Отсутствие динамической аллокации в embedded мире

Когда мы разрабатываем под embedded, нам приходится сталкиваться с такими флагами компиляции как -nostdlib -fno-exceptions -fno-rtti. Во многих средах нет malloc/free (new/delete) и вообще нет встроенного выделения памяти. Использование «больших» стандартных контейнеров C++ (например, std::vector) нередко исключено В результате приходится решать задачу «ручного» управления памятью. Ниже рассмотрим два подхода:

https://habr.com/ru/articles/918122/

#C++ #embedded #placement_new #heap #backend

Currently trying to tackle the #RAM consumption issue I see in #swad by introducing thread-local #pools (using simple linked lists) for frequently created and destroyed #objects like event-handler entries, timers, maybe also the connections served by a specific server ... instead of allocating a new one, the pool is asked for one, and instead of (fully) destroying one, it's returned to that pool.

It's a shot in the dark and will actually enforce memory for these is (almost) never free'd, but I hope it will avoid #heap #fragmentation. We'll see how it's going 🙈

I just stress-tested the current dev state of #swad on #Linux. The first attempt failed miserably, got a lot of errors accepting a connection. Well, this lead to another little improvement, I added another static method to my logging interface that mimics #perror: Also print the description of the system errno. With that in place, I could see the issue was "too many open files". Checking #ulimit -n gave me 1024. Seriously? 🤯 On my #FreeBSD machine, as a regular user, it's 226755. Ok, bumped that up to 8192 and then the stress test ran through without issues.

On a side note, this also made creating new timers (using #timerfd on Linux) fail, which ultimately made swad crash. I have to redesign my timer interface so that creating a timer may explicitly fail and I can react on that, aborting whatever would need that timer.

Anyways, the same test gave somewhat acceptable results: throughput of roughly 3000 req/s, response times around 500ms. Not great, but okayish, and not directly comparable because this test ran in a #bhyve vm and the requests had to pass the virtual networking.

One major issue is still the #RAM consumption. The test left swad with a resident set of > 540 MiB. I have no idea what to do about that. 😞 The code makes heavy use of "allocated objects" (every connection object with metadata and buffers, every event handler registered, every timer, and so on), so, uses the #heap a lot, but according to #valgrind, correctly frees everything. Still the resident set just keeps growing. I guess it's the classic #fragmentation issue...

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Введение в память, мотивация виртуальной, отображение между физической и виртуальной

У нас имеется физическая память, она одна для всех программ. И представьте, что вот вы разрабатываете программу, пишете алгоритмы, верстаете интерфейсы, свои контейнеры, это и так в силу несовершенства языков и сложности задач является довольно нетривиальной задачей, а теперь, задумайтесь: если вам нужно будет параллельно анализировать и запоминать, как вашей же памятью могли воспользоваться другие программы, или даже как ваше приложение пользуется ей. Как же оно получилось?

https://habr.com/ru/articles/914016/

#виртуальная_память #concurrency #C++ #регистры #rip #call_stack #heap #операционные_системы

Llama's Paradox - Delving deep into Llama.cpp and exploiting Llama.cpp's Heap Maze, from Heap-Overflow to Remote-Code Execution.

CC: @retr0reg

https://retr0.blog/blog/llama-rpc-rce

#llama #exploitation #heap #rce

DDoSecrets publishes 410 GB of heap dumps, hacked from TeleMessage

https://micahflee.com/ddosecrets-publishes-410-gb-of-heap-dumps-hacked-from-telemessages-archive-server/

#HackerNews #DDoSecrets #TeleMessage #data #breach #heap #dumps #cybersecurity #hacking

priority_queueにおける比較関数の渡し方（c++）
https://qiita.com/yuta4895/items/3950262cbbaaf16ffc1f?utm_campaign=popular_items&utm_medium=feed&utm_source=popular_items

#qiita #C #Heap #データ構造 #競プロ #Compare

Sketchbook (3 pages)
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#heap #tree #branches #trees #drawing #contemporaryart #paper #log #mask #contemporarydrawing #artwork #art #smallscale #sketchbook #contemporarydrawing #watercolor #painting #contemporarypainting #ink #MichaelLilin #Lilin #landscape #color #text