我想将数组和切片放在堆栈上，例如C ++中的std :: array和C中的数组，对此感到很奇怪。该堆栈由Vincent Blanchon在“ 转到：Goroutine堆栈大小如何演变”一文中写得很好。。Vincent谈到了goroutines中的堆栈更改。综上所述：
- 最小堆栈大小2 KB；
- 最大大小取决于体系结构，在64位体系结构1 GB上；
- 每次堆栈大小加倍时；
- 堆栈既增加又减少。
我将找出可以放入堆栈的数量以及可以带来多少开销。我将使用从源代码编译的go 1.13.8，其中包含调试信息和编译选项-gcflags=-m。
要在程序运行时获取调试输出，应将runtime/stack.go常数stackDebug设置为所需的值：
const (
stackDebug = 0
)
很简单的程序
我将从一个不执行任何操作的程序开始，以查看堆栈如何在主要goroutine中脱颖而出：
package main
func main() {
}
我们将看到全局池中如何填充第2、8、32 KB段：
$ GOMAXPROCS=1 ./app
stackalloc 32768
allocated 0xc000002000
stackalloc 2048
stackcacherefill order=0
allocated 0xc000036000
stackalloc 32768
allocated 0xc00003a000
stackalloc 8192
stackcacherefill order=2
allocated 0xc000046000
stackalloc 2048
allocated 0xc000036800
stackalloc 2048
allocated 0xc000037000
stackalloc 2048
allocated 0xc000037800
stackalloc 32768
allocated 0xc00004e000
stackalloc 8192
allocated 0xc000048000
这是重要的一点。我们可以预期分配的内存将被重用。
程序不是很简单
哪里没有世界你好！
package main
import "fmt"
func helloWorld() {
fmt.Println("Hello world!")
}
func main() {
helloWorld()
}
runtime: newstack sp=0xc000036348 stack=[0xc000036000, 0xc000036800]
morebuf={pc:0x41463b sp:0xc000036358 lr:0x0}
sched={pc:0x4225b1 sp:0xc000036350 lr:0x0 ctxt:0x0}
stackalloc 4096
stackcacherefill order=1
allocated 0xc000060000
copystack gp=0xc000000180 [0xc000036000 0xc000036350 0xc000036800] -> [0xc000060000 0xc000060b50 0xc000061000]/4096
stackfree 0xc000036000 2048
stack grow done
stackalloc 2048
allocated 0xc000036000
Hello world!
2 KB的大小是不够的，分配了4 KB的块。我们将在方括号中处理数字。这些是地址；在边缘，这是结构值：
type stack struct {
lo uintptr
hi uintptr
}
在中间，这是一个地址，指示使用了多少堆栈，计算方法如下：
used := old.hi - gp.sched.sp
print("copystack gp=", gp, " [", hex(old.lo), " ", hex(old.hi-used), " ", hex(old.hi), "]", " -> [", hex(new.lo), " ", hex(new.hi-used), " ", hex(new.hi), "]/", newsize, "\n")
:
- :
package main
import (
"fmt"
"time"
)
func helloWorld() {
fmt.Println("Hello world!")
}
func main() {
for i := 0 ; i< 12 ; i++ {
go helloWorld()
}
time.Sleep(5*time.Second)
}
$ ./app 2>&1 | grep "alloc 4"
stackalloc 4096
stackalloc 4096
stackalloc 4096
stackalloc 4096
stackalloc 4096
, . .
stack_test.go , . bigsize, go build -gcflags=-m main.go:8:6: moved to heap: x.
