Merge pull request #962 from AtakanColak/fix-ppid-race-961

Fix Windows Ppid Cache Race Condition

process/process.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"runtime"
 	"sort"
+	"sync"
 	"syscall"
 	"time"
 
@@ -26,6 +27,7 @@ type Process struct {
 	name           string
 	status         string
 	parent         int32
+	parentMutex    *sync.RWMutex // for windows ppid cache
 	numCtxSwitches *NumCtxSwitchesStat
 	uids           []int32
 	gids           []int32
@@ -167,7 +169,10 @@ func NewProcess(pid int32) (*Process, error) {
 }
 
 func NewProcessWithContext(ctx context.Context, pid int32) (*Process, error) {
-	p := &Process{Pid: pid}
+	p := &Process{
+		Pid:         pid,
+		parentMutex: new(sync.RWMutex),
+	}
 
 	exists, err := PidExistsWithContext(ctx, pid)
 	if err != nil {

process/process_race_test.go

@@ -0,0 +1,30 @@
+// +build race
+
+package process
+
+import (
+	"sync"
+	"testing"
+)
+
+func Test_Process_Ppid_Race(t *testing.T) {
+	wg := sync.WaitGroup{}
+	testCount := 10
+	p := testGetProcess()
+	wg.Add(testCount)
+	for i := 0; i < testCount; i++ {
+		go func(j int) {
+			ppid, err := p.Ppid()
+			wg.Done()
+			skipIfNotImplementedErr(t, err)
+			if err != nil {
+				t.Errorf("Ppid() failed, %v", err)
+			}
+
+			if j == 9 {
+				t.Logf("Ppid(): %d", ppid)
+			}
+		}(i)
+	}
+	wg.Wait()
+}

process/process_windows.go

@@ -237,8 +237,9 @@ func PidExistsWithContext(ctx context.Context, pid int32) (bool, error) {
 
 func (p *Process) PpidWithContext(ctx context.Context) (int32, error) {
 	// if cached already, return from cache
-	if p.parent != 0 {
+	cachedPpid := p.getPpid()
-		return p.parent, nil
+	if cachedPpid != 0 {
+		return cachedPpid, nil
 	}
 
 	ppid, _, _, err := getFromSnapProcess(p.Pid)
@@ -246,8 +247,8 @@ func (p *Process) PpidWithContext(ctx context.Context) (int32, error) {
 		return 0, err
 	}
 
-	// if no errors, cache it
+	// no errors and not cached already, so cache it
-	p.parent = ppid
+	p.setPpid(ppid)
 
 	return ppid, nil
 }
@@ -258,8 +259,11 @@ func (p *Process) NameWithContext(ctx context.Context) (string, error) {
 		return "", fmt.Errorf("could not get Name: %s", err)
 	}
 
-	// if no errors, cache ppid
+	// if no errors and not cached already, cache ppid
 	p.parent = ppid
+	if 0 == p.getPpid() {
+		p.setPpid(ppid)
+	}
 
 	return name, nil
 }
@@ -456,8 +460,11 @@ func (p *Process) NumThreadsWithContext(ctx context.Context) (int32, error) {
 		return 0, err
 	}
 
-	// if no errors, cache ppid
+	// if no errors and not cached already, cache ppid
 	p.parent = ppid
+	if 0 == p.getPpid() {
+		p.setPpid(ppid)
+	}
 
 	return ret, nil
 }
@@ -613,6 +620,21 @@ func (p *Process) KillWithContext(ctx context.Context) error {
 	return process.Kill()
 }
 
+// retrieve Ppid in a thread-safe manner
+func (p *Process) getPpid() int32 {
+	p.parentMutex.RLock()
+	defer p.parentMutex.RUnlock()
+	return p.parent
+}
+
+// cache Ppid in a thread-safe manner (WINDOWS ONLY)
+// see https://psutil.readthedocs.io/en/latest/#psutil.Process.ppid
+func (p *Process) setPpid(ppid int32) {
+	p.parentMutex.Lock()
+	defer p.parentMutex.Unlock()
+	p.parent = ppid
+}
+
 func getFromSnapProcess(pid int32) (int32, int32, string, error) {
 	snap, err := windows.CreateToolhelp32Snapshot(windows.TH32CS_SNAPPROCESS, uint32(pid))
 	if err != nil {