[GitHub] [apisix-dashboard] freecodelover commented on a change in pull request #2054: fix: perform pid lookup for existing pid file

[GitBox <gi...@apache.org>]

freecodelover commented on a change in pull request #2054:
URL: https://github.com/apache/apisix-dashboard/pull/2054#discussion_r709752587



##########
File path: api/internal/utils/pid.go
##########
@@ -18,19 +18,62 @@
 package utils
 
 import (
+	"bytes"
 	"fmt"
 	"io/ioutil"
 	"os"
+	"runtime"
 	"strconv"
+	"syscall"
+	"time"
+
+	"github.com/pkg/errors"
 )
 
 // WritePID write pid to the given file path.
 func WritePID(filepath string, forceStart bool) error {
-	if pid, err := ReadPID(filepath); err == nil {
-		if !forceStart {
-			return fmt.Errorf("Instance of Manager API maybe running with a pid %d. If not, please run Manager API with '-f' or '--force' flag\n", pid)
+	pidStatAction := func() error {
+		pid, err := ReadPID(filepath)
+		if err != nil {
+			return nil
+		}
+		// In unix system this always succeeds, doesn't ensure if the process at all exist or not.
+		proc, err := os.FindProcess(pid)
+		if err != nil {
+			return errors.Errorf("instance of Manager API maybe running with a pid %d. If not, please run Manager API with '-f' or '--force' flag. Error :%v\n", pid, err)
+		}
+
+		// Traditional unix way to check the existence of the particular PID.
+		err = proc.Signal(syscall.Signal(0))
+		// No entry of the process in process control block.
+		if err != nil {
+			return nil
+		}
+
+		// Windows has a tendency to pick unused old PIDs and allocate that to new process, so we won't kill it.
+		if runtime.GOOS != "windows" && forceStart {
+			fmt.Println("Killing existing instance of Manager API")

Review comment:
       It would be better to add the pid into the message.

##########
File path: api/internal/utils/pid.go
##########
@@ -18,19 +18,62 @@
 package utils
 
 import (
+	"bytes"
 	"fmt"
 	"io/ioutil"
 	"os"
+	"runtime"
 	"strconv"
+	"syscall"
+	"time"
+
+	"github.com/pkg/errors"
 )
 
 // WritePID write pid to the given file path.
 func WritePID(filepath string, forceStart bool) error {
-	if pid, err := ReadPID(filepath); err == nil {
-		if !forceStart {
-			return fmt.Errorf("Instance of Manager API maybe running with a pid %d. If not, please run Manager API with '-f' or '--force' flag\n", pid)
+	pidStatAction := func() error {
+		pid, err := ReadPID(filepath)
+		if err != nil {
+			return nil
+		}
+		// In unix system this always succeeds, doesn't ensure if the process at all exist or not.
+		proc, err := os.FindProcess(pid)
+		if err != nil {
+			return errors.Errorf("instance of Manager API maybe running with a pid %d. If not, please run Manager API with '-f' or '--force' flag. Error :%v\n", pid, err)

Review comment:
       I think `os. FindProcess` will return an error when the process does not exist in windows according to:
   https://golang.org/src/os/exec_windows.go
   
   So, we should not return the error here?




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