161         let mut guard = result.inner.lock();  in new()  localVariable
162         guard.self_ref = Arc::downgrade(&result);  in new()
164         drop(guard); //这一步其实不需要，只要离开作用域，guard生命周期结束，自会解锁  in new()
281         let mut guard = self.inner.lock();  in open()  localVariable
287             guard.reader += 1;  in open()
290             guard.writer += 1;  in open()
314         let mut guard = self.inner.lock();  in close()  localVariable
318             assert!(guard.writer > 0);  in close()
319             guard.writer -= 1;  in close()
321             if guard.writer == 0 {  in close()
329             assert!(guard.reader > 0);  in close()
330             guard.reader -= 1;  in close()
332             if guard.reader == 0 {  in close()