alexei-zaripov

C/C++ performance pitfall: int8_t, aliasing and the ways out

When I was working on a generic port of Google's hashmap to C, I wrote a function that (ignoring irrelevant parts) looked like this:

typedef struct {
    uint8_t *bytes;
    size_t len;
} bytebuf;

Verdagon

# Does Python have data races?
#
# As we've seen, Java can have data races, according to
# https://docs.oracle.com/javase/specs/jls/se8/html/jls-17.html
# It says an example of a data race is when:
# - there is a write in one thread,
# - a read of the same variable by another thread,
# - and the write and read are not ordered by synchronization.
#
# This program attempts to cause a data race in Python.

thales17

Download and install msys2 64bit

• Download msys2 64bit from here: https://www.msys2.org/

Update msys2

• Update msys2 64bit after install by running pacman -Syu if pacman needs to be updated you might have to close and reopen the terminal and run pacman -Syu again

Install build tools

• pacman -S git mingw-w64-x86_64-toolchain mingw64/mingw-w64-x86_64-SDL2 mingw64/mingw-w64-x86_64-SDL2_mixer mingw64/mingw-w64-x86_64-SDL2_image mingw64/mingw-w64-x86_64-SDL2_ttf mingw64/mingw-w64-x86_64-SDL2_net mingw64/mingw-w64-x86_64-cmake make

Compile Hello World

fay59

Here's a list of mildly interesting things about the C language that I learned mostly by consuming Clang's ASTs. Although surprises are getting sparser, I might continue to update this document over time.

There are many more mildly interesting features of C++, but the language is literally known for being weird, whereas C is usually considered smaller and simpler, so this is (almost) only about C.

1. Combined type and variable/field declaration, inside a struct scope [https://godbolt.org/g/Rh94Go]

struct foo {
   struct bar {
 int x;

totherik

Per https://code.google.com/p/v8/codesearch#v8/trunk/src/runtime.cc


%CreateSymbol
%CreatePrivateSymbol
%CreateGlobalPrivateSymbol
%NewSymbolWrapper
%SymbolDescription
%SymbolRegistry
%SymbolIsPrivate

rxaviers

People

:bowtie:	😄 :smile:	😆 :laughing:
😊 :blush:	😃 :smiley:	☺️ :relaxed:
😏 :smirk:	😍 :heart_eyes:	😘 :kissing_heart:
😚 :kissing_closed_eyes:	😳 :flushed:	😌 :relieved:
😆 :satisfied:	😁 :grin:	😉 :wink:
😜 :stuck_out_tongue_winking_eye:	😝 :stuck_out_tongue_closed_eyes:	😀 :grinning:
😗 :kissing:	😙 :kissing_smiling_eyes:	😛 :stuck_out_tongue:

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD