golang之string类型变量操作的原子性

留言

在并发场景下，string跟map一样，都是需要使用atomic包/sync包来保证读写的原子性。


str_atom.go:

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package main

import (
	"fmt"
	"time"
)

var a = "0"

func main() {

	ch := make(chan string)

	go func() {
		i := 1

		for {

			if i%2 == 0 {
				a = "0"
			} else {
				a = "aa"
			}
			// 如果将sleep去掉，则会读不到脏数据，原因在于编译器做了优化
			time.Sleep(1 * time.Millisecond)
			i++
		}
	}()

	go func() {
		for {
			b := a
			if b != "0" && b != "aa" {
				ch <- b
			}
		}
	}()

	for i := 0; i < 10; i++ {
		fmt.Println("Got strange string: ", <-ch)
	}

}


按预期, ch 不可能被写入,因为 b 的值只可能是 “0” 或 “aa”.

但实际运行:

(即起两个协程,一个不停对a重新赋值,另一个选出a的值不为”0”或”aa”的,存入一个channel,并打印. 当有10次不为”0”或”aa”后,结束打印,程序运行完成)

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Got strange string:  05
Got strange string:  a
Got strange string:  a
Got strange string:  05
Got strange string:  05
Got strange string:  a
Got strange string:  a
Got strange string:  a
Got strange string:  a
Got strange string:  a

在Linux上输出为05,在Mac上05会输出为0:


b的值为什么会存在 “a”或者”05”(or”0:”)的情况 ??


这是因为,string类型并不是并发安全的.


string的内部结构：

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struct {
		str uintptr
		len int
	}

对 string 赋值,并不是原子操作,而是会分为两步,(其实是对上面这个struct ，Go 无法保证原子性地完成赋值)

因此可能会出现 goroutine 1 刚修改完指针（str）、还没来得及修改长度（len），goroutine 2 就读取了这个string 的情况。

str 改了、len 还没来得及改,即 str="aa",len=1, 和str="0",len=2, 对应”莫名其妙”出现的 “a”和”05”（或”0:”）


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func main() {

	var str string = "0"
	p := (*struct {
		str uintptr
		len int
	})(unsafe.Pointer(&str))

	spew.Dump(p)

}

输出:

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(*struct { str uintptr; len int })(0xc00008e2b0)({
 str: (uintptr) 0x1101b01,
 len: (int) 1
})

思考:

str="aa",len=1,变为”a”容易理解,但str="0",len=2为什么会是”05”(or“0:”)呢?


go tool compile -S -S str_atom.go 得到汇编代码：（go 1.17,arm64）

也可将源码复制到该网站，在线查看汇编

`go tool compile -S -S str_atom.go` 
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"".main<1> STEXT size=304 args=0x0 locals=0x88 funcid=0x0
	0x0000 00000 (str_atom.go:10)	TEXT	"".main(SB), ABIInternal, $144-0
	0x0000 00000 (str_atom.go:10)	MOVD	16(g), R1
	0x0004 00004 (str_atom.go:10)	PCDATA	$0, $-2
	0x0004 00004 (str_atom.go:10)	SUB	$16, RSP, R2
	0x0008 00008 (str_atom.go:10)	CMP	R1, R2
	0x000c 00012 (str_atom.go:10)	BLS	288
	0x0010 00016 (str_atom.go:10)	PCDATA	$0, $-1
	0x0010 00016 (str_atom.go:10)	MOVD.W	R30, -144(RSP)
	0x0014 00020 (str_atom.go:10)	MOVD	R29, -8(RSP)
	0x0018 00024 (str_atom.go:10)	SUB	$8, RSP, R29
	0x001c 00028 (str_atom.go:10)	FUNCDATA	ZR, gclocals·7d2d5fca80364273fb07d5820a76fef4(SB)
	0x001c 00028 (str_atom.go:10)	FUNCDATA	$1, gclocals·1373f50311b358236be33e875131d17d(SB)
	0x001c 00028 (str_atom.go:10)	FUNCDATA	$2, "".main.stkobj(SB)
	0x001c 00028 (str_atom.go:12)	MOVD	$type.chan string(SB), R0
	0x0024 00036 (str_atom.go:12)	MOVD	R0, 8(RSP)
	0x0028 00040 (str_atom.go:12)	MOVD	ZR, 16(RSP)
	0x002c 00044 (str_atom.go:12)	PCDATA	$1, ZR
	0x002c 00044 (str_atom.go:12)	CALL	runtime.makechan(SB)
	0x0030 00048 (str_atom.go:12)	MOVD	24(RSP), R0
	0x0034 00052 (str_atom.go:12)	MOVD	R0, "".ch-56(SP)
	0x0038 00056 (str_atom.go:14)	MOVW	ZR, 8(RSP)
	0x003c 00060 (str_atom.go:14)	MOVD	$"".main.func1·f(SB), R1
	0x0044 00068 (str_atom.go:14)	MOVD	R1, 16(RSP)
	0x0048 00072 (str_atom.go:14)	PCDATA	$1, $1
	0x0048 00072 (str_atom.go:14)	CALL	runtime.newproc(SB)
	0x004c 00076 (str_atom.go:30)	MOVD	$8, R0
	0x0050 00080 (str_atom.go:30)	MOVW	R0, 8(RSP)
	0x0054 00084 (str_atom.go:30)	MOVD	$"".main.func2·f(SB), R0
	0x005c 00092 (str_atom.go:30)	MOVD	R0, 16(RSP)
	0x0060 00096 (str_atom.go:30)	MOVD	"".ch-56(SP), R0
	0x0064 00100 (str_atom.go:30)	MOVD	R0, 24(RSP)
	0x0068 00104 (str_atom.go:30)	CALL	runtime.newproc(SB)
	0x006c 00108 (str_atom.go:30)	MOVD	ZR, R0
	0x0070 00112 (str_atom.go:39)	JMP	268
	0x0074 00116 (str_atom.go:39)	MOVD	R0, "".i-64(SP)
	0x0078 00120 (str_atom.go:40)	STP	(ZR, ZR), ""..autotmp_9-48(SP)
	0x007c 00124 (str_atom.go:40)	MOVD	"".ch-56(SP), R0
	0x0080 00128 (str_atom.go:40)	MOVD	R0, 8(RSP)
	0x0084 00132 (str_atom.go:40)	MOVD	$""..autotmp_9-48(SP), R1
	0x0088 00136 (str_atom.go:40)	MOVD	R1, 16(RSP)
	0x008c 00140 (str_atom.go:40)	PCDATA	$1, $2
