* Talks

Slides and example code from two technical presentations given in 2020.

Slides use [[https://orgmode.org/][org-mode,]] and were presented in Emacs with [[https://github.com/rlister/org-present][org-present]].

** Concurrency (June 2020)

Introduction to concurrency.

*** Slides
- Sequential vs. concurrent execution, I/O latency, interrupts, and cooperative vs. preemptive scheduling
- Concurrency vs. parallelism, processes vs. threads, and language runtimes (C, JavaScript event loop, Go scheduler)
- Shared memory synchronization vs. message passing, backpressure, and distributed data races

*** Examples
- temperatures: concurrent HTTP requests fetching city temperatures from OpenWeatherMap.
- mutex: data race demonstration and mutual exclusion on a shared bank account balance (~go run -race ./main.go~).
- csp: pipeline of goroutines and channels reading a CSV of zip codes, querying weather data with a concurrency limiter, and displaying a live top-ten leaderboard.

To run the examples:
#+begin_src shell
# Mutex example (with and without race detector):
cd concurrency/cmd/mutex
go run ./main.go
go run -race ./main.go

# Weather examples (require an OpenWeatherMap API key):
export OPEN_WEATHER_MAP_API_KEY="..."
cd concurrency/cmd/temperatures && go run .
cd concurrency/cmd/csp && go run .
#+end_src

** x86-64 Assembly (November 2020)

A brief tour of x86-64 assembly on Linux.

** Slides
- Compilation pipeline, ISAs, CPU registers, and Linux system calls
- Instructions, addressing modes, control flow, and memory safety
- Virtual memory, the stack, function prologues/epilogues, and the System V AMD64 ABI calling convention

** Examples
- exit: minimal program invoking the ~exit~ system call.
- math: basic arithmetic instructions (~mov~, ~add~, ~sub~, ~mul~, ~div~), inspected via exit status.
- control-flow: loops, comparisons (~cmp~), and conditional/unconditional jumps (~je~, ~jmp~).
- hello-world: writing a string from the ~.data~ section to stdout with the ~write~ system call.
- safety: out-of-bounds memory overwrite across adjacent ~.data~ buffers.
- stack: pushing bytes onto the stack and printing from ~%rsp~.
- func: function call, stack frame setup (~%rbp~ / ~%rsp~), and return.

To run the examples:
#+begin_src shell
as exit.s -o exit.o
ld exit.o -o exit
./exit
echo $?
#+end_src