Seastar VS Qt

I used glommio as the async executor (instead of something like tokio), and it is wonderful. For people wondering whether it's "good enough" or to use C++ and seastar (as I have thought about a lot before starting this project), take the leap of faith, it's fast - both in terms of run time and to code.

b) It's proven now e.g Seastar, Glommio that the fastest way to run a multi-threaded application is to have one instance with one thread pinned per CPU core. Then to have fibers/lightweight threads on top handling all of the asynchronous code. Your approach of lots of instances is the slowest so there will be a ton of unnecessary thread context-switching.

The most common example is DPDK [1]. It's a framework for building bespoke networking stacks that are usable from userspace, without involving the kernel.

You'll find DPDK mentioned a lot in the networking/HPC/data center literature. An example of a backend framework that uses DPDK is the seastar framework [2]. Also, I recently stumbled upon a paper for efficient RPC networks in data centers [3].

If you want to learn more, the p99 conference by ScyllaDB has tons of speakers talking about some interesting challenges.

[1] https://www.dpdk.org/.

[2] https://github.com/scylladb/seastar

[3] https://github.com/erpc-io/eRPC

I assume Tokio itself, see e.g monoio or glommio, but also Seastar for C++.

https://core.dpdk.org/supported/ lists supported nics. You're best just reading material from the dpdk website for figuring out roughly what it is. It is used for a lot of different goals. For most web C++ stuff it's mainly used because you can avoid round trips of data passing through the kernel and can reference network data without tons of copying. For an example check out the SeaStar framework, https://seastar.io/, which is under the hood of ScyllaDB.

As this is a Kafka sub, this may be a good opportunity to mention that Redpanda is based on the same framework (seastar) as Scylla. The idea of sharding work to CPU cores turns out to apply very well to the Kafka data model, too!

Seastar which is a thread per core runtime written by the Scylla devs thats used in both Redpanda and Scylla as the underlying runtime. https://github.com/scylladb/seastar

ScyllaDB is, ironically, maybe one of the worst examples the author could have come up with for "abstraction" in the article.

If folks aren't familiar with their work/internal tech, go check out some of their repos like Seastar. They have some of the most talented systems programmers on the planet writing thin veneers over kernel and hardware API's to squeeze every ounce out of performance.

https://github.com/scylladb/seastar

I know it's beside the point, but I just had to share because I thought that was funny

I’ve seen frameworks for c++ (https://seastar.io/) and rust (https://github.com/actix/actix) which support what you’re describing out of the box.

If you're interested in scaling and asynchronous programming in c++ I highly recommend you investigate the SeaStar application framework. You wouldn't build a web service with SeaStar, rather you would build the infrastructure that you would use to build the web service on top of. https://github.com/scylladb/seastar

Qt mono repo : .. you could check out all submodules and simply use CMake to exactly achieve this. A mono repo also means that if I only use qtbase and declarative, I would need to have all submodules in there? - No

For e.g. if you’re writing a framework, you need to interface with Cocoa on MacOS to draw windows, which only provides an Objective C or Swift interface. You can look at the Qt source code and see how they do it: https://github.com/qt/qtbase/tree/067b53864112c084587fa9a507eb4bde3d50a6e1/src/plugins/platforms/cocoa

That's because Qt 6 wholeheartedly converted to CMake for you. (At least it is better than qmake.) In order to support this Qt has this large battery of CMake files [1]. Qt is of course a clear outlier, but you can't expect the same level of support from every other library you want. My points about "anything exotic" still stand.

[1] https://github.com/qt/qtbase/tree/dev/cmake

What are you talking about? Qt has GTK theme support built-in: https://github.com/qt/qtbase/tree/dev/src/plugins/platformthemes/gtk3

This looks like the Qt bug solved by this commit: https://github.com/qt/qtbase/commit/acaabc9108dfe75530960cf8e3ec4f3602cd82e0

Yeah, I'm sure it's completely unheard of. Oh except that it took me all of a couple minutes to find an example of that exact thing in one of the largest, most commonly used C++ frameworks out there.

I don't see any connect in https://github.com/qt/qtbase/blob/dev/src/corelib/tools/qsharedpointer_impl.h, and QPointer isn't a QObject (though I don't know if the latter is actually necessary for signal-slots). One (unreliable) way to test is to see if a QPointer fails to be nulled out when the QObject is blocked by a QSignalBlocker. Alternatively I'd set a data breakpoint on a QPointer and try it out. But I don't have the time right now.