We have a QProcess that runs a bash script. The script finishes properly and produces expected output, but the finished signal takes a very long time (minutes) afterward to emit. Basically, our script is generating an encrypted tarball from a list of files fed as an argument. The final bundle is sitting there on disk, intact, but Process takes a very long time to return. This is preventing our UI from moving on to the next task, because we need to ensure the script has run to completion programatically, instead of through inspection. We're not doing anything other than
connect(myProcess, SIGNAL(finished()), mySlot, SLOT(tidyUp()));
myProcess.start();
We can monitor the size of the file with Qt, and we have an estimate of its final size based on the file list we feed the script, but the script hangs around for a very long time after the file has reached its estimated size. We've inserted sync statements, but that doesn't seem to have any effect. When the script is run on the command line, the file grows, and the script stops as soon as it reaches its final size.
Why is QProcess not sending it's finished signal immediately after the script completes?
We would very much like to attach a progress bar indicating percentage of file size produced, or give some other indication of progress, but we're stumped by this behavior. We've tried using both a worker thread moved to a QThread, and running the QProcess directly in a busy loop, calling processEvents(), to no avail.
Turns out this was a problem with the commands I had in my pipe. GPG plunks out the file fairly quickly (quite variable timing, though) but then often spends quite a lot of time idling/working after the file itself has reached its final size. I'm not sure what it's doing, or why it only does on some runs of the same content, but eventually it finishes, the script completes, and I get my finished() signal delivered. I may have to put a more elaborate progress bar in place that switches to busy wait if the file size hasn't changed for a while, but it appears that Qt is working as expected here after all.