package main
const bigsize = 1024*1024*10
const depth = 50
func step(i int) byte {
var x [bigsize]byte
if i != depth {
return x[i] * step(i+1)
} else {
return x[i]
}
}
func main() {
step(0)
}
10 MB, depth > 50 stack overflow:
runtime: goroutine stack exceeds 1000000000-byte limit
fatal error: stack overflow
, -gcflags="-m"
package main
import (
"fmt"
"os"
)
const bigsize = 1024 * 1024 * 10
func readSelf(buff []byte) int {
f, err := os.Open("main.go")
if err != nil {
panic(err)
}
count, _ := f.Read(buff)
if err := f.Close(); err != nil {
panic(err)
}
return count
}
func printSelf(buff []byte, count int) {
tmp := string(buff[:count])
fmt.Println(tmp)
}
func foo() {
var data [bigsize]byte
cnt := readSelf(data[:])
printSelf(data[:], cnt)
}
func main() {
foo()
}
, , :
stackalloc 2048
stackcacherefill order=0
allocated 0xc000042000
runtime: newstack sp=0xc00008ef40 stack=[0xc00008e000, 0xc00008f000]
morebuf={pc:0x48e4e0 sp:0xc00008ef50 lr:0x0}
sched={pc:0x48e4b8 sp:0xc00008ef48 lr:0x0 ctxt:0x0}
stackalloc 8192
stackcacherefill order=2
allocated 0xc000078000
copystack gp=0xc000000180 [0xc00008e000 0xc00008ef48 0xc00008f000] -> [0xc000078000 0xc000079f48 0xc00007a000]/8192
stackfree 0xc00008e000 4096
stack grow done
...
runtime: newstack sp=0xc0010aff40 stack=[0xc0008b0000, 0xc0010b0000]
morebuf={pc:0x48e4e0 sp:0xc0010aff50 lr:0x0}
sched={pc:0x48e4b8 sp:0xc0010aff48 lr:0x0 ctxt:0x0}
stackalloc 16777216
allocated 0xc0010b0000
copystack gp=0xc000000180 [0xc0008b0000 0xc0010aff48 0xc0010b0000] -> [0xc0010b0000 0xc0020aff48 0xc0020b0000]/16777216
stackfree 0xc0008b0000 8388608
stack grow done
, .
64 KB :
package main
import (
"fmt"
"os"
)
const bigsize = 1024*64 - 1
func readSelf(buff []byte) int {
f, err := os.Open("main.go")
if err != nil {
panic(err)
}
count, _ := f.Read(buff)
if err := f.Close(); err != nil {
panic(err)
}
return count
}
func printSelf(buff []byte, count int) {
tmp := string(buff[:count])
fmt.Println(tmp)
}
func foo() {
data := make([]byte, bigsize)
cnt := readSelf(data)
printSelf(data, cnt)
}
func main() {
foo()
}
stackalloc 131072
allocated 0xc0000d0000
copystack gp=0xc000000180 [0xc0000c0000 0xc0000cff48 0xc0000d0000] -> [0xc0000d0000 0xc0000eff48 0xc0000f0000]/131072
stackfree 0xc0000c0000 65536
Go (zero values). . , sync.Pool.
:
, , .
func readSelf(buff []byte) int {
f, err := os.Open("bench_test.go")
if err != nil {
panic(err)
}
count, err := f.Read(buff)
if err != nil {
panic(err)
}
if err := f.Close(); err != nil {
panic(err)
}
return count
}
func printSelf(buff []byte, count int) {
f, err := os.OpenFile(os.DevNull, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
if err != nil {
panic(err)
}
if _, err := f.Write(buff[:count]); err != nil {
panic(err)
}
if err := f.Close(); err != nil {
panic(err)
}
}
func usePoolBlock4k() {
inputp := pool4blocks.Get().(*[]byte)
outputp := pool4blocks.Get().(*[]byte)
cnt := readSelf(*inputp)
copy(*outputp, *inputp)
printSelf(*outputp, cnt)
pool4blocks.Put(inputp)
pool4blocks.Put(outputp)
}
func useStackBlock4k() {
var input [block4k]byte
var output [block4k]byte
cnt := readSelf(input[:])
