Daniel NicolettiBrazil, São Paulo http://dantti.wordpress.com 58 Posts
Cutelyst the C++/Qt Web Framework and ASql the ASync SQL library for Qt applications got new versions.
Thanks to the work on ASql Cutelyst got some significant performance improvements on async requests, as well as a new class called ASync, which automatically detaches the current request from the processing chain, and attaches later on when it goes out of scope.
With the ASync class you capture it on your ASql lambda and once the query result arrives and the lambda is freed and the ASync object gets out of scope and continues the processing action chain.
KDAB's fix on a 10 year old bug raised my attention back to a note on QTcpSocket documentation:
Note: TCP sockets cannot be opened in QIODevice::Unbuffered mode.
Which is actually wrong, according to the source code, Cutelyst has been using buffered mode since always due that, so hopefully this new version will be a bit faster and consume less memory, it's important to notice that once the Kernel tells it's going to block QTcpSocket writes get buffered anyway.
Now talking about ASql you might notice the jump on release versions, this is because I've been experimenting some changes and didn't want to write a post at each new feature.
ASql is now at the closest API I'd like it to be, unfortunately one of my goals that would be to be able to handle it's AResult object to Grantlee/Cutelee and be able to iterate over it's records just once, but the call QVariant::canConvert with QVariantList must succeed and the class be able to be casted to QAssociativeIterable or QSequentialIterable, which I didn't managed to get it working in a way I like.
But AResult has hash() and hashes() methods that convert the data to a format that can be used in templating.
On the plus side I added iterators (if you have experience with iterators please review my code as this was the first time I wrote this kind of code) that also work on for ranged loops, and they also have faster type conversion methods, instead converting the data to a QVariant type, and them using QVariant to get the data out of it, one can just call toInt() which will get the int straight from the result set without checking each time if it's an int.
Added AMigrations which is an awesome database maintenance class that is both simple and helpful to maintain database schemas.
- ACache class to cache special queries
- Support for data inside QJsonValue
- Single Row mode (the lambda get's called once per result)
- Prepared Queries
- Scoped Transaction class
- Notifications - this is my favorite PostgreSQL feature, it's hard to image some other big databases lack such an useful feature.
Oh, and Cutelyst results on TechEmpower already got better thanks to ASql, hoping to see even better results when I update the tests to 2.13 that has Unbuffered and faster async handlying.
Cutelyst a Qt web framework got a new version, this version has one important fix for async apps using FastCGI or HTTP2, also fixes for SO_REUSEPORT, and as a new feature is has support for listen queue backlog on UNIX, sadly QTcpServer doesn't support both of these (I need to find time to write some patches...).
Cutelyst is available for many Linux distributions but doesn't for Debian/Kubuntu, so I'm also adding the CPack deb built will all but uWSGI support for 20.04 amd64.
When developing Qt applications be it Desktop, Mobile or Web that need to talk directly with a database the use of QtSql is usually the best choice, it has many database drivers, comes ready on their installer, but has a blocking API, which means a query will block you GUI thread.
My Cutelyst Web projects also used QtSql, and for low traffic this isn't a big issue because you are not freezing users GUI, but you are freezing the request queue instead.
One of the Cutelyst apps I developed this year has a very high traffic, and a side effect of blocking came in play, I've about 3k TVs connected via websockets, once a TV connects it does an authentication query, it takes ~17ms, now when there is an event PostgreSQL notifies the application which does some 20 other queries a little more expensive (~30ms) and send them to the TVs, this event also blocks the Cutelyst process.
Every TV does a websocket ping each 15 seconds to check if the connection is stalled, when that event happens plus some latency added 15s timeout and the TV disconnect, this of course happens with lots of TVs, so 1k TVs reconnecting will take around 17 seconds, this means new TVs disconnecting and the snow ball is done, system only recovers if I increase the DB hardware on AWS.
How can async fix this, you might be wondering, well the problem is that the 15s timeout happened to do a DOS on my own system, I can increase the value but when there are 10k TVs this will still be a problem, there are of course other ways to deal with this, but if the SQL query doesn't block the Cutelyst process it will be able to timely reply the Websocket's pongs.
ASql only supports PostgreSQL at time (PR are welcome), and depends on QtCore and libpq (PostgreSQL library), it can be used on Desktop apps and is 100% async from connection to queries, there's even a class to help with DB versioning and migration.
Check it out: https://github.com/cutelyst/asql
Cutelyst the web framework based on Qt and SimpleMail the SMTP library got another update.
The current scenario has made me a lot less productive, after all 4 kids at home all the time it's really hard to concentrate. Still many fixes and a few features have landed both.
Simple mail had issues building on Windows, and also got some docs fixes.
Cutelyst got some Session parameters available on config, an WebSocket improvement to avoid setting a null body to skip RenderView processing, and a new view called Cutelee.
This year I got a big project, one that is pushing scalability on Cutelyst further, but it also requires that things progresses faster, and this means Grantlee was starting to become an issue. A while ago it's maintainer proposed to move it's code to KDE, got my hopes high, but that got postponed to Qt6, I couldn't wait for that and I also had an years old Pull Request waiting there, making in fact Cutelyst pages less safer as an escaping code wasn't escaping one special character. A Cutelyst contributor also had patches pending there, I tried my best to avoid this, the author is a great programmer, did an awesome job but we needed something that can move a little faster.
Cutelee was born, and already have many commits, it also got some performance improvements, like not converting QDate(Time) to an string and converting back to use the :date "yy/dd" formater, another important change was that it can inject filters without the hassle of creating a Qt Plugin, putting it into the right and error prone directory hierarchy, %with% tag also supports the new Django syntax, and I hope we can keep improving it at a faster rate.
I didn't do a new release of it yet, as some installation issues raised at Grantlee weren't fixed yet on Cutelee.
Cutelyst the C++/Qt Web framework and SimpleMailQt just got new releases.
Cutelyst received many important bugfixes and if you are compiling it with View::Email it also requires SimpleMail 2, the latter got an Async API which is on production for a few months, allowing for a non-blocking send mail experience.
Check them out!