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Perform atomic message write in prvWriteMessageToBuffer

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This commit is contained in:
Miles Frain 2021-02-18 15:08:00 -08:00
parent cda43dd4d8
commit ee82c9f34b
1 changed files with 19 additions and 10 deletions
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29
stream_buffer.c
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@ -160,12 +160,19 @@ static size_t prvBytesInBuffer( const StreamBuffer_t * const pxStreamBuffer ) PR
/* /*
* Add xCount bytes from pucData into the pxStreamBuffer's data storage area. * Add xCount bytes from pucData into the pxStreamBuffer's data storage area.
* Assumes there is enough free space in the buffer. * This function does not update the buffer's xHead pointer, so multiple writes
* Always returns xCount, which is the number of bytes written. * may be chained together "atomically". This is useful for Message Buffers where
* the length and data bytes are written in two separate chunks, and we don't want
* the reader to see the buffer as having grown until after all data is copied over.
* This function takes a custom xHead value to indicate where to write to (necessary
* for chaining) and returns the the resulting xHead position.
* To mark the write as complete, manually set the buffer's xHead field with the
* returned xHead from this function.
*/ */
static size_t prvWriteBytesToBuffer( StreamBuffer_t * const pxStreamBuffer, static size_t prvWriteBytesToBuffer( StreamBuffer_t * const pxStreamBuffer,
const uint8_t * pucData, const uint8_t * pucData,
size_t xCount ) PRIVILEGED_FUNCTION; size_t xCount,
size_t xHead ) PRIVILEGED_FUNCTION;
/* /*
* If the stream buffer is being used as a message buffer, then reads an entire * If the stream buffer is being used as a message buffer, then reads an entire
@ -704,6 +711,7 @@ static size_t prvWriteMessageToBuffer( StreamBuffer_t * const pxStreamBuffer,
{ {
BaseType_t xShouldWrite; BaseType_t xShouldWrite;
size_t xReturn; size_t xReturn;
size_t xNextHead = pxStreamBuffer->xHead;
if( xSpace == ( size_t ) 0 ) if( xSpace == ( size_t ) 0 )
{ {
@ -726,7 +734,7 @@ static size_t prvWriteMessageToBuffer( StreamBuffer_t * const pxStreamBuffer,
* into the buffer. Start by writing the length of the data, the data * into the buffer. Start by writing the length of the data, the data
* itself will be written later in this function. */ * itself will be written later in this function. */
xShouldWrite = pdTRUE; xShouldWrite = pdTRUE;
( void ) prvWriteBytesToBuffer( pxStreamBuffer, ( const uint8_t * ) &( xDataLengthBytes ), sbBYTES_TO_STORE_MESSAGE_LENGTH ); xNextHead = prvWriteBytesToBuffer( pxStreamBuffer, ( const uint8_t * ) &( xDataLengthBytes ), sbBYTES_TO_STORE_MESSAGE_LENGTH, xNextHead);
} }
else else
{ {
@ -737,7 +745,9 @@ static size_t prvWriteMessageToBuffer( StreamBuffer_t * const pxStreamBuffer,
if( xShouldWrite != pdFALSE ) if( xShouldWrite != pdFALSE )
{ {
/* Writes the data itself. */ /* Writes the data itself. */
xReturn = prvWriteBytesToBuffer( pxStreamBuffer, ( const uint8_t * ) pvTxData, xDataLengthBytes ); /*lint !e9079 Storage buffer is implemented as uint8_t for ease of sizing, alignment and access. */ xNextHead = prvWriteBytesToBuffer( pxStreamBuffer, ( const uint8_t * ) pvTxData, xDataLengthBytes, xNextHead ); /*lint !e9079 Storage buffer is implemented as uint8_t for ease of sizing, alighment and access. */
pxStreamBuffer->xHead = xNextHead;
xReturn = xDataLengthBytes;
} }
else else
{ {
@ -1129,13 +1139,14 @@ BaseType_t xStreamBufferReceiveCompletedFromISR( StreamBufferHandle_t xStreamBuf
static size_t prvWriteBytesToBuffer( StreamBuffer_t * const pxStreamBuffer, static size_t prvWriteBytesToBuffer( StreamBuffer_t * const pxStreamBuffer,
const uint8_t * pucData, const uint8_t * pucData,
size_t xCount ) size_t xCount,
size_t xHead )
{ {
size_t xNextHead, xFirstLength; size_t xNextHead, xFirstLength;
configASSERT( xCount > ( size_t ) 0 ); configASSERT( xCount > ( size_t ) 0 );
xNextHead = pxStreamBuffer->xHead; xNextHead = xHead;
/* Calculate the number of bytes that can be added in the first write - /* Calculate the number of bytes that can be added in the first write -
* which may be less than the total number of bytes that need to be added if * which may be less than the total number of bytes that need to be added if
@ -1170,9 +1181,7 @@ static size_t prvWriteBytesToBuffer( StreamBuffer_t * const pxStreamBuffer,
mtCOVERAGE_TEST_MARKER(); mtCOVERAGE_TEST_MARKER();
} }
pxStreamBuffer->xHead = xNextHead; return xNextHead;
return xCount;
} }
/*-----------------------------------------------------------*/ /*-----------------------------------------------------------*/