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receiving corrupt data with xQueueReceive

Posted by Mohammad on September 30, 2012
Hi everyone,
i have the following problem:
i dont receive the same data with xQueueReceive, that i sent it with the xQueueSend.
here is the code, maybe someone can help me solving the problem:

void privateMenuCreateRefreshEvent(unsigned char pattern, unsigned char field, unsigned int sensor, unsigned char value)
{
struct Display_Message SendMessage;
struct DataFieldUpdate *pointer = malloc(sizeof(struct DataFieldUpdate));
pointer->fieldNumber = 0;
pointer->patternType = 0;
pointer->valueID = 0;
pointer->valuetype = 0;
SendMessage.DataFieldObject = pointer;
SendMessage.Msg_Type = ProtocolData_Object;

xQueueSend(xDisplayQueue,&SendMessage,0);
free(pointer);
}

and the receiving task:

void dplTask(void *pvParameters)
{

for (;;)
{
struct Display_Message *ReceivedMessage = malloc(sizeof(struct Display_Message));;
xQueueReceive(xDisplayQueue,ReceivedMessage,portMAX_DELAY);
if ( ReceivedMessage->Msg_Type == ProtocolData_Object )
{
dplUpdateDisplayExecuteFunction(ReceivedMessage->DataFieldObject);
free(ReceivedMessage);
}
}
}

the ReceivedMessage->DataFieldObject dont have the same values that are sent in the example above.

what could be the problem here.

Best Regards.

RE: receiving corrupt data with xQueueReceive

Posted by Richard Damon on October 1, 2012
When you queue up SendMessage, the contents of the structure itself are copied into the queue, which will include the value of the pointer SendMessage.DataFieldObject. It does NOT make a copy of the DataFieldUpdate object. When you then do the free(pointer) the memory holding the values are returned to the heap, and possibly overwritten.

You should NOT do the free(pointer) at the sending side, but leave the DataFieldUpdate object on the heap, and when the data is received and processed, you then free the object on the receive side before the free(ReceviedMessage).

RE: receiving corrupt data with xQueueReceive

Posted by Mohammad on October 1, 2012
thank you very much richard.
i changed the struct Display_Message SendMessage and made the DataFieldObject in it not as a pointer. because i need about 30 queue-item for this queue and some items must wait until they will be processed. and now it is working very well.
thanks again.


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