共享内存与原子操作
探索如何使用 SharedArrayBuffer 和原子操作，在 WASM 与 JS 之间实现高性能并发数据访问
共享内存与原子操作 是 CoddyKit 上的免费 WebAssembly (WASM) for High Performance Apps 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 WebAssembly (WASM) for High Performance Apps 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 WebAssembly (WASM) for High Performance Apps 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
Concurrency & Shared Memory
When building high-performance applications, especially with WebAssembly, you often need to perform tasks concurrently. This means running parts of your code in parallel, perhaps across different threads.
For these concurrent tasks to work together efficiently, they often need to access and modify the same data. This is where shared memory comes in.
Why Not Just ArrayBuffer?
You might already know about ArrayBuffer for handling raw binary data in JavaScript. However, a standard ArrayBuffer cannot be directly shared between different execution contexts (like the main thread and a Web Worker, or between JavaScript and a WebAssembly thread).
Each context would get its own copy of the data, which is inefficient and complicated to synchronize for frequent updates.
Introducing SharedArrayBuffer
The solution for true concurrent data access is SharedArrayBuffer. It's a special type of ArrayBuffer that allows the same memory block to be accessed by multiple threads simultaneously.
This means your JavaScript main thread, Web Workers, and WebAssembly modules can all read from and write to the *exact same* underlying data, enabling efficient communication and complex parallel computations.
Security Headers for Sharing
Due to security vulnerabilities (like Spectre), using SharedArrayBuffer requires specific HTTP response headers to be set by the server:
Cross-Origin-Opener-Policy: same-originCross-Origin-Embedder-Policy: require-corp
These headers ensure that the document is in an isolated, cross-origin isolated browsing context, which is necessary for SharedArrayBuffer to function securely.
Creating SharedArrayBuffer in JS
Creating a SharedArrayBuffer is similar to creating a regular ArrayBuffer. You specify the size in bytes. Then, you can create a typed array view (like Int32Array) to easily interact with the memory.
const sharedBuffer = new SharedArrayBuffer(1024); // 1KB
const sharedArray = new Int32Array(sharedBuffer);
console.log("Shared buffer created!");
console.log("Size:", sharedArray.length * Int32Array.BYTES_PER_ELEMENT, "bytes");WASM's View of Shared Memory
When a SharedArrayBuffer is passed to a WebAssembly module (e.g., via WebAssembly.Memory), WASM can map this memory into its own linear memory space. This allows WASM code to directly read and write to the shared data.
This direct access is key for performance, as it avoids costly data copying between the host environment (JavaScript) and the WASM module.
Race Conditions & Data Safety
While sharing memory is powerful, it introduces a challenge: race conditions. If multiple threads try to read and write to the same memory location at the same time, the final result can be unpredictable or incorrect.
Imagine two threads trying to increment a counter simultaneously. Without proper synchronization, one update might overwrite another, leading to a wrong count.
Introducing Atomics for Safety
To prevent race conditions, JavaScript provides the Atomics object. Atomics offer a set of operations that are guaranteed to be atomic, meaning they are indivisible.
An atomic operation either completes entirely or doesn't happen at all, ensuring that no other thread can interrupt it. This guarantees data integrity in shared memory.
Atomic Reads and Writes
The most basic atomic operations are `Atomics.load()` and `Atomics.store()`. These methods ensure that reading and writing values to a shared memory location happens as a single, uninterruptible step.
const sharedBuffer = new SharedArrayBuffer(4); // 4 bytes
const int32View = new Int32Array(sharedBuffer);
// Safely store a value at index 0
Atomics.store(int32View, 0, 100);
console.log("Stored 100 atomically.");
// Safely load a value from index 0
const value = Atomics.load(int32View, 0);
console.log("Loaded value:", value);Atomic Arithmetic Operations
Beyond simple reads/writes, Atomics provide arithmetic operations like Atomics.add(), Atomics.sub(), Atomics.and(), etc. These perform an operation and update the value atomically.
Atomics.add(typedArray, index, value) adds value to the element at index and returns the old value at that index, all in one safe step.
const sharedBuffer = new SharedArrayBuffer(4);
const int32View = new Int32Array(sharedBuffer);
Atomics.store(int32View, 0, 5); // Initial value
console.log("Initial value:", Atomics.load(int32View, 0));
// Atomically add 3 to the value at index 0
const oldValue = Atomics.add(int32View, 0, 3);
console.log("Old value before add:", oldValue);
console.log("New value after add:", Atomics.load(int32View, 0));Shared Memory Check
Consider the following JavaScript code snippet. Assume sharedBuffer is a properly configured SharedArrayBuffer and int32View is an Int32Array view of it.
const int32View = new Int32Array(sharedBuffer);
Atomics.store(int32View, 0, 5);
const result = Atomics.add(int32View, 0, 2);
const finalValue = Atomics.load(int32View, 0);Recap: Shared Memory & Atomics
We've explored how SharedArrayBuffer enables efficient concurrent data access between JavaScript and WebAssembly by allowing multiple threads to access the same memory block.
To prevent data corruption from race conditions, we learned about Atomics, which provide safe, indivisible operations for reading, writing, and modifying data in shared memory.
These tools are crucial for building high-performance, multithreaded WebAssembly applications.
用 AI 导师学习 WebAssembly (WASM) for High Performance Apps — 免费
在浏览器中编写并运行真实代码，获得全天候 AI 导师的即时帮助，并在网页或应用中继续学习。
- 课程
- 12
- 课程
- 48
常见问题解答
「共享内存与原子操作」课时是免费的吗？
是的 — 「共享内存与原子操作」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 WebAssembly (WASM) for High Performance Apps 课程的其余内容，请升级到 CoddyKit PRO。 WebAssembly (WASM) for High Performance Apps 课程共包含 4 节课。
「共享内存与原子操作」这节课中我会学到什么？
探索如何使用 SharedArrayBuffer 和原子操作，在 WASM 与 JS 之间实现高性能并发数据访问 你通过在浏览器中直接运行的动手代码来练习 WebAssembly (WASM) for High Performance Apps，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 WebAssembly (WASM) for High Performance Apps 需要有经验吗？
无需任何先前经验。CoddyKit 上的 WebAssembly (WASM) for High Performance Apps 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。
「共享内存与原子操作」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 WebAssembly (WASM) for High Performance Apps 课中编写并运行代码吗？
能。每节 WebAssembly (WASM) for High Performance Apps 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。
此课程中的所有课时
- 传递复杂数据结构
- WASM 内存模型与管理
- 共享内存与原子操作
- 增长与管理线性内存