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https://launchpad.net/bugs/1055441
* lp:~mvo/software-center/downloader-fix-race839462-again:
  - fix a race condition in the SimpleFileDownloader when the file
    is downloaded but the signal did not get delivered yet by the
    gtk event loop (LP: #1055441)

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Lines of Context:
softwarecenter/utils.py
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        f.query_info_async(Gio.FILE_ATTRIBUTE_STANDARD_SIZE, 0, 0,
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                           self._cancellable,
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                           self._check_url_reachable_and_then_download_cb,
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                           None)
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    def _check_url_reachable_and_then_download_cb(self, f, result,
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                                                  user_data=None):
 
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                           url)
 
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    def _ensure_correct_url(self, want_url):
 
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        """This function will ensure that the url we requested to download
 
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           earlier matches that is now downloaded.
 
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        """
 
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        # this function is needed as there is a rance condition when the
 
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        # operation is finished but the signal is not delivered yet (its
 
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        # still in the gtk event loop). in this case there is nothing to
 
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        # self._cancel but self.url/self.dest_file_path will still point to
 
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        # the wrong file
 
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        if self.url != want_url:
 
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            self.LOG.warn("url changed from '%s' to '%s'" % (
 
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                    want_url, self.url))
 
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            return False
 
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        return True
 
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    def _check_url_reachable_and_then_download_cb(self, f, result, want_url):
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        self.LOG.debug("_check_url_reachable_and_then_download_cb: %s" % f)
 
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        if not self._ensure_correct_url(want_url):
 
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            return
 
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        # normal operation
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        try:
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            info = f.query_info_finish(result)
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            etag = info.get_etag()
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                                                        etag))
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            # url is reachable, now download the file
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            f.load_contents_async(
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                self._cancellable, self._file_download_complete_cb, None)
 
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                self._cancellable, self._file_download_complete_cb, want_url)
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        except GObject.GError as e:
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            self.LOG.debug("file *not* reachable %s" % self.url)
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            self.emit('file-url-reachable', False)
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            self.emit('error', GObject.GError, e)
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        del f
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    def _file_download_complete_cb(self, f, result, path=None):
 
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    def _file_download_complete_cb(self, f, result, want_url):
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        self.LOG.debug("file download completed %s" % self.dest_file_path)
 
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        if not self._ensure_correct_url(want_url):
 
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            return
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        # The result from the download is actually a tuple with three
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        # elements (content, size, etag?)
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        # The first element is the actual content so let's grab that