	0x008c 00140 (str_atom.go:40)	CALL	runtime.chanrecv1(SB)
	0x0090 00144 (str_atom.go:40)	MOVD	""..autotmp_9-48(SP), R0
	0x0094 00148 (str_atom.go:40)	MOVD	""..autotmp_9-40(SP), R1
	0x0098 00152 (str_atom.go:40)	MOVD	R0, 8(RSP)
	0x009c 00156 (str_atom.go:40)	MOVD	R1, 16(RSP)
	0x00a0 00160 (str_atom.go:40)	PCDATA	$1, $1
	0x00a0 00160 (str_atom.go:40)	CALL	runtime.convTstring(SB)
	0x00a4 00164 (str_atom.go:40)	MOVD	24(RSP), R0
	0x00a8 00168 (str_atom.go:40)	STP	(ZR, ZR), ""..autotmp_14-32(SP)
	0x00ac 00172 (str_atom.go:40)	STP	(ZR, ZR), ""..autotmp_14-16(SP)
	0x00b0 00176 (str_atom.go:40)	MOVD	$type.string(SB), R1
	0x00b8 00184 (str_atom.go:40)	MOVD	R1, ""..autotmp_14-32(SP)
	0x00bc 00188 (str_atom.go:40)	MOVD	$""..stmp_0(SB), R2
	0x00c4 00196 (str_atom.go:40)	MOVD	R2, ""..autotmp_14-24(SP)
	0x00c8 00200 (str_atom.go:40)	MOVD	R1, ""..autotmp_14-16(SP)
	0x00cc 00204 (str_atom.go:40)	MOVD	R0, ""..autotmp_14-8(SP)
	0x00d0 00208 (<unknown line number>)	NOP
	0x00d0 00208 (<unknown line number>)	PCDATA	$0, $-3
	0x00d0 00208 (str_atom.go:40)	MOVD	os.Stdout(SB), R0
	0x00dc 00220 (str_atom.go:40)	PCDATA	$0, $-1
	0x00dc 00220 (str_atom.go:40)	MOVD	$go.itab.*os.File,io.Writer(SB), R3
	0x00e4 00228 (str_atom.go:40)	MOVD	R3, 8(RSP)
	0x00e8 00232 (str_atom.go:40)	MOVD	R0, 16(RSP)
	0x00ec 00236 (str_atom.go:40)	MOVD	$""..autotmp_14-32(SP), R0
	0x00f0 00240 (str_atom.go:40)	MOVD	R0, 24(RSP)
	0x00f4 00244 (str_atom.go:40)	MOVD	$2, R0
	0x00f8 00248 (str_atom.go:40)	MOVD	R0, 32(RSP)
	0x00fc 00252 (str_atom.go:40)	MOVD	R0, 40(RSP)
	0x0100 00256 (str_atom.go:40)	CALL	fmt.Fprintln(SB)
	0x0104 00260 (str_atom.go:39)	MOVD	"".i-64(SP), R0
	0x0108 00264 (str_atom.go:39)	ADD	$1, R0, R0
	0x010c 00268 (str_atom.go:39)	CMP	$10, R0
	0x0110 00272 (str_atom.go:39)	BLT	116
	0x0114 00276 (str_atom.go:43)	PCDATA	$1, $-1
	0x0114 00276 (str_atom.go:43)	MOVD	-8(RSP), R29
	0x0118 00280 (str_atom.go:43)	MOVD.P	144(RSP), R30
	0x011c 00284 (str_atom.go:43)	RET	(R30)
	0x0120 00288 (str_atom.go:43)	NOP
	0x0120 00288 (str_atom.go:10)	PCDATA	$1, $-1
	0x0120 00288 (str_atom.go:10)	PCDATA	$0, $-2
	0x0120 00288 (str_atom.go:10)	MOVD	R30, R3
	0x0124 00292 (str_atom.go:10)	CALL	runtime.morestack_noctxt(SB)
	0x0128 00296 (str_atom.go:10)	PCDATA	$0, $-1
	0x0128 00296 (str_atom.go:10)	JMP	0
	0x0000 81 0b 40 f9 e2 43 00 d1 5f 00 01 eb a9 08 00 54  ..@..C.._......T
