Load Algorithms, improve selection speed, particularly for Nexus files

[NickDraper]

This ticket is blocked by :

• TRAC7352

This ticket is blocks : TRAC7065

If we pass around an open file pointer to the FileCheck methods nexus loaders (and others) can use the open pointer to perform their tests, rather than each open the file themselves. This should be much faster.

Source email from James Lord:

If I have a script/algorithm to process a batch of runs and I write it in a generic 
way using Load(), it takes about twice as long as using the correct specific load 
routine such as LoadMuonNexus(). I suspect Load() is first opening the file to 
inspect the format then closing it and passing the filename onto the format-specific 
version, which opens it again and ignores any cached data.

I've checked with files from the local disk and those from a network drive 
(//hifi/data) and while the local files load faster there is still the same 
improvement to be had by switching to LoadMuonNexus().

In this case I am (intentionally) loading all spectra, and the logs, from muon 
Nexus files of about 750kbytes each (on disk).

Is there any improvement to be made such as caching the file or being able to 
"hint" to Load() that the next file in a sequence is almost certainly going to be 
the same file format as the last one it just loaded?

James Lord.
(Mantid 2.5.3 at present, Windows 7)

[NickDraper]

This issue was originally trac ticket 7263

[NickDraper]

http://trac.mantidproject.org/mantid/raw-attachment/ticket/7263/load.py
(uploaded by @martyngigg on 2013-07-05T12:58:05)

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