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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
<title>Idiomatic Wappers Around C</title>
<link rel="stylesheet" href="css/reset.css">
<link rel="stylesheet" href="css/reveal.css">
<link rel="stylesheet" href="css/theme/black.css">
<!-- Theme used for syntax highlighting of code -->
<link rel="stylesheet" href="lib/css/monokai.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement('link');
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match(/print-pdf/gi) ? 'css/print/pdf.css' : 'css/print/paper.css';
document.getElementsByTagName('head')[0].appendChild(link);
</script>
</head>
<body>
<div class="reveal">
<div class="slides">
<section>
<h1>Building a Safe, Idiomatic Rust Wrapper Around C</h1>
</section>
<section data-background-image="images/spatialos-diagram.png" data-background-size="contain"
data-background-position="left">
<section>
<h2>SpatialOS:</h2>
<h3>Some Background</h3>
</section>
<section>
<p>A networking layer for multiplayer games:</p>
<ul>
<li>Persistence</li>
<li>Scale</li>
<li>Simulation</li>
</ul>
</section>
<section>
<p>Provide direct support for popular game engines:</p>
<ul>
<li>Unity</li>
<li>Unreal Engine 4</li>
</ul>
</section>
<section>
<p>Supports multiple languages:</p>
<ul>
<li class="fragment">C++</li>
<li class="fragment">C#</li>
<li class="fragment">Java</li>
<li class="fragment">C</li>
<li class="fragment">RUST?<span class="fragment">?<span class="fragment">?<span
class="fragment">?<span class="fragment">?<span
class="fragment">?</span></span></span></span></span></li>
</ul>
</section>
</section>
<section>
<section>
<h2>The Connection Object and Thread Safety</h2>
</section>
<section data-markdown>
<textarea data-template>
```c
WORKER_API Worker_Connection* Worker_ConnectionFuture_Get(
Worker_ConnectionFuture* future,
const uint32_t* timeout_millis);
WORKER_API Worker_OpList* Worker_Connection_GetOpList(
Worker_Connection* connection,
uint32_t timeout_millis);
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct WorkerConnection {
raw: *mut Worker_Connection,
}
impl WorkerConnection {
pub fn get_op_list(&self) -> OpList {
Worker_Connection_GetOpList(self.raw, 0)
}
}
```
</textarea>
</section>
<section data-background-image="images/Thinking_Face_Emoji.png" data-background-size="contain">
<h3>Is it Send?</h3>
</section>
<section data-background-image="images/Thinking_Face_Emoji.png">
<h2>Is it Sync?</h2>
</section>
<section>
<img data-src="images/not-thread-safe.png">
</section>
<section data-background-image="https://media.giphy.com/media/lJNoBCvQYp7nq/giphy.gif">
<h2>
To the forums!
</h2>
</section>
<section>
<img data-src="images/no-thread-safety-guarantees.png">
</section>
<section data-background-image="images/praise-it.png" data-background-position="top">
<img data-src="images/maybe-thread-safe.png">
</section>
<section>
<blockquote>... or wrapping it in a mutex.</blockquote>
<p>It's safe to access from different threads, so long as only one thread accesses it at a time.</p>
</section>
<section>
<blockquote>It doesn't use global variables</blockquote>
<p>There's no shared state, methods mutate data within the struct in an unsynchronized way.</p>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct WorkerConnection {
raw: *mut Worker_Connection,
}
impl WorkerConnection {
pub fn get_op_list(&mut self) -> OpList { ... }
}
unsafe impl Send for WorkerConnection {}
unsafe impl Sync for WorkerConnection {}
```
</textarea>
</section>
</section>
<section>
<section>
<h2>Speaking of OpList...</h2>
</section>
<section data-markdown>
<textarea data-template>
```c
WORKER_API Worker_OpList* Worker_Connection_GetOpList(
Worker_Connection* connection,
uint32_t timeout_millis);
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```c
typedef enum Worker_OpType {
WORKER_OP_TYPE_DISCONNECT = 1,
WORKER_OP_TYPE_FLAG_UPDATE = 2,
WORKER_OP_TYPE_LOG_MESSAGE = 3,
WORKER_OP_TYPE_METRICS = 4,
WORKER_OP_TYPE_CRITICAL_SECTION = 5,
WORKER_OP_TYPE_ADD_ENTITY = 6,
WORKER_OP_TYPE_REMOVE_ENTITY = 7,
WORKER_OP_TYPE_RESERVE_ENTITY_ID_RESPONSE = 8,
WORKER_OP_TYPE_RESERVE_ENTITY_IDS_RESPONSE = 9,
// ... and so on
} Worker_OpType;
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```c
typedef struct Worker_Op {
uint8_t op_type;
union {
Worker_DisconnectOp disconnect;
Worker_FlagUpdateOp flag_update;
Worker_LogMessageOp log_message;
Worker_MetricsOp metrics;
Worker_CriticalSectionOp critical_section;
Worker_AddEntityOp add_entity;
// ... and so on
};
} Worker_Op;
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```csharp
// Get the latest operations
// received by the connection.
