Tamas Szekeres wrote:
Hi All,
Upon thinking about the issues I've been come up with previously, I
consider the following approach could be implemented easily either at
driver or at SWIG interface level. Requires a new class to be
implemented by the async IO supported drivers and a new additional
method should be added to the GDALDataset and GDALRasterBand.
The user could implement the async IO by using the following pseudo sequence:
<Code>
...
</Code>
I like it :)
typedef enum {
...,
CE_Again = 5 // timeout, buffer not updated, call RasterIO() again
} CPLErr;
typedef enum { // Async raster io status
GRS_Complete = 0, // raster io is complete, call to
GDALRasterIOContext->RasterIO() will return CE_Failure
GRS_InProgress = 1, // raster io in progress, call
GDALRasterIOContext->RasterIO() to get more data
GRS_Error = 2 // error, call to GDALRasterIOContext->RasterIO()
will return CE_Failure
} GDALRasterIOStatus;
typedef enum { // Hints for GDALRasterIOContext->RasterIO(), driver
implementations may ignore any or all
GRH_SingleBlock = 0x1, // exit after single block update, even if
there is more data immediately available
GRH_Progressive = 0x2, // update with lower resolution data / fill
with interlaced rows
GRH_WaitForTimeout = 0x4 // wait for timeout even if already
updated some data
} GDALRasterIOHint;
class GDALRasterIOContext {
public:
GDALRasterIOContext() {
eStatus = GRS_Continue;
pszError = NULL;
}
public:
// Continue raster io, update pData buffer with new data, nUpdate??? =
bounding box of all updated blocks
// return CE_None if updated with new data
// return CE_Again on timeout
// return CE_Failure on error
virtual CPLErr RasterIO(void *pData, int nTimeoutMilliseconds = -1,
int nHint = 0);
public:
GDALRasterIOStatus eStatus;
char *pszError; // if eStatus == GRS_Error this should contain
human readable error message, NULL otherwise
int nUpdateXOff;
int nUpdateYOff;
int nUpdateXSize;
int nUpdateYSize;
};
class GDALDataset {
...
public:
virtual GDALRasterIOContext *StartRasterIO(
GDALRWFlag eRWFlag, int nXOff, int nYOff, int nXSize, int nYSize,
int nBufXSize, int nBufYSize, GDALDataType eBufType,
int nBandCount, int *panBandMap, int nPixelSpace, int
nLineSpace, int nBandSpace
);
virtual void EndRasterIO(GDALAsyncRasterIOContext *poContext);
};
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