proc/native/linux: call waitFast instead of wait in addThread and halt (#855)

The condition that causes waitFast to fail can not happen in addThread
and halt so we don't need to call the slower wait.

pkg/proc/native/proc_linux.go

@@ -120,7 +120,7 @@ func (dbp *Process) addThread(tid int, attach bool) (*Thread, error) {
 			// if we truly don't have permissions.
 			return nil, fmt.Errorf("could not attach to new thread %d %s", tid, err)
 		}
-		pid, status, err := dbp.wait(tid, 0)
+		pid, status, err := dbp.waitFast(tid)
 		if err != nil {
 			return nil, err
 		}
@@ -131,7 +131,7 @@ func (dbp *Process) addThread(tid int, attach bool) (*Thread, error) {
 
 	dbp.execPtraceFunc(func() { err = syscall.PtraceSetOptions(tid, syscall.PTRACE_O_TRACECLONE) })
 	if err == syscall.ESRCH {
-		if _, _, err = dbp.wait(tid, 0); err != nil {
+		if _, _, err = dbp.waitFast(tid); err != nil {
 			return nil, fmt.Errorf("error while waiting after adding thread: %d %s", tid, err)
 		}
 		dbp.execPtraceFunc(func() { err = syscall.PtraceSetOptions(tid, syscall.PTRACE_O_TRACECLONE) })

pkg/proc/native/threads_linux.go

@@ -22,7 +22,7 @@ func (t *Thread) halt() (err error) {
 		err = fmt.Errorf("halt err %s on thread %d", err, t.ID)
 		return
 	}
-	_, _, err = t.dbp.wait(t.ID, 0)
+	_, _, err = t.dbp.waitFast(t.ID)
 	if err != nil {
 		err = fmt.Errorf("wait err %s on thread %d", err, t.ID)
 		return