Javascript 简明教程
JavaScript - Atomics Objects
JavaScript 中的 Atomics 对象提供了一组用于对 SharedArrayBuffer 对象执行原子操作的静态方法。原子操作是保证在单一步骤中完成的操作,不会被其他线程中断。这使其对于实现并发数据结构和算法非常有用。
作为 ECMAScript 标准的一部分,JavaScript 中的 Atomics 对象作为在多线程环境中管理共享内存的关键工具。让我们更详细地了解原子操作的基本概念:
Atomics Object
Atomics 对象是内置的 JavaScript 对象,对共享内存执行原子操作。它设计为在多线程环境中使用,在该环境中,多个线程或 Web 工作人员可能同时访问和修改共享数据。
The Essence of "Atomic"
在 Atomics 对象的上下文中,“原子”表示至关重要的特性:它执行本质上不可分割的操作。当我们将一项操作声明为原子操作时;我们暗示它的执行将像单一单元一样持续、不间断地发生。这种品质对于防止竞争条件至关重要;当并发操作的结果取决于它们的时序和执行顺序时,就会出现这种情况。
Atomic Operations
原子操作是在共享的内存上的低级操作,有保证能执行为一个独立、不可中断的单元。这些操作包括加法、减法、位运算、交换等。
Atomics 对象提供了诸如 add、sub、and、or、xor、load、store、exchange 等方法,每个对应一个特定的原子操作。
Sr.No. |
Method & Description |
1 |
Atomics.add() 向类型化数组中特定索引处的元素添加一个指定的值。以原子方式返回原始值。 |
2 |
Atomics.sub() 从类型化数组中特定索引处的元素中减去一个指定的值。以原子方式返回原始值。 |
3 |
Atomics.and() 对类型化数组中特定索引处的元素执行原子按位 AND 运算,并带有给定的值。以原子方式返回原始值。 |
4 |
Atomics.or() 对类型化数组中特定索引处的元素执行原子按位 OR 运算,并带有给定的值。以原子方式返回原始值。 |
5 |
Atomics.xor() 对类型化数组中特定索引处的元素执行原子按位 XOR 运算,并带有给定的值。以原子方式返回原始值。 |
6 |
Atomics.load() 以原子方式检索类型化数组中特定索引处的值。 |
7 |
Atomics.store() 以原子方式将给定的值存储到类型化数组的指定索引处。 |
8 |
Atomics.exchange() 将类型化数组中特定索引处的值与指定的值交换。以原子方式返回原始值。 |
9 |
Atomics. compareExchange() 将类型化数组中指定索引位置的值与提供的预期值进行比较,如果它们匹配,则用新值更新该值。原子上返回原始值。 |
10 |
Atomics.wait() 原子地等待类型化数组中指定索引位置的值为特定值,然后返回。允许在各个线程间进行有效的协调。 |
11 |
Atomics.notify() 原子地通知与类型化数组中指定索引位置相关的等待队列。 |
Examples
Example 1: Basic Usage of Atomics Operations
在本例中,针对共享内存上的基本原子操作演示了Atomics对象。这些操作包括加法、减法、按位AND运算、OR运算、XOR运算、加载、存储、交换和比较-交换值。每个操作确保了执行单元的不可分割性,这对于防止多线程环境中的竞争条件至关重要。
Atomics.add()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.add()
const originalAddValue = Atomics.add(sharedArray, 0, 10);
console.log(`Atomics.add: Original value: ${originalAddValue}, New value: ${sharedArray[0]}`);
Atomics.add: Original value: 0, New value: 10
Atomics.add()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.sub()
const originalSubValue = Atomics.sub(sharedArray, 0, 5);
console.log(`Atomics.sub: Original value: ${originalSubValue}, New value: ${sharedArray[0]}`);
Atomics.sub: Original value: 10, New value: 5
Atomics.add()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.and()
const originalAndValue = Atomics.and(sharedArray, 0, 0b1010);
console.log(`Atomics.and: Original value: ${originalAndValue}, New value: ${sharedArray[0].toString(2)}`);
Atomics.and: Original value: 5, New value: 0
Atomics.or()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.or()
const originalOrValue = Atomics.or(sharedArray, 0, 0b1100);
console.log(`Atomics.or: Original value: ${originalOrValue}, New value: ${sharedArray[0].toString(2)}`);
Atomics.or: Original value: 0, New value: 1100
Atomics.xor()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.xor()
const originalXorValue = Atomics.xor(sharedArray, 0, 0b0110);
console.log(`Atomics.xor: Original value: ${originalXorValue}, New value: ${sharedArray[0].toString(2)}`);
Atomics.xor: Original value: 12, New value: 1010
Atomics.load()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.load()
const loadedValue = Atomics.load(sharedArray, 0);
console.log(`Atomics.load: Loaded value: ${loadedValue}`);
Atomics.load: Loaded value: 10
Atomics.store()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.store()
Atomics.store(sharedArray, 0, 42);
console.log(`Atomics.store: New value: ${sharedArray[0]}`);
Atomics.store: New value: 42
Atomics.exchange()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.exchange()
const originalExchangeValue = Atomics.exchange(sharedArray, 0, 99);
console.log(`Atomics.exchange: Original value: ${originalExchangeValue}, New value: ${sharedArray[0]}`);
Atomics.exchange: Original value: 42, New value: 99
Atomics.compareExchange()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.compareExchange()
const expectedValue = 99;
const newValue = 55;
const successfulCompareExchange = Atomics.compareExchange(sharedArray, 0, expectedValue, newValue);
console.log(`Atomics.compareExchange: Operation was${successfulCompareExchange ? ' ' : ' not '}successful. New value: ${sharedArray[0]}`);
Atomics.compareExchange: Operation was successful. New value: 55
Atomics.wait()
// Shared memory setup
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Atomics.wait()
const valueToWaitFor = 55;
Atomics.store(sharedArray, 0, valueToWaitFor);
setTimeout(() => {
Atomics.notify(sharedArray, 0);
}, 2000);
const waitResult = Atomics.wait(sharedArray, 0, valueToWaitFor, 5000);
console.log(`Atomics.wait: Wait result: ${waitResult}`);
Atomics.wait: Wait result: timed-out
Example 2: Real-World Use Case - Synchronized Counter
在这种实际场景中,我们使用 Atomics 对象来构建一个同步计数器;多个线程通过使用 Atomics.add() 操作来递增该计数器,从而保证更新过程中的原子性。这种应用程序显而易见地显示了有效线程协调的功能和必要性:它在多线程环境中提供实用的数据管理解决方案。
const sharedBuffer = new SharedArrayBuffer(4);
const sharedArray = new Int32Array(sharedBuffer);
// Synchronized counter
function incrementCounter() {
const incrementValue = 1;
const originalValue = Atomics.add(sharedArray, 0, incrementValue);
console.log(`Incremented counter by ${incrementValue}. New value: ${sharedArray[0]}`);
}
// Multiple threads incrementing the counter
setInterval(() => {
incrementCounter();
}, 1000);
// Simulate other activities in the main thread
setInterval(() => {
console.log('Main thread doing other work.');
}, 3000);
Incremented counter by 1. New value: 1
Incremented counter by 1. New value: 2
Main thread doing other work.
Incremented counter by 1. New value: 3
Incremented counter by 1. New value: 4
Incremented counter by 1. New value: 5
Main thread doing other work.
Incremented counter by 1. New value: 6
Incremented counter by 1. New value: 7
Incremented counter by 1. New value: 8
Main thread doing other work.
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