copy(output[:], input[:])
printSelf(output[:], cnt)
}
func BenchmarkPoolBlock4k(b *testing.B) {
runtime.GC()
for i := 0; i < 8; i++ {
data := pool4blocks.Get()
pool4blocks.Put(data)
}
for i := 0; i < 8; i++ {
usePoolBlock4k()
}
b.ResetTimer()
for i := 0; i < b.N; i++ {
usePoolBlock4k()
}
}
func BenchmarkStackBlock4k(b *testing.B) {
runtime.GC()
for i := 0; i < 8; i++ {
useStackBlock4k()
}
b.ResetTimer()
for i := 0; i < b.N; i++ {
useStackBlock4k()
}
}
$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: gostack/04_benchmarks
BenchmarkPoolBlock4k-12 312918 3804 ns/op 256 B/op 8 allocs/op
BenchmarkStackBlock4k-12 313255 3833 ns/op 256 B/op 8 allocs/op
BenchmarkPoolBlock8k-12 300796 3980 ns/op 256 B/op 8 allocs/op
BenchmarkStackBlock8k-12 294266 4110 ns/op 256 B/op 8 allocs/op
BenchmarkPoolBlock16k-12 288734 4138 ns/op 256 B/op 8 allocs/op
BenchmarkStackBlock16k-12 269382 4408 ns/op 256 B/op 8 allocs/op
BenchmarkPoolBlock32k-12 272139 4407 ns/op 256 B/op 8 allocs/op
BenchmarkStackBlock32k-12 240339 4957 ns/op 256 B/op 8 allocs/op
PASS
4 KB, . , . :
(pprof) top 15
Showing nodes accounting for 7.99s, 79.58% of 10.04s total
Dropped 104 nodes (cum <= 0.05s)
Showing top 15 nodes out of 85
flat flat% sum% cum cum%
3.11s 30.98% 30.98% 3.38s 33.67% syscall.Syscall6
2.01s 20.02% 51.00% 2.31s 23.01% syscall.Syscall
0.83s 8.27% 59.26% 0.83s 8.27% runtime.epollctl
0.60s 5.98% 65.24% 0.60s 5.98% runtime.memmove
0.21s 2.09% 67.33% 0.21s 2.09% runtime.unlock
0.18s 1.79% 69.12% 0.18s 1.79% runtime.nextFreeFast
0.14s 1.39% 70.52% 0.33s 3.29% runtime.exitsyscall
0.14s 1.39% 71.91% 0.21s 2.09% runtime.reentersyscall
0.13s 1.29% 73.21% 0.46s 4.58% runtime.mallocgc
0.12s 1.20% 74.40% 1.25s 12.45% gostack/04_benchmarks.useStackBlock32k
0.12s 1.20% 75.60% 0.13s 1.29% runtime.exitsyscallfast
0.11s 1.10% 76.69% 0.45s 4.48% runtime.SetFinalizer
0.11s 1.10% 77.79% 0.11s 1.10% runtime.casgstatus
0.10s 1% 78.78% 0.13s 1.29% runtime.deferreturn
0.08s 0.8% 79.58% 1.24s 12.35% gostack/04_benchmarks.useStackBlock16k
syscalls. useStackBlock32k getFromStack32k. 120ms:
(pprof) list useStackBlock32k
Total: 10.04s
ROUTINE ======================== useStackBlock32k in bench_test.go
120ms 1.25s (flat, cum) 12.45% of Total
. . 158: printSelf(output[:], cnt)
. . 159:}
. . 160:
. . 161://go:noinline
. . 162:func useStackBlock32k() {
90ms 90ms 163: var input [block32k]byte
30ms 30ms 164: var output [block32k]byte
. . 165:
. 530ms 166: cnt := readSelf(input[:])
. 160ms 167: copy(output[:], input[:])
. 440ms 168: printSelf(output[:], cnt)
. . 169:}
ROUTINE ======================== usePoolBlock32k in bench_test.go
10ms 1.18s (flat, cum) 11.75% of Total
. . 115: pool16blocks.Put(outputp)
. . 116:}
. . 117:
. . 118://go:noinline
. . 119:func usePoolBlock32k() {
. 10ms 120: inputp := pool32blocks.Get().(*[]byte)
. 10ms 121: outputp := pool32blocks.Get().(*[]byte)
. . 122:
. 520ms 123: cnt := readSelf(*inputp)
10ms 200ms 124: copy(*outputp, *inputp)
. 440ms 125: printSelf(*outputp, cnt)
. . 126:
. . 127: pool32blocks.Put(inputp)
. . 128: pool32blocks.Put(outputp)
. . 129:}
:
- 10 MB;
- 64 KB;
- 拆分堆栈有开销；
- 零值存在开销。