Restartable Parsing

You must design the file parser so that parsing can be efficiently restarted at discrete locations within the file. The goal is to give the display engine the best performance without it having to store a completely converted copy of a file.

To facilitate restartable parsing, the display engine incorporates a module, which is called the chunker, that essentially caches data from the parser. The chunker does not cache all the data, only the data that the display engine has most recently requested. However, it does cache state data for restartable locations in the file. This means that as long as the parser maintains its own internal data in a way that can be efficiently restarted, the display engine and the parser can work cooperatively to locate and restart processing at the cached locations.

The file parser is responsible for determining the best locations for restarting parsing. It does this by calling the SOPutBreak function. The chunker assumes that each break is a restartable location in the file. Before calling SOPutBreak, however, the file parser must save up-to-date data about the location so that it can quickly retrieve and begin processing the data at the location if requested to do so.

The display engine uses the VwStreamSeekFunc and VwStreamTellFunc functions to direct the file parser to a restartable location.

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