On 11/07/2016 07:22 PM, william.croc...@analog.com wrote:
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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/libQt5Core.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/libQt5Core.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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