@@ -66,7 +55,7 @@ Each queue control block contains information about the queue status.
- The queue ID is returned if a queue is created successfully.
- The queue control block contains **Head** and **Tail**, which indicate the storage status of messages in a queue. **Head** indicates the start position of occupied message nodes in the queue. **Tail** indicates the end position of the occupied message nodes and the start position of idle message nodes. When a queue is created, **Head** and **Tail** point to the start position of the queue.
- When data is to be written to a queue, **readWriteableCnt\[1\]** is used to determine whether data can be written to the queue. If **readWriteableCnt\[1\]** is **0**, the queue is full and data cannot be written to it. Data can be written to the head node or tail node of a queue. To write data to the tail node, locate the start idle message node based on **Tail** and write data to it. If **Tail** is pointing to the tail of the queue, the rewind mode is used. To write data to the head node, locate previous node based on **Head** and write data to it. If **Head** is pointing to the start position of the queue, the rewind mode is used.
- When a queue is to be read, **readWriteableCnt\[0\]** is used to determine whether the queue has messages to read. Reading an idle queue \(**readWriteableCnt\[0\]** is** 0**\) will cause task suspension. If the queue has messages to read, the system locates the first node to which data is written based on **Head** and read the message from the node. If **Head** is pointing to the tail of the queue, the rewind mode is used.
- When a queue is to be read, **readWriteableCnt\[0\]** is used to determine whether the queue has messages to read. Reading an idle queue \(**readWriteableCnt\[0\]** is **0**\) will cause task suspension. If the queue has messages to read, the system locates the first node to which data is written based on **Head** and read the message from the node. If **Head** is pointing to the tail of the queue, the rewind mode is used.
- When a queue is to be deleted, the system locates the queue based on the queue ID, sets the queue status to **OS\_QUEUE\_UNUSED**, sets the queue control block to the initial state, and releases the memory occupied by the queue.
**Figure 1** Reading and writing data in a queue<aname="fig1343517592468"></a>
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@@ -155,7 +144,7 @@ The preceding figure illustrates how to write data to the tail node only. Writin
>- The input parameter **timeOut** in the queue interface function is relative time.
>- **LOS\_QueueReadCopy**, **LOS\_QueueWriteCopy**, and **LOS\_QueueWriteHeadCopy** are a group of APIs that must be used together. **LOS\_QueueRead**, **LOS\_QueueWrite**, and **LOS\_QueueWriteHead** are a group of APIs that must be used together.
>- As **LOS\_QueueWrite**, **LOS\_QueueWriteHead**, and **LOS\_QueueRead** are used to manage data addresses, you must ensure that the memory directed by the pointer obtained by calling **LOS\_QueueRead** is not modified or released abnormally when the queue is being read. Otherwise, unpredictable results may occur.
>- If the input parameter bufferSize in **LOS\_QueueReadCopy** is less than the actual length of the message, the message will be truncated.
>- If the input parameter **bufferSize** in **LOS\_QueueReadCopy** is less than the length of the message, the message will be truncated.
>- **LOS\_QueueWrite**, **LOS\_QueueWriteHead**, and **LOS\_QueueRead** are called to manage data addresses, which means that the actual data read or written is pointer data. Therefore, before using these APIs, ensure that the message node size is the pointer length during queue creation, to avoid waste and read failures.
## Development Example<a name="section460018317164"></a>
@@ -156,7 +142,7 @@ The preceding figure illustrates how to write data to the tail node only. Writin
>- The input parameter **timeOut** in the queue interface function is relative time.
>- **LOS\_QueueReadCopy**, **LOS\_QueueWriteCopy**, and **LOS\_QueueWriteHeadCopy** are a group of APIs that must be used together. **LOS\_QueueRead**, **LOS\_QueueWrite**, and **LOS\_QueueWriteHead** are a group of APIs that must be used together.
>- As **LOS\_QueueWrite**, **LOS\_QueueWriteHead**, and **LOS\_QueueRead** are used to manage data addresses, you must ensure that the memory directed by the pointer obtained by calling **LOS\_QueueRead** is not modified or released abnormally when the queue is being read. Otherwise, unpredictable results may occur.
>- If the input parameter bufferSize in **LOS\_QueueRead**and**LOS\_QueueReadCopy** is less than the actual length of the message, the message will be truncated.
>- If the input parameter **bufferSize** in **LOS\_QueueRead** and **LOS\_QueueReadCopy** is less than the length of the message, the message will be truncated.
>- **LOS\_QueueWrite**, **LOS\_QueueWriteHead**, and **LOS\_QueueRead** are called to manage data addresses, which means that the actual data read or written is pointer data. Therefore, before using these APIs, ensure that the message node size is the pointer length during queue creation, to avoid waste and read failures.
## Development Example<a name="section27132341285"></a>
