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Assets #9

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May 15, 2018
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Assets #9

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2ced718
Update repo URL
dbkaplun May 15, 2018
5986c3a
mv *.png assets/
dbkaplun May 15, 2018
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0 .load.png → assets/load.png
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0 .store.png → assets/store.png
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8 changes: 4 additions & 4 deletions readme.md
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Atom
====

[![Build Status](https://travis-ci.org/slide-rs/atom.svg?branch=master)](https://travis-ci.org/csherratt/atom)
[![Build Status](https://travis-ci.org/slide-rs/atom.svg?branch=master)](https://travis-ci.org/slide-rs/atom)
[![Atom](http://meritbadge.herokuapp.com/atom)](https://crates.io/crates/atom)

`Atom` is a simple abstraction around Rust's `AtomicPtr`. It provides a simple, wait-free way to exchange
data between threads safely. `Atom` is built around the principle that an atomic swap can be used to
safely emulate Rust's ownership.

![store](https://raw.githubusercontent.com/csherratt/atom/master/.store.png)
![store](https://raw.githubusercontent.com/slide-rs/atom/master/assets/store.png)

Using [`store`](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.store) to set a shared
atomic pointer is unsafe in rust (or any language) because the contents of the pointer can be overwritten at any
point in time causing the contents of the pointer to be lost. This can cause your system to leak memory, and
if you are expecting that memory to do something useful (like wake a sleeping thread), you are in trouble.

![load](https://raw.githubusercontent.com/csherratt/atom/master/.load.png)
![load](https://raw.githubusercontent.com/slide-rs/atom/master/assets/load.png)

Similarly, [`load`](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.store)
is unsafe since there is no guarantee that that pointer will live for even a cycle after you have read it. Another
thread may modify the pointer, or free it. For `load` to be safe you need to have some outside contract to preserve
the correct ownership semantics.

![swap](https://raw.githubusercontent.com/csherratt/atom/master/.swap.png)
![swap](https://raw.githubusercontent.com/slide-rs/atom/master/assets/swap.png)

A [`swap`](https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.swap) is special as it allows
a reference to be exchanged without the risk of that pointer being freed, or stomped on. When a thread
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