Node.js setImmediate的使用小结

setImmediate(() => {
  console.log('这段代码将在当前事件循环周期结束后立即执行');
});

console.log('这段代码将先执行');

setTimeout(() => {
  console.log('setTimeout');
}, 0);

setImmediate(() => {
  console.log('setImmediate');
});

process.nextTick(() => {
  console.log('nextTick');
});

console.log('主程序');

const immediateId = setImmediate(() => {
  console.log('这段代码不会执行');
});

clearImmediate(immediateId);

function processBigData(data) {
  // 避免阻塞事件循环
  setImmediate(() => {
    // 处理大量数据
    const result = performHeavyComputation(data);
    console.log('处理完成');
  });
}

function processItems(items, i = 0) {
  if (i === items.length) return;
  
  // 处理当前项
  console.log(`处理项目 ${items[i]}`);
  
  // 使用setImmediate递归处理下一项，避免堆栈溢出
  setImmediate(() => {
    processItems(items, i + 1);
  });
}

// 处理大量项目
processItems(Array.from({ length: 10000 }, (_, i) => i));

function ensureAsync(fn) {
  return function(...args) {
    const callback = args[args.length - 1];
    const newArgs = args.slice(0, -1);
    
    setImmediate(() => {
      try {
        const result = fn(...newArgs);
        callback(null, result);
      } catch (err) {
        callback(err);
      }
    });
  };
}

const asyncOperation = ensureAsync((x) => x * 2);

asyncOperation(5, (err, result) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(result); // 输出: 10
});

// 浏览器中的 setImmediate polyfill
if (!window.setImmediate) {
  window.setImmediate = function(callback, ...args) {
    return setTimeout(() => callback(...args), 0);
  };
  
  window.clearImmediate = function(id) {
    clearTimeout(id);
  };
}

const http = require('http');
const fs = require('fs');

const server = http.createServer((req, res) => {
  // 读取大文件
  fs.readFile('largeFile.txt', (err, data) => {
    if (err) {
      res.statusCode = 500;
      res.end('服务器错误');
      return;
    }
    
    // 使用 setImmediate 处理数据，确保不阻塞其他请求
    setImmediate(() => {
      const processedData = processData(data);
      res.end(processedData);
    });
  });
});

server.listen(3000);

function processData(data) {
  // 假设这是一个CPU密集型操作
  return data.toString().toUpperCase();
}