Detect whether there is a qws server running

Question

In order to properly launch a little Qt app on an embedded system, I need a reliable way to find out whether a Qt QWS server is already running.

Otherwise I'd need to supply the -qwsoption to the app to run the server itself. Is there a way of doing it?

Answer 1

The only quick workaround coming to mind is this:

ps aux | grep "\-qws"

and check if that returns anything. Other than that, I think you should obsolete qws in your project as it is a relatively old and broken concept with today's standards.

Answer 2

Here is the solution I settled for:

The QWS server uses to socket to talk to its clients. I test for the existence of this socket.

I also test whether the server actually has the socked open in order to avoid falling for orphaned sockets left over after a QWS server crash. This is done using lsof (list open files) on the socket. If the server is running, the list will not be empty and lsof will return true. If the server is not running, lsof will return false.

On my system the socket was located in /tmp/qtembedded-0/QtEmbedded-0

So here is the bash code:

QWSSOCK=/tmp/qtembedded-0/QtEmbedded-0

if [ ! -S $QWSSOCK ] ; then
    echo "No socket $QWSSOCK"
    QWSOPT=-qws
elif lsof $QWSSOCK ; then
    echo "Server running on $QWSSOCK"
    QWSOPT=
else
    echo "No server on $QWSSOCK"
    QWSOPT=-qws
fi

After this I can run my Qt app using the $QWSOPT variable:

app $QWSOPT