	0x0010 fe 0f 17 f8 fd 83 1f f8 fd 23 00 d1 00 00 00 90  .........#......
	0x0020 00 00 00 91 e0 07 00 f9 ff 0b 00 f9 00 00 00 94  ................
	0x0030 e0 0f 40 f9 e0 2b 00 f9 ff 0b 00 b9 01 00 00 90  ..@..+..........
	0x0040 21 00 00 91 e1 0b 00 f9 00 00 00 94 e0 03 7d b2  !.............}.
	0x0050 e0 0b 00 b9 00 00 00 90 00 00 00 91 e0 0b 00 f9  ................
	0x0060 e0 2b 40 f9 e0 0f 00 f9 00 00 00 94 00 00 80 d2  .+@.............
	0x0070 27 00 00 14 e0 27 00 f9 ff ff 05 a9 e0 2b 40 f9  '....'.......+@.
	0x0080 e0 07 00 f9 e1 63 01 91 e1 0b 00 f9 00 00 00 94  .....c..........
	0x0090 e0 2f 40 f9 e1 33 40 f9 e0 07 00 f9 e1 0b 00 f9  ./@..3@.........
	0x00a0 00 00 00 94 e0 0f 40 f9 ff ff 06 a9 ff ff 07 a9  ......@.........
	0x00b0 01 00 00 90 21 00 00 91 e1 37 00 f9 02 00 00 90  ....!....7......
	0x00c0 42 00 00 91 e2 3b 00 f9 e1 3f 00 f9 e0 43 00 f9  B....;...?...C..
	0x00d0 1b 00 00 90 7b 03 00 91 60 03 40 f9 03 00 00 90  ....{...`.@.....
	0x00e0 63 00 00 91 e3 07 00 f9 e0 0b 00 f9 e0 a3 01 91  c...............
	0x00f0 e0 0f 00 f9 e0 03 7f b2 e0 13 00 f9 e0 17 00 f9  ................
	0x0100 00 00 00 94 e0 27 40 f9 00 04 00 91 1f 28 00 f1  .....'@......(..
	0x0110 2b fb ff 54 fd 83 5f f8 fe 07 49 f8 c0 03 5f d6  +..T.._...I..._.
	0x0120 e3 03 1e aa 00 00 00 94 b6 ff ff 17 00 00 00 00  ................
	rel 0+0 t=24 type.string<0>+0
	rel 0+0 t=24 type.string<0>+0
	rel 0+0 t=24 type.*os.File<0>+0
	rel 28+8 t=3 type.chan string<0>+0
	rel 44+4 t=9 runtime.makechan<1>+0
	rel 60+8 t=3 "".main.func1·f<0>+0
	rel 72+4 t=9 runtime.newproc<1>+0
	rel 84+8 t=3 "".main.func2·f<0>+0
	rel 104+4 t=9 runtime.newproc<1>+0
	rel 140+4 t=9 runtime.chanrecv1<1>+0
	rel 160+4 t=9 runtime.convTstring<1>+0
	rel 176+8 t=3 type.string<0>+0
	rel 188+8 t=3 ""..stmp_0<0>+0
	rel 208+8 t=3 os.Stdout<0>+0
	rel 220+8 t=3 go.itab.*os.File,io.Writer<0>+0
	rel 256+4 t=9 fmt.Fprintln<1>+0
	rel 292+4 t=9 runtime.morestack_noctxt<0>+0
"".main.func2<1> STEXT size=144 args=0x8 locals=0x28 funcid=0x0
	0x0000 00000 (str_atom.go:30)	TEXT	"".main.func2(SB), ABIInternal, $48-8
	0x0000 00000 (str_atom.go:30)	MOVD	16(g), R1
	0x0004 00004 (str_atom.go:30)	PCDATA	$0, $-2
	0x0004 00004 (str_atom.go:30)	MOVD	RSP, R2
	0x0008 00008 (str_atom.go:30)	CMP	R1, R2
	0x000c 00012 (str_atom.go:30)	BLS	128
	0x0010 00016 (str_atom.go:30)	PCDATA	$0, $-1
	0x0010 00016 (str_atom.go:30)	MOVD.W	R30, -48(RSP)
