我有一个大学项目,当我使用1个goroutine,2个goroutine,3个等等时,测试矩阵乘法的时间差。我必须使用频道。我的问题是,不管我添加多少go例程,编译时间几乎总是相同。也许有人可以说出问题所在。也许发送时间很长,而且发送时间很长。代码如下
package main
import (
"fmt"
"math/rand"
"time"
)
const length = 1000
var start time.Time
var rez [length][length]int
func main() {
const threadlength = 1
toCalcRow := make(chan []int)
toCalcColumn := make(chan []int)
dummy1 := make(chan int)
dummy2 := make(chan int)
var row [length + 1]int
var column [length + 1]int
var a [length][length]int
var b [length][length]int
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
a[i][j] = rand.Intn(10)
b[i][j] = rand.Intn(10)
}
}
for i := 0; i < threadlength; i++ {
go Calc(toCalcRow, toCalcColumn, dummy1, dummy2)
}
start = time.Now()
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
row[0] = i
column[0] = j
for k := 0; k < length; k++ {
row[k+1] = a[i][j]
column[k+1] = b[i][k]
}
rowSlices := make([]int, len(row))
columnSlices := make([]int, len(column))
copy(rowSlices, row[:])
copy(columnSlices, column[:])
toCalcRow <- rowSlices
toCalcColumn <- columnSlices
}
}
dummy1 <- -1
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
fmt.Print(rez[i][j])
fmt.Print(" ")
}
fmt.Println(" ")
}
<-dummy2
close(toCalcRow)
close(toCalcColumn)
close(dummy1)
}
func Calc(chin1 <-chan []int, chin2 <-chan []int, dummy <-chan int, dummy1 chan<- int) {
loop:
for {
select {
case row := <-chin1:
column := <-chin2
var sum [3]int
sum[0] = row[0]
sum[1] = column[0]
for i := 1; i < len(row); i++ {
sum[2] += row[i] * column[i]
}
rez[sum[0]][sum[1]] = sum[2]
case <-dummy:
elapsed := time.Since(start)
fmt.Println("Binomial took ", elapsed)
dummy1 <- 0
break loop
}
}
close(dummy1)
}
您没什么区别,因为准备将数据传递给go例程是您的瓶颈。它比执行calc慢或快。
传递行和列的副本不是一个好策略。这会破坏性能。
go例程可以直接从只读的输入矩阵中读取数据。这里没有可能的比赛条件。
与输出相同。如果go例程计算行与列的乘法,它将结果写入不同的单元格中。这里也没有可能的比赛条件。
该做什么。用两个字段定义一个结构,一个用于行,一个用于列以相乘。
用行和列的所有可能组合填充缓冲的通道,以从(0,0)乘以(n-1,m-1)。
go例程,使用通道中的结构,执行计算并将结果直接写入输出矩阵。
然后,您还有一个完成的通道,可以向main go例程发出信号,通知计算已完成。当go例程完成对结构(n-1,m-1)的处理后,它将关闭完成的通道。
main go例程在编写完所有结构后,在完成的通道上等待。关闭完工通道后,它将打印经过的时间。我们可以使用一个等待组来等待所有go例程终止其计算。
然后,您可以开始执行一次go例程,并增加go例程的数量,以查看处理时间的影响。
查看代码:
package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
type pair struct {
row, col int
}
const length = 1000
var start time.Time
var rez [length][length]int
func main() {
const threadlength = 1
pairs := make(chan pair, 1000)
var wg sync.WaitGroup
var a [length][length]int
var b [length][length]int
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
a[i][j] = rand.Intn(10)
b[i][j] = rand.Intn(10)
}
}
wg.Add(threadlength)
for i := 0; i < threadlength; i++ {
go Calc(pairs, &a, &b, &rez, &wg)
}
start = time.Now()
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
pairs <- pair{row: i, col: j}
}
}
wg.Wait()
elapsed := time.Since(start)
fmt.Println("Binomial took ", elapsed)
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
fmt.Print(rez[i][j])
fmt.Print(" ")
}
fmt.Println(" ")
}
}
func Calc(pairs chan pair, a, b, rez *[length][length]int, wg *sync.WaitGroup) {
for {
pair, ok := <-pairs
if !ok {
break
}
rez[pair.row][pair.col] = 0
for i := 0; i < length; i++ {
rez[pair.row][pair.col] += a[pair.row][i] * b[i][pair.col]
}
if pair.row == length-1 && pair.col == length-1 {
close(pairs)
}
}
wg.Done()
}
您的代码非常难于遵循(调用变量dummy1 / dummy2尤其令人困惑,尤其是当它们在Calc
中获得不同的名称时),并添加一些注释将使其更容易理解。
首先是一个错误。发送要计算的数据后,您dummy1 <- -1
,我相信您希望它等待所有计算完成。但是,当您有多个goroutine时,不一定是这种情况。该通道将被其中一个goroutine耗尽,并打印出定时信息。其他goroutine仍将运行(并且可能尚未完成其计算)。
就时间而言,我怀疑您将数据发送到go例程的方式会使速度变慢;您先发送行,然后发送列;因为未缓冲通道,所以goroutine将在等待列时阻塞(切换回主goroutine发送列)。这种来回回落会减慢您的goroutine获取数据的速度,并且可以很好地解释为什么添加额外的goroutine影响有限(如果使用缓冲通道,也会变得很危险)。
我已经将您的代码重构(请注意,可能存在错误,而且还远远不够完美!)到确实显示出差异的地方(在我的计算机上,1 goroutine = 10s; 5 = 7s):
package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
const length = 1000
var start time.Time
var rez [length][length]int
// toMultiply will hold details of what the goroutine will be multiplying (one row and one column)
type toMultiply struct {
rowNo int
columnNo int
row []int
column []int
}
func main() {
const noOfGoRoutines = 5
// Build up a matrix of dimensions (length) x (length)
var a [length][length]int
var b [length][length]int
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
a[i][j] = rand.Intn(10)
b[i][j] = rand.Intn(10)
}
}
// Setup completed so start the clock...
start = time.Now()
// Start off threadlength go routines to multiply each row/column
toCalc := make(chan toMultiply)
var wg sync.WaitGroup
wg.Add(noOfGoRoutines)
for i := 0; i < noOfGoRoutines; i++ {
go func() {
Calc(toCalc)
wg.Done()
}()
}
// Begin the multiplication.
start = time.Now()
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
tm := toMultiply{
rowNo: i,
columnNo: j,
row: make([]int, length),
column: make([]int, length),
}
for k := 0; k < length; k++ {
tm.row[k] = a[i][j]
tm.column[k] = b[i][k]
}
toCalc <- tm
}
}
// All of the data has been sent to the chanel; now we need to wait for all of the
// goroutines to complete
close(toCalc)
wg.Wait()
fmt.Println("Binomial took ", time.Since(start))
// The full result should be in tz
for i := 0; i < length; i++ {
for j := 0; j < length; j++ {
//fmt.Print(rez[i][j])
//fmt.Print(" ")
}
//fmt.Println(" ")
}
}
// Calc - Multiply a row from one matrix with a column from another
func Calc(toCalc <-chan toMultiply) {
for tc := range toCalc {
var result int
for i := 0; i < len(tc.row); i++ {
result += tc.row[i] * tc.column[i]
}
// warning - the below should work in this case but be careful writing to global variables from goroutines
rez[tc.rowNo][tc.columnNo] = result
}
}