InfoComicsView constructor is the only function that connects to
FlowView's currentCoverChanged signal. Neither of the slots connected to
this signal handles the argument value index==-1. So when FlowView emits
this signal with index==-1, YACReaderLibrary crashes. Returning early
from either ComicsView::updateInfoForIndex() or
InfoComicsView::setCurrentIndex() when index==-1 is not sufficient - the
crash happens in the other slot then. Let us skip emitting the signal in
FlowView if index==-1 rather than return early from both slots.
Steps to reproduce 1:
1. Launch YACReaderLibrary version that matches the version of the
default library database. Alternatively, select a compatible library
after starting the application.
2. If InfoComicsView is not active, switch to it.
3. (optional) Switch to another comics view out of InfoComicsView.
4. Quit YACReaderLibrary. The application crashes during exit - after
the "YACReaderLibrary closed with exit code : 0" message is printed.
Steps to reproduce 2:
1. Launch a YACReaderLibrary version newer than the version of the
default library database.
2. Click the "No" button in the "Update needed" dialog that pops up.
3. Change between comics views until InfoComicsView becomes active. If
this view was active at the beginning, switch through all the views to
get back to it. At this point YACReaderLibrary crashes.
This way we can tell the app that a folder contains mangas so the user doesn't have to constantly set comics as manga when new issues are added. And it should be easier to set all the content in a folder as manga from the folder tree.
List initialization ended using movable constructors which surprisingly caused data troubles in release mode, at least in VC2019 compiler. The tree being messed up caused crashes while SQL was generated.
I have no explanation for it.
When setting ports, temporary or for good, we need to go via the config
files and not QTcpServer or we get undefined behavior. To support temp
ports, we need to back up the fixed port in the settings.
In a later commit WorkerThread should also replace classes similar to
ImageLoader: PageLoader, ImageLoaderGL and ImageLoaderByteArrayGL.
Bugs fixed:
1. Eliminated a data race between ImageLoader::run() and
ComicFlow::updateImageData()->ImageLoader::result(). Specifically when
ImageLoader::busy() returns false, then ImageLoader::run() sets
ImageLoader::working to true, loads the image and starts assigning it to
ImageLoader::img, while ImageLoader::result() is accessed without
locking from updateImageData().
Making ImageLoader::working atomic is clearly insufficient to eliminate
this data race. The fix is to set 'working' to true immediately and
synchronously as soon as a new task is assigned to the worker.
2. Replaced thread termination with graceful thread exit. ComicFlow
destructor called QThread::terminate(), using which is discouraged by Qt
documentation. The application exited without errors in Release mode.
In Debug mode, however, it received the SIG32 signal on exit and printed
the following warning - "QWaitCondition: mutex destroy failure:
Device or resource busy".
The loop in WorkerThread::run() is no longer endless. The worker thread
properly ends and is joined in WorkerThread destructor.
Design decisions:
1. WorkerThread could emit a signal when it completes a task.
Thus updateTimer could be removed from ComicFlow and GoToFlow. However,
there is no obvious way to use this new signal in the two GL classes.
Also I don't know whether updateTimer is just an inefficient polling
substitute for notification or an intentional animation mechanism.
2. The index variable is no longer stored in the worker class, but in
ComicFlow directly. Thing is, this data member was never actually
accessed by the worker, but ComicFlow went so far as to lock worker's
mutex to "protect" access to the index.
3. The common ImageLoader implementation turned out to be very general.
So I converted it into the WorkerThread class template that is not
restricted to producing QImage results and can be reused elsewhere.
4. I used standard classes (such as std::thread) instead of their Qt
equivalents (e.g. QThread) because they are more thoroughly documented.
The standard classes should also be more efficient as they were more
carefully designed and provide much fewer unnecessary features.
5. Release-Acquire ordering is safe for the WorkerThread::working
use case and is more efficient than the std::atomic-default
Sequentially-consistent ordering.
6. condition.notify_one() is called while the mutex is unlocked
to improve performance. This is safe in both cases:
a) if the worker thread exits due to a spurious wakeup just before
the condition.notify_one() call in WorkerThread destructor, so much the
better;
b) if a spurious wakeup lets the worker thread finish the task and
start waiting on the condition again just before the
condition.notify_one() call in WorkerThread::performTask(), the second
waking will be ignored by the worker thread as 'working' and 'abort'
will be false then.