	0x0014 00020 (str_atom.go:30)	MOVD	R29, -8(RSP)
	0x0018 00024 (str_atom.go:30)	SUB	$8, RSP, R29
	0x001c 00028 (str_atom.go:30)	FUNCDATA	ZR, gclocals·1a65e721a2ccc325b382662e7ffee780(SB)
	0x001c 00028 (str_atom.go:30)	FUNCDATA	$1, gclocals·2589ca35330fc0fce83503f4569854a0(SB)
	0x001c 00028 (str_atom.go:30)	FUNCDATA	$2, "".main.func2.stkobj(SB)
	0x001c 00028 (str_atom.go:30)	FUNCDATA	$5, "".main.func2.arginfo1(SB)
	0x001c 00028 (str_atom.go:30)	PCDATA	$0, $-3
	0x001c 00028 (str_atom.go:32)	MOVD	"".a(SB), R0
	0x0028 00040 (str_atom.go:32)	PCDATA	$0, $-4
	0x0028 00040 (str_atom.go:32)	MOVD	"".a+8(SB), R1
	0x0034 00052 (str_atom.go:32)	PCDATA	$0, $-1
	0x0034 00052 (str_atom.go:33)	CMP	$1, R1
	0x0038 00056 (str_atom.go:33)	BNE	72
	0x003c 00060 (str_atom.go:33)	MOVBU	(R0), R2
	0x0040 00064 (str_atom.go:33)	CMPW	$206158430256, R2
	0x0044 00068 (str_atom.go:33)	BEQ	28
	0x0048 00072 (str_atom.go:33)	CMP	$2, R1
	0x004c 00076 (str_atom.go:33)	BNE	96
	0x0050 00080 (str_atom.go:33)	MOVHU	(R0), R2
	0x0054 00084 (str_atom.go:33)	PCDATA	$0, $-3
	0x0054 00084 (str_atom.go:33)	CMPW	$107069239746913, R2
	0x005c 00092 (str_atom.go:33)	PCDATA	$0, $-1
	0x005c 00092 (str_atom.go:33)	BEQ	28
	0x0060 00096 (str_atom.go:34)	MOVD	R0, ""..autotmp_3-16(SP)
	0x0064 00100 (str_atom.go:34)	MOVD	R1, ""..autotmp_3-8(SP)
	0x0068 00104 (str_atom.go:34)	MOVD	"".ch(FP), R0
	0x006c 00108 (str_atom.go:34)	MOVD	R0, 8(RSP)
	0x0070 00112 (str_atom.go:34)	MOVD	$""..autotmp_3-16(SP), R1
	0x0074 00116 (str_atom.go:34)	MOVD	R1, 16(RSP)
	0x0078 00120 (str_atom.go:34)	PCDATA	$1, ZR
	0x0078 00120 (str_atom.go:34)	CALL	runtime.chansend1(SB)
	0x007c 00124 (str_atom.go:34)	JMP	28
	0x0080 00128 (str_atom.go:34)	NOP
	0x0080 00128 (str_atom.go:30)	PCDATA	$1, $-1
	0x0080 00128 (str_atom.go:30)	PCDATA	$0, $-2
	0x0080 00128 (str_atom.go:30)	MOVD	R30, R3
	0x0084 00132 (str_atom.go:30)	CALL	runtime.morestack_noctxt(SB)
	0x0088 00136 (str_atom.go:30)	PCDATA	$0, $-1
	0x0088 00136 (str_atom.go:30)	JMP	0
	0x0000 81 0b 40 f9 e2 03 00 91 5f 00 01 eb a9 03 00 54  ..@....._......T
	0x0010 fe 0f 1d f8 fd 83 1f f8 fd 23 00 d1 1b 00 00 90  .........#......
	0x0020 7b 03 00 91 60 03 40 f9 1b 00 00 90 7b 03 00 91  {...`.@.....{...
	0x0030 61 03 40 f9 3f 04 00 f1 81 00 00 54 02 00 40 39  a.@.?......T..@9
	0x0040 5f c0 00 71 c0 fe ff 54 3f 08 00 f1 a1 00 00 54  _..q...T?......T
	0x0050 02 00 40 79 3b 2c 8c 52 5f 00 1b 6b 00 fe ff 54  ..@y;,.R_..k...T
