWithProcFsEntry(pt *ProcessTree, givenPid int32) error {
-	_, err := os.Stat(fmt.Sprintf("/proc/%v", givenPid))
-	if os.IsNotExist(err) {
-		return errfmt.Errorf("could not find process %v", givenPid)
-	}
-
-	err = dealWithProc(pt, givenPid) // run for the given process
+	err := dealWithProc(pt, givenPid) // run for the given process
 	if err != nil {
+		if os.IsNotExist(err) {
+			err = nil // ignore non-existent processes
+		}
 		if debugMsgs {
 			logger.Debugw("dealWithProc", "pid", givenPid, "err", err)
 		}
+
 		return err
 	}
 
-	taskPath := fmt.Sprintf("/proc/%v/task", givenPid)
+	taskPath := "/proc/" + strconv.FormatInt(int64(givenPid), 10) + "/task"
 	taskDirs, err := os.ReadDir(taskPath)
 	if err != nil {
 		return err
 	}
+
 	for _, taskDir := range taskDirs {
 		if !taskDir.IsDir() {
 			continue
 		}
+
 		tid, err := proc.ParseInt32(taskDir.Name())
 		if err != nil {
 			continue
 		}
 
 		err = dealWithThread(pt, givenPid, tid) // run for all threads of the given process
 		if err != nil {
+			if os.IsNotExist(err) {
+				err = nil // ignore non-existent threads
+			}
 			if debugMsgs {
 				logger.Debugw("dealWithThread", "pid", givenPid, "tid", tid, "err", err)
 			}
+
 			continue
 		}
 	}