var opList = connection.GetOpList(0);
// Invoke callbacks.
dispatcher.Process(opList);
```
</textarea>
</section>
<section data-background-image="images/neutral-face.png" data-background-size="contain"></section>
<section data-markdown data-background-image="images/party-popper.png" data-background-size="contain"
data-background-position="left">
<textarea data-template>
```rust
#[derive(Debug)]
pub enum WorkerOp<'a> {
Disconnect(DisconnectOp),
AddEntity(AddEntityOp),
RemoveEntity(RemoveEntityOp),
AddComponent(AddComponentOp<'a>),
RemoveComponent(RemoveComponentOp),
ComponentUpdate(ComponentUpdateOp<'a>),
EntityQueryResponse(EntityQueryResponseOp<'a>),
// ... and so on
}
```
</textarea>
</section>
</section>
<section>
<section>
<h2>Playing With Pointers</h2>
</section>
<section data-markdown>
<textarea data-template>
```c
// Borrowed, read-only data.
typedef struct Worker_ComponentData {
void* reserved;
Worker_ComponentId component_id;
Schema_ComponentData* schema_type;
Worker_ComponentDataHandle* user_handle;
} Worker_ComponentData;
// Owned, mutable data.
Schema_ComponentData* Schema_CreateComponentData();
void Schema_DestroyComponentData(Schema_ComponentData* data);
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct SchemaComponentData {
raw: *mut Schema_ComponentData,
}
impl SchemaComponentData {
pub fn component_id(&self) -> ComponentId {
Schema_GetComponentDataComponentId(self.raw)
}
}
```
</textarea>
</section>
<section>
How do we differentiate between <em>owned</em> and <em>borrowed</em> data?
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct SchemaComponentData<'a> {
raw: *mut Schema_ComponentData,
_marker: PhantomData<&'a Schema_ComponentData>,
}
impl SchemaComponentData {
pub fn new() -> SchemaComponentData<'static> {
Self {
raw: Schema_CreateComponentData(),
_marker: PhantomData,
}
}
}
```
</textarea>
</section>
<section data-markdown data-background-image="images/circle-with-slash.png"
data-background-size="contain">
<textarea data-template>
```rust
impl Drop for SchemaComponentData<'static> {
fn drop(&mut self) {
Schema_DestroyComponentData(self.raw);
}
}
```
</textarea>
</section>
<section data-background-image="images/three-weeks-later.jpg" data-background-size="contain"></section>
<section data-background-image="https://media.giphy.com/media/1SjmCkZsD0Wc0/giphy.gif"
data-background-size="cover"></section>
<section data-background-image="https://media.giphy.com/media/Q9kgQp6ptfcLS/giphy.gif">
<h2>What if we <em>LIED</em>?</h2>
</section>
<section>
<ul>
<li>The data is completely opaque</li>
<li>We never dereference the pointer</li>
<li>All we care about is the value of the pointer</li>
</ul>
</section>
<section>
<ul>
<li>Sometimes we own the data</li>
<li>Sometimes can mutate the data</li>
<li>Sometimes we can only read the data</li>
</ul>
</section>
<section>
<p>Rust has conventions for this:</p>
<ul>
<li><code>Box<T></code></li>
<li><code>&mut T</code></li>
<li><code>&T</code></li>
</ul>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct SchemaComponentData;
impl SchemaComponentData {
unsafe fn from_raw<'a>(
raw: *mut Schema_ComponentData,
) -> &'a SchemaComponentData {
&*(raw as *mut _)
}
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
impl SchemaComponentData {
pub fn component_id(&self) -> ComponentId {
let raw = self as *mut _;
Schema_GetComponentDataComponentId(raw)
}
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
impl Object {
pub fn add_object_field(
&mut self,
field: FieldId,
) -> &mut Object {
let raw = self as *mut _;
let result = Schema_AddObject(raw, field)
&mut *(result as *mut _)
}
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub trait Ownable {
type Raw;
unsafe fn destroy(me: *mut Self::Raw);
}
pub struct Owned<T: Ownable>(*mut T::Raw);
impl<T: Ownable> Drop for Owned<T> {
fn drop(&mut self) {
T::destroy(self.0.as_ptr());
}
}
```
</textarea>
</section>
<section data-markdown>
<textarea data-template>
```rust
impl SchemaComponentData {
pub fn new() -> Owned<SchemaComponentData> {
Owned(
Schema_CreateComponentData(),
)
}
}
impl Ownable for SchemaComponentData {
type Raw = Schema_ComponentData;
unsafe fn destroy(inst: *mut Self::Raw) {
Schema_DestroyComponentData(inst);
}
}
```
</textarea>
</section>
<section>
<h2>One more thing...</h2>
</section>
<section data-markdown>
<textarea data-template>
```rust
pub struct SchemaComponentData(
PhantomData<*mut Schema_ComponentData>,
);
unsafe impl Send for SchemaComponentData {}
```
</textarea>
</section>
</section>
<section>
The End
</section>
</div>
</div>
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