[Digikam-devel] [Bug 163602] Race condition during image download from Camera/ USB device: image corruption and/or loss (patch attached)

[Roger Larsson]

http://bugs.kde.org/show_bug.cgi?id=163602





--- Comment #5 from Roger Larsson <roger larsson e-gatan se>  2008-08-19 22:10:14 ---
I have reviewed the patch/change.

The race was between 'CameraCommand::gp_download' and
'CameraEvent::gp_downloaded'

Normally the messages/events arrive
'CameraCommand::gp_download'
   emits a gp_downloaded("file-PID")
'CameraEvent::gp_downloaded(temp)'

'CameraCommand::gp_download'
   emits a gp_downloaded("file-PID")
'CameraEvent::gp_downloaded(temp)'

And the temp parameter will be the same but it wont matter
since processing keeps the sequence.

If the message queue becomes
'CameraCommand::gp_download'
   emits a gp_downloaded("file-PID")
'CameraCommand::gp_download'
   emits a gp_downloaded("file-PID")
'CameraEvent::gp_downloaded(temp)'
'CameraEvent::gp_downloaded(temp)'

But in this case the second gp_download will overwrite the same file as used
earlier. Final processing, 'gp_downloaded', will be done with the wrong file
contents. And the last 'gp_downloaded' will fail since the file has either been
renamed or removed.
=> this matches the observed behavior.

The patch looks OK to me.


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