On quarta-feira, 20 de março de 2013 23.00.19, Guido Seifert wrote: > Hi, > I have here a strange problem. Probably not 100% ontopic for this list. But > it is a Qt program. :-) > > My problem: I have three programs, which exchange data with a fourth program > via tcp and udp. On my i7 and i5 with four cores it runs perfectly. It also > runs perfectly on my partner's machines. Now I gave it to a few testers... > and it was pure disaster. Bugs I have never seen before. From the > description it seems to be some kind of deadlock. The main program just > freezes. None of the four programs are multithreaded. At least not > directly. The programs use the Qt network classes. Since I don't have an > unlimited pool of hardware I tried to run my program in a Windows 7 and > Windows 8 installation in a VirtualBox environment. And strangely I could > see exactly the reported behaviour. But only when I gave the virtual > machine < 4 cores. As soon as I switched the virtual machine to four or > more cores everything worked perfectly again. Slow and jerky, but generally > as expected. > > This behaviour is not 100% consitent. There is a tester with an i7 machine > and four cores, who sees the same blocking behaviour. > > I am a little at a loss here. Anyone of you seen something similar? Any > ideas what the problem could be?
Hi Guido It's very hard to make a guess with so little information. If the number of cores appears to affect the outcome of the execution, it usually means a threading problem (where "threading" here can be across processes too). If you increase the number of cores and it stops working, it's usually a race condition. Since decreasing the number of cores makes it work, I would guess it's a priority inversion problem: you have too many tasks doing a lot of work that are hogging the available cores, but depend on data from other tasks. Those other tasks aren't getting CPU time. -- Thiago Macieira - thiago.macieira (AT) intel.com Software Architect - Intel Open Source Technology Center
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
