[Qt-interest] Qt 4.6.3 QApplication constructor (Windows 7) EXTREMELY slow?

[Paul Miller]

Just spent the last 2 days tracking down an intermittent performance 
problem with QApplication construction.

Symptoms:
1. on my machine, everything was fast - QCoreApplication would 
initialize consistently in about 60ms (release mode)

2. on 2 tester machines, and on a completely clean Windows 7 x64 VM, the 
same app would start up sporadically quickly, but then every now and 
then (every 5-10 runs) would take about 16 seconds longer on the 2 test 
machines, and about 10 seconds longer on the VM.

3. after awhile, the test app would ALWAYS take 10 seconds longer than 
usual to start up on the VM (as I said none of this happened on my dev 
machine so the VM was all I had available to test with). Results were 
consistent with 2 off-site test machines.

I switched back to 4.5.3 Qt dlls and everything started working properly 
on all machines, and QApplication init time went down to about ~1ms.

Note all of the test machines were fairly clean, with no standard Qt 
installation and pretty stock runtimes/patches installed. Basically just 
test app + required Qt dlls in a directory. Development machine was 
loaded with Visual Studio, various runtimes, various Qt installs, etc. etc.

Anyone seen anything like this? Is Qt 4.6.3 doing something radically 
different during app startup now?