xQueueOverwrite
[队列管理]
queue.h
BaseType_t xQueueOverwrite(
QueueHandle_t xQueue,
const void * pvItemToQueue
);
这是用于调用 xQueueGenericSend() 函数的宏。
即使队列已满的情况下也将写入队列的 xQueueSendToBack() 版本，
同时覆盖队列中已经
存在的数据。
xQueueOverwrite() 旨在用于长度为 1 的队列，
这意味着队列要么为空，要么为满。
不得从中断服务程序 (ISR) 调用此函数。
请参阅 xQueueOverwriteFromISR()，了解可在 ISR 中使用的替代函数。
- 参数：
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xQueue
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接收发送数据的队列的句柄。
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pvItemToQueue
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指向待入队数据项的指针。队列
队列可容纳的项数在
创建队列时定义，这些项
将从 pvItemToQueue 复制到队列存储区域。
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-
返回：
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xQueueOverwrite() 是用于调用 xQueueGenericSend() 的宏，
因此与
xQueueSendToFront() 具有相同的返回值。 不过，由于
xQueueOverwrite() 将写入队列（即使队列已满），
pdPASS 是唯一可以返回的值。
用法示例：
void vFunction( void *pvParameters )
{
QueueHandle_t xQueue;
unsigned long ulVarToSend, ulValReceived;
/* Create a queue to hold one unsigned long value. It is strongly
recommended *not* to use xQueueOverwrite() on queues that can
contain more than one value, and doing so will trigger an assertion
if configASSERT() is defined. */
xQueue = xQueueCreate( 1, sizeof( unsigned long ) );
/* Write the value 10 to the queue using xQueueOverwrite(). */
ulVarToSend = 10;
xQueueOverwrite( xQueue, &ulVarToSend );
/* Peeking the queue should now return 10, but leave the value 10 in
the queue. A block time of zero is used as it is known that the
queue holds a value. */
ulValReceived = 0;
xQueuePeek( xQueue, &ulValReceived, 0 );
if( ulValReceived != 10 )
{
/* Error, unless another task removed the value. */
}
/* The queue is still full. Use xQueueOverwrite() to overwrite the
value held in the queue with 100. */
ulVarToSend = 100;
xQueueOverwrite( xQueue, &ulVarToSend );
/* This time read from the queue, leaving the queue empty once more.
A block time of 0 is used again. */
xQueueReceive( xQueue, &ulValReceived, 0 );
/* The value read should be the last value written, even though the
queue was already full when the value was written. */
if( ulValReceived != 100 )
{
/* Error unless another task is using the same queue. */
}
/* ... */
}
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