Update README.md

README.md

@@ -40,10 +40,12 @@ Unless otherwise specified, return the value before the memory operation
 Complex Commands
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 - **rwlock(stat, mut, block)**:
-  - **block**: Enable block polling until locked
+  - **block**: Enable block polling until locked (change `@counter`)
   - **mut**: Acquire write lock (default is read lock)
   - **result**: Guard value, please subtract the value of guard when releasing the lock
 
+    **Guard value by zero is acquire lock failed**
+
 
 Basic Usage Examples
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@@ -68,6 +70,8 @@ old: 3, changed: 7
 Simple Mutex Examples
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+`lock` can also be used, which is more simple and supports multiple read locks
+
 - `m == 0` is released
 - `m == 1` is acquired