Network slowdown when using QtCreator



  • I've got a weird one for all you hardcore Qt nerds. I'm writing a TCP client/server application. I'm testing this on my MacBook Pro running OSX 10.10.4 and using Qt 5.5.0. I've got the MBP connected to a wifi router. There is also another MacBook connected to that router. The router itself is disconnected from the internet. Ping times from one computer to the other average around 9 msec.

    What I'm finding is that after a few debugging sessions, a strange wifi network slowdown occurs about every 10 seconds. The ping times will jump into the hundreds of milliseconds for a few pings and then drop back to 9 msec. I've tried pretty much everything such as buying a new router, updating OSX to 10.10.4, running the test in an big open field where there are no other wifi signals in the area, shutting down all network-related background apps, etc.
    There are two important observations here. First, once this network slowdown occurs, even though neither of my Qt apps are running, the slowdown continues to happen. Second, as soon as I quit QtCreator, the slowdown goes away. I can relaunch QtCreator and run a few more sessions before the problem crops up again.
    I have verified this by launching OSX's Activity Monitor tool. When this slowdown is happening, there is no network traffic at all. I've even verified this with Wireshark. What is happening is that about every 10 seconds, QtCreator jumps to the top of the CPU activity list and I can see this match up with the jump in ping times if I have ping running in a Terminal and Activity Monitor running next to it along with QtCreator.

    So, here's the $64k question: What's causing this and how do I fix it?


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