Review Request 118686: libkdeedu / parley : fix Bug 240552 - Second parley process cancels out changes in language file when closing

[Andreas Xavier]

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https://git.reviewboard.kde.org/r/118686/
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(Updated June 18, 2014, 10:06 a.m.)


Review request for KDE Edu.


Changes
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Adds a comment to clarify the use of m_autosave.

I just noticed it works correctly when you open 2 parley instances and then open a file twice, as I originally tested it.

However, this time I also turned on automatically load last loaded vocdoc, the 2nd parley instance just crashes.  

If you commit it, I will submit these 2 bugs: 
  1. Second Parley instance crashes on autoload of same file. 
  2: Feature request steal lock. 


Bugs: 240552
    http://bugs.kde.org/show_bug.cgi?id=240552


Repository: libkdeedu


Description
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Implement a lock on the language file.

The problem: When 2 or more instances of parley open that same language file,
the last instance to exit overwrites all of the previous changes.

This patch implements unit-tests that demonstrate the problem, and file locking
on the language file to fix the problem.

The unit tests are straight forward with different combinations of open, editing and saving
language files. The conditions that I anticipated would replicate the problem.

As a solution this patch uses KAutoSaveFile to implement file locking.  m_autosave replaces m_url to track the file.
Second and subsequent instances of KEduVocDocument can't get a lock for the file.  From a programmer perspective
it returns FileCannotWrite when file access fails.  From a user perspective it says that it
can't read collection from <file name>.

I added KEduVocDocument::close() to the public interface for symmetry with open().  It is not necessary and if interface changes are inconvenient at this time, it can be removed.  Destroying the KEduVocDocument, changing the Url with setUrl or saveAs, or opening another file all close the currently open file and eliminate the lock.

One foreseeable problem is that the current parley interface doesn't offer a way to remove the lock if parley crashes.
The vocabulary file would have to be renamed by hand.  However, this is an improvement from data loss to data inaccessible.
The obvious solution is to add a value to the error enumeration that means the file is locked, and then offer the user to option to steal the lock.  That would require changes to the KEduVocDocument interface. 


Diffs (updated)
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  keduvocdocument/keduvoccontainer.cpp ded5410 
  keduvocdocument/keduvocdocument.h dfd45c3 
  keduvocdocument/keduvocdocument.cpp b73fc69 
  keduvocdocument/keduvockvtml2writer.cpp 859ab8b 
  keduvocdocument/tests/CMakeLists.txt f05b787 
  keduvocdocument/tests/keduvocdocumentfilelockingtest.cpp PRE-CREATION 
  keduvocdocument/tests/keduvocdocumentvalidatortest.cpp 834564c 

Diff: https://git.reviewboard.kde.org/r/118686/diff/


Testing
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1. Unit tests
2. Opened 2 instances of parley and verified that only one could use the file and then after exiting
  that the other could then use the file and then that both successive sets of results had been saved. 


Thanks,

Andreas Xavier

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