Review Request 118458: Fix KDirWatch to act more reliably against various backends.

[Matthew Dawson]

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https://git.reviewboard.kde.org/r/118458/
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(Updated June 6, 2014, 3:33 p.m.)


Status
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This change has been marked as submitted.


Review request for KDE Frameworks.


Bugs: 329802
    https://bugs.kde.org/show_bug.cgi?id=329802


Repository: kcoreaddons


Description
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Fix KDirWatch to act more reliably against various backends.

 - When KDirWatch used a FAM backend, it wouldn't actually wait for the
necessary watches to be put in place before returning, allowing for a race
where an application may think a watch is in place when it really isn't.
This was easily seen using gamin and running the testDeleteAndRecreateFile
test.  Fix by delaying useFAM until the watch is in place by waiting until
the EndExist FAM event is received.  This adds ~100-200ms per watch with
gamin.
 - When a file is deleted and recreated, and scanEntry detects it, the dirty
signal would be emitted.  Fix to emit a deleted + created signal, as expected.
 - When a deleted signal was requested, other signals were dropped.  Due to
the above point, this would stop the created signal from being emitted.  Now,
all signals are emitted, even when a delete is detected.
 - When watching recreated files, the created signal could get lost as there
was a race between when the created signal would be generated and its signal
spy would be created.  Fix by making sure the spy is created before the signal
could be emitted.
 - Make sure the created signal isn't emitted twice with both FAM and the
polling timer.  This occurs as FAM doesn't fix up the fact the entry has been
created, and the poller thus assumes it needs to notify the world.  Fix by
having FAM not emit the event in this case.

BUG: 329802

Note that due to a bug in the FAM daemon (which doesn't exist in the gamin daemon), the testDeleteAndRecreateDir unit test fails as FAM doesn't detect the folder deletion.  This test previously passed due to the race condition outlined in bug 329802, which was fixed in this RR.  I've confirmed this is a bug in FAM using a minimal program talking directly to the daemon, and watching the strace output from FAM.  FAM doesn't detect when a folder it is watching directly is deleted.  It does detect when a folder inside a folder it is watching is deleted, however.
I think this should go in as is, as the unit test failing exposes the actual problem, instead of hiding behind a race when it doesn't really work.  If running against FAM is important, I can see about tracking down the issue.


Diffs
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  autotests/kdirwatch_unittest.cpp 4e638e089012276dc8b17b9d960732a161cc3be1 
  src/lib/io/kdirwatch.cpp cc6feec4d2b2598e50c853172bbc295a8c719bc2 
  src/lib/io/kdirwatch_p.h cf63c41745091cfedcf1b27c9e4aa77d3db6b31a 

Diff: https://git.reviewboard.kde.org/r/118458/diff/


Testing
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Unit tests all pass now with gamin.  Using FAM, one test fails as described above, but I've confirmed the daemon itself is causing the issue.


Thanks,

Matthew Dawson

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