Error on multiple parallel requests

[jo-bru]

If more than four commands are sent in parallel, some commands will fail.

Example Error: Error: Command failed: xarm-commander -i 130.82.171.9 -v get_position

This error can be reproduced by calling more than four commands in parallel running for example the following:

Promise.all([
            sendCommand(['-i', IPaddress, '-v', 'get_version']),
            sendCommand(['-i', IPaddress, '-v', 'get_state']),
            sendCommand(['-i', IPaddress, '-v', 'get_state']),
            sendCommand(['-i', IPaddress, '-v', 'get_state']),
            sendCommand(['-i', IPaddress, '-v', 'get_position'])]);
    })

To understand this error, it should be investigated how many connections can be processed simultaneously by the CPLUS SDK.

[jo-bru]

This problem may be solved if a persistent connection is established (see #18).

[jo-bru]

This is not relevant anymore, as we use an other system architecture (gRPC instead of plain xarm-commander).