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  1. Qt
  2. QTBUG-24898

QFileSystemWatcher (inotify) and editors that rename files

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      Here is some strace output while using a file watcher.

      First, I touch the file.

      poll([{fd=3, events=POLLIN}, {fd=5, events=POLLIN}], 2, -1) = 1 ([{fd=5, revents=POLLIN}])
ioctl(5, FIONREAD, [16])                = 0
read(5, "\1\0\0\0\4\0\0\0\0\0\0\0\0\0\0\0", 16) = 16
write(2, "\"tst.cpp\" \n", 11"tst.cpp" 
)          = 11

      Then I use an editor (vi, gedit, probably most others) to save the file.

      poll([{fd=3, events=POLLIN}, {fd=5, events=POLLIN}], 2, -1) = 1 ([{fd=5, revents=POLLIN}])
ioctl(5, FIONREAD, [48])                = 0
read(5, "\1\0\0\0\4\0\0\0\0\0\0\0\0\0\0\0\1\0\0\0\0\4\0\0\0\0\0\0\0\0\0\0"..., 48) = 48
inotify_rm_watch(5, 1)                  = -1 EINVAL (Invalid argument)
write(2, "\"tst.cpp\" \n", 11"tst.cpp" 
)          = 11

      The same thing happens when I do "mv file tst.cpp". This is the 'atomic rename' pattern used in most editors when saving file contents.

      It seems QFileSystemWatcher stops watching the file in this case. It does fire it's signal one last time so a workaround is to continuously re-add the file:

      void MyObject::fileChanged(const QString &path)
{
    watcher->addPath(path); // in case it was saved using 'atomic rename'
    ...
}

      Shouldn't QFileSystemWatcher just detect the 'atomic rename' case and continue to watch the file? If not, shouldn't the documentation warn users of the class about this problem?

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            thiago Thiago Macieira
            lramsay Lincoln Ramsay (closed Nokia identity) (Inactive)
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              Created:
              Updated:
              Resolved:

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