QThread internal error while waiting for adopted threads: 87

Under Windows I get this message from time to time:

QThread internal error while waiting for adopted threads: 87

This message comes from Qt and is printed by qWarning() method. I found where and why this happens.

This happens in method qt_adopted_thread_watcher_function in files corelib/thread/qthread_win.cpp.

The reason is that, when size of array qt_adopted_thread_handles is a multiple of MAXIMUM_WAIT_OBJECTS (which is 64), the last call to WaitForMultipleObjects in do-while loop contains count == 0. But this is not allowed according to MSDN and call fails with GetLastError() == ERROR_INVALID_PARAMETER, which is 87. It does no harm to a program, but warnings are annoying.

I made a test to reproduce the problem. See attached file. 2 fixes are possible:

Fix 1:
int loops = (handlesCopy.count() / MAXIMUM_WAIT_OBJECTS), offset, count;
if ( (handlesCopy.count() % MAXIMUM_WAIT_OBJECTS) > 0 )
{
loops++
}

Fix 2:
count = qMin(handlesCopy.count() - offset, MAXIMUM_WAIT_OBJECTS);
if ( count > 0 )
{
ret = WaitForMultipleObjects(count, handlesCopy.constData() + offset, false, 100);
}