[Interest] [PROGRESS] Long pause with 5.7

[william.crocker at analog.com]

On 11/08/2016 09:14 AM, Michael Sué wrote:
> Hi,
>
> it could be a timeout of the lock used in QSettings.
>

Thanks for chiming in.

I use QSettings EVERYWHERE (tightly scoped) because I am big on
putting everything back where the user left it
and this call to show() is the only place that freezes.

Also, I put print statements around the call to processEvents and
verified that it takes 5 secs, SOMETIMES.

Bill

> - Michael.
>
> -----Original Message-----
> From: Interest [mailto:interest-bounces+sue=sf.mpg.de at qt-project.org] On Behalf Of william.crocker at analog.com
> Sent: Tuesday, November 8, 2016 2:56 PM
> To: interest at qt-project.org
> Cc: Thiago Macieira <thiago.macieira at intel.com>
> Subject: Re: [Interest] [PROGRESS] Long pause with 5.7
>
> On 11/07/2016 07:22 PM, william.crocker at analog.com wrote:
>> This sender failed our fraud detection checks and may not be who they
>> appear to be. Learn about spoofing at http://aka.ms/LearnAboutSpoofing
>>
>>>>
>>>> I am porting my app to Qt 5.7
>>>> When I run it, it appears on the screen, but there is a long pause
>>>> (~10 secs.) before it is responsive.
>>>> I ran it with strace and there is a point where it makes 100K calls
>>>> to the poll() function, which accounts for the long pause.
>>>> I tried running it in a debugger, but the app does not exhibit the
>>>> pause in that context.
>>>
>>> Sounds like a threading race condition and running in the debugger
>>> changes the timing just enough.
>>>
>>
>> Gave the debugger another try. On some occasions, it would take the
>> long pause. (The pause is more like 5 seconds.) If I interrupt it,
>> this is the stack trace.
>> Note that it is in the call to show() which precedes my call to
>> exec().
>>
>> Bill
>>
>> #0  0x0000003b0a0df113 in poll () from /lib64/libc.so.6
>> #1  0x0000003b0bc449f9 in ?? () from /lib64/libglib-2.0.so.0
>> #2  0x0000003b0bc44e4c in g_main_context_iteration () from
>> /lib64/libglib-2.0.so.0
>> #3  0x00007ffff55b2740 in
>> QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
>>      from
>> /nobackup/whc/qt/5.7.0-shared-debug-64Bit-RH6-NoOpenGL/qtbase/lib/libQ
>> t5Core.so.5
>> #4  0x00007ffff5565229 in
>> QCoreApplication::processEvents(QFlags<QEventLoop::ProcessEventsFlag>, int) ()
>>      from
>> /nobackup/whc/qt/5.7.0-shared-debug-64Bit-RH6-NoOpenGL/qtbase/lib/libQ
>> t5Core.so.5
>> #5  0x000000000098c60b in MyProg::show (this=0x7fffffffb8d0) at
>> prog.cpp:562
>> #6  0x0000000000986551 in MyMain (argc=@0x7fffffffc15c: 1,
>> argv=0x7fffffffc2f8) at prog.cpp:151
>> #7  0x0000000000986ad9 in main (argc=1, argv=0x7fffffffc2f8) at
>> yoda.cpp:221
>>
>
> I did not notice the call to show() was a call *MY* show().
> My bad, but there is still something funny going on.
>
> Since the beginning of time I have been searching for the way to restore window positions and sizes when a user reenters my app. This is especially tricky under X windows with the separate client/server, various window managers and window decorations. Following is part of my solution.
>
> It appears that with Qt 5.7, SOMETIMES, my call to processEvents waits for the full 5 secs even though I do not believe there is anything to do.
> That is why my app is SOMETIMES unresponsive for 5 seconds when I start it up.
>
> void
> MyApp::show() {
>
>       QSize sz; QPoint pos;
>       {
>           QSettings settings;
>           sz = settings.value("MainWindowWSize",QSize(1200,700)).toSize();
>           pos = settings.value("MainWindowPos",QPoint(180,190)).toPoint();
>       }
>
>       if( sz.width() > 0 && sz.height() > 0 ) {
>           resize(sz);
>           move(pos);
>       }
>
>       BaseClass::show();
>       qApp->flush();
>
>       // It appears that with Qt 5.7, SOMETIMES, this call to processEvents waits
>       // for the full 5 secs though I do not believe there is anything to do.
>       qApp->processEvents(QEventLoop::ExcludeUserInputEvents,5000);
>
>       if( sz.width() > 0 && sz.height() > 0 ) {
>           resize(sz);
>           move(pos);
>       }
>
>       raise();
> }
>
>
>
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