package main

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

var globalSum int64

// 进一步增加循环次数，单任务耗时延长到10秒以上
func longCPUTask(id int) {
	localSum := int64(0)
	loopCount := int64(500000000) * int64(id+1) // 循环次数：5e8→2e9（耗时≈10s→40s）
	for j := int64(1); j < loopCount; j++ {
		localSum = (localSum + j*j%987654321) * 1000000007 % 123456789
		if j%100000000 == 0 { // 极低频率写入全局变量，最大化独占P时间
			globalSum = localSum
		}
	}
}

func main() {
	runtime.GOMAXPROCS(1)
	var wg sync.WaitGroup
	startTime := time.Now()
	taskDurations := make([]time.Duration, 4)

	for i := 0; i < 4; i++ {
		wg.Add(1)
		id := i
		go func() {
			defer wg.Done()
			taskStart := time.Now()
			longCPUTask(id)
			taskDurations[id] = time.Since(taskStart)
		}()
	}

	wg.Wait()
	totalDuration := time.Since(startTime)

	fmt.Println("GOMAXPROCS=1")
	sumDurations := time.Duration(0)
	for i := 0; i < 4; i++ {
		fmt.Printf("任务%d 耗时: %v\n", i, taskDurations[i])
		sumDurations += taskDurations[i]
	}
	fmt.Printf("总耗时: %v, 4个任务之和: %v（接近）\n", totalDuration, sumDurations)
}