use state machine management for exec.Pid()

Signed-off-by: Lifubang <lifubang@acmcoder.com>

runtime/v1/linux/proc/exec.go

@@ -69,8 +69,10 @@ func (e *execProcess) ID() string {
 }
 
 func (e *execProcess) Pid() int {
-	e.mu.Lock()
-	defer e.mu.Unlock()
+	return e.execState.Pid()
+}
+
+func (e *execProcess) pidv() int {
 	return e.pid
 }