proc/native: race between RequestManualStop and trapWait

RequestManualStop will run concurrently with trapWait, since one writes
dbp.halt and the other reads it dbp.halt should be protected by a
mutex.

Updates #830

pkg/proc/native/proc.go

@@ -37,6 +37,7 @@ type Process struct {
 	breakpointIDCounter         int
 	internalBreakpointIDCounter int
 	firstStart                  bool
+	haltMu                      sync.Mutex
 	halt                        bool
 	exited                      bool
 	ptraceChan                  chan func()
@@ -187,6 +188,8 @@ func (dbp *Process) RequestManualStop() error {
 	if dbp.exited {
 		return &proc.ProcessExitedError{}
 	}
+	dbp.haltMu.Lock()
+	defer dbp.haltMu.Unlock()
 	dbp.halt = true
 	return dbp.requestManualStop()
 }

pkg/proc/native/proc_darwin.go

@@ -291,7 +291,10 @@ func (dbp *Process) trapWait(pid int) (*Thread, error) {
 			return nil, proc.ProcessExitedError{Pid: dbp.pid, Status: status.ExitStatus()}
 
 		case C.MACH_RCV_INTERRUPTED:
-			if !dbp.halt {
+			dbp.haltMu.Lock()
+			halt := dbp.halt
+			dbp.haltMu.Unlock()
+			if !halt {
 				// Call trapWait again, it seems
 				// MACH_RCV_INTERRUPTED is emitted before
 				// process natural death _sometimes_.
@@ -319,7 +322,10 @@ func (dbp *Process) trapWait(pid int) (*Thread, error) {
 		dbp.updateThreadList()
 		th, ok := dbp.threads[int(port)]
 		if !ok {
-			if dbp.halt {
+			dbp.haltMu.Lock()
+			halt := dbp.halt
+			dbp.haltMu.Unlock()
+			if halt {
 				dbp.halt = false
 				return th, nil
 			}

pkg/proc/native/proc_linux.go

@@ -236,7 +236,10 @@ func (dbp *Process) trapWait(pid int) (*Thread, error) {
 			// Sometimes we get an unknown thread, ignore it?
 			continue
 		}
-		if status.StopSignal() == sys.SIGTRAP && dbp.halt {
+		dbp.haltMu.Lock()
+		halt := dbp.halt
+		dbp.haltMu.Unlock()
+		if status.StopSignal() == sys.SIGTRAP && halt {
 			th.running = false
 			dbp.halt = false
 			return th, nil