[BZ#770982] meld fails to properly render over X11 forward tunnel with as latency increases to remote Xming Xserver

Submitted by James

Description

Description of problem: meld fails to properly render over X11 forward tunnel with as latency increases to remote Xming Xserver. In general seems 16-22ms latency is enough.

Version-Release number of selected component (if applicable): meld-3.11.0-1.el7.2.noarch (also tested meld-3.16.2/bin/meld) Both Xming 6.9.0.31 & Xming 7.5.0.62 (both tested) Windows 7 & Windows 10 (both tested)

How reproducible: Very with latency connection or by inflicting latency

Steps to Reproduce:

Need RHEL 7 system with meld, ssh, xauth

Need Windows system (vm works) with Xming & putty (w/ X11 Forwarding). Windows 7 & Windows 10 both seem to have issue

Start meld - should render fine. Then close
meld /etc/passwd /etc/group

Now add some artificial latency (start with ~12ms)
tc qdisc replace dev eth0 root netem delay 12ms

Repeat step 3 & 4 an increase latency until meld fails to render and get just spinner. 16ms works for me, but another user too 22ms.

Actual results: Once latency increases meld fails to render on the Windows Xming properly. If do get the text, it will fail to provide visual color difference. Once you replace with 0ms things work.

Expected results: meld should be able to handle this reasonable latency, as issue initially reported by user forwarding X11 from USA to UK.

Additional info:

From windows cmd.exe you can use 'ping -t ' to see the latency changes take effect from the tc command.

Issue was originally reported to EPEL: https://bugzilla.redhat.com/show_bug.cgi?id=1370627