diff --git a/notxv6/ph.c b/notxv6/ph.c
index 82afe76..a09951d 100644
--- a/notxv6/ph.c
+++ b/notxv6/ph.c
@@ -17,6 +17,8 @@ struct entry *table[NBUCKET];
 int keys[NKEYS];
 int nthread = 1;
 
+pthread_mutex_t lock[NBUCKET]; // lock for puts
+
 
 double
 now()
@@ -31,7 +33,7 @@ insert(int key, int value, struct entry **p, struct entry *n)
 {
   struct entry *e = malloc(sizeof(struct entry));
   e->key = key;
-  e->value = value;
+  e->value = value; 
   e->next = n;
   *p = e;
 }
@@ -51,8 +53,11 @@ void put(int key, int value)
     // update the existing key.
     e->value = value;
   } else {
+  pthread_mutex_lock(&lock[i]);
     // the new is new.
+    // 重要的是 table[i] 的值，如果 thread1 刚进入，但是 thread_2 已经修改了 table[i] 此时就会丢失后面的所有node
     insert(key, value, &table[i], table[i]);
+  pthread_mutex_unlock(&lock[i]);
   }
 
 }
@@ -118,6 +123,9 @@ main(int argc, char *argv[])
     keys[i] = random();
   }
 
+  for (int i = 0; i < NBUCKET; ++i)
+    pthread_mutex_init(&lock[i], NULL);
+
   //
   // first the puts
   //