[process][posix] Fix #607 check pid existence with a signal instead of listing every pids

Reference 0d6b91e916/lockfile_unix.go

process/process.go

@@ -139,21 +139,6 @@ func PidExists(pid int32) (bool, error) {
 	return PidExistsWithContext(context.Background(), pid)
 }
 
-func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
-	pids, err := Pids()
-	if err != nil {
-		return false, err
-	}
-
-	for _, i := range pids {
-		if i == pid {
-			return true, err
-		}
-	}
-
-	return false, err
-}
-
 // Background returns true if the process is in background, false otherwise.
 func (p *Process) Background() (bool, error) {
 	return p.BackgroundWithContext(context.Background())

process/process_fallback.go

@@ -48,6 +48,21 @@ func NewProcess(pid int32) (*Process, error) {
 	return nil, common.ErrNotImplementedError
 }
 
+func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
+	pids, err := PidsWithContext(ctx)
+	if err != nil {
+		return false, err
+	}
+
+	for _, i := range pids {
+		if i == pid {
+			return true, err
+		}
+	}
+
+	return false, err
+}
+
 func (p *Process) Ppid() (int32, error) {
 	return p.PpidWithContext(context.Background())
 }

process/process_posix.go

@@ -4,6 +4,7 @@ package process
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"os/user"
 	"path/filepath"
@@ -69,6 +70,34 @@ func getTerminalMap() (map[uint64]string, error) {
 	return ret, nil
 }
 
+func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
+	if pid <= 0 {
+		return false, fmt.Errorf("invalid pid %v", pid)
+	}
+	proc, err := os.FindProcess(int(pid))
+	if err != nil {
+		return false, err
+	}
+	err = proc.Signal(syscall.Signal(0))
+	if err == nil {
+		return true, nil
+	}
+	if err.Error() == "os: process already finished" {
+		return false, nil
+	}
+	errno, ok := err.(syscall.Errno)
+	if !ok {
+		return false, err
+	}
+	switch errno {
+	case syscall.ESRCH:
+		return false, nil
+	case syscall.EPERM:
+		return true, nil
+	}
+	return false, err
+}
+
 // SendSignal sends a unix.Signal to the process.
 // Currently, SIGSTOP, SIGCONT, SIGTERM and SIGKILL are supported.
 func (p *Process) SendSignal(sig syscall.Signal) error {

process/process_windows.go

@@ -185,6 +185,21 @@ func PidsWithContext(ctx context.Context) ([]int32, error) {
 
 }
 
+func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
+	pids, err := Pids()
+	if err != nil {
+		return false, err
+	}
+
+	for _, i := range pids {
+		if i == pid {
+			return true, err
+		}
+	}
+
+	return false, err
+}
+
 func (p *Process) Ppid() (int32, error) {
 	return p.PpidWithContext(context.Background())
 }