	0x0060 e0 0f 00 f9 e1 13 00 f9 e0 1f 40 f9 e0 07 00 f9  ..........@.....
	0x0070 e1 63 00 91 e1 0b 00 f9 00 00 00 94 e8 ff ff 17  .c..............
	0x0080 e3 03 1e aa 00 00 00 94 de ff ff 17 00 00 00 00  ................
	rel 28+8 t=3 "".a<0>+0
	rel 40+8 t=3 "".a<0>+8
	rel 120+4 t=9 runtime.chansend1<1>+0
	rel 132+4 t=9 runtime.morestack_noctxt<0>+0
"".main.func1<1> STEXT size=240 args=0x0 locals=0x18 funcid=0x0
	0x0000 00000 (str_atom.go:14)	TEXT	"".main.func1(SB), ABIInternal, $32-0
	0x0000 00000 (str_atom.go:14)	MOVD	16(g), R1
	0x0004 00004 (str_atom.go:14)	PCDATA	$0, $-2
	0x0004 00004 (str_atom.go:14)	MOVD	RSP, R2
	0x0008 00008 (str_atom.go:14)	CMP	R1, R2
	0x000c 00012 (str_atom.go:14)	BLS	228
	0x0010 00016 (str_atom.go:14)	PCDATA	$0, $-1
	0x0010 00016 (str_atom.go:14)	MOVD.W	R30, -32(RSP)
	0x0014 00020 (str_atom.go:14)	MOVD	R29, -8(RSP)
	0x0018 00024 (str_atom.go:14)	SUB	$8, RSP, R29
	0x001c 00028 (str_atom.go:14)	FUNCDATA	ZR, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001c 00028 (str_atom.go:14)	FUNCDATA	$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
	0x001c 00028 (str_atom.go:14)	MOVD	$1, R0
	0x0020 00032 (str_atom.go:17)	JMP	60
	0x0024 00036 (str_atom.go:25)	MOVD	$1000000, R0
	0x002c 00044 (str_atom.go:25)	MOVD	R0, 8(RSP)
	0x0030 00048 (str_atom.go:25)	PCDATA	$1, ZR
	0x0030 00048 (str_atom.go:25)	CALL	time.Sleep(SB)
	0x0034 00052 (str_atom.go:26)	MOVD	"".i-8(SP), R0
	0x0038 00056 (str_atom.go:26)	ADD	$1, R0, R0
	0x003c 00060 (str_atom.go:19)	MOVD	R0, "".i-8(SP)
	0x0040 00064 (str_atom.go:19)	TBNZ	ZR, R0, 148
	0x0044 00068 (str_atom.go:20)	MOVD	$1, R1
	0x0048 00072 (str_atom.go:20)	PCDATA	$0, $-3
	0x0048 00072 (str_atom.go:20)	MOVD	R1, "".a+8(SB)
	0x0054 00084 (str_atom.go:20)	PCDATA	$0, $-1
	0x0054 00084 (str_atom.go:20)	PCDATA	ZR, $-2
	0x0054 00084 (str_atom.go:20)	MOVWU	runtime.writeBarrier(SB), R4
	0x0060 00096 (str_atom.go:20)	CBNZW	R4, 124
	0x0064 00100 (str_atom.go:20)	MOVD	$go.string."0"(SB), R2
	0x006c 00108 (str_atom.go:20)	MOVD	R2, "".a(SB)
	0x0078 00120 (str_atom.go:20)	JMP	36
	0x007c 00124 (str_atom.go:20)	MOVD	$"".a(SB), R2
	0x0084 00132 (str_atom.go:20)	MOVD	$go.string."0"(SB), R3
	0x008c 00140 (str_atom.go:20)	CALL	runtime.gcWriteBarrier(SB)
	0x0090 00144 (str_atom.go:20)	JMP	36
	0x0094 00148 (str_atom.go:22)	PCDATA	ZR, $-1
	0x0094 00148 (str_atom.go:22)	MOVD	$2, R1
	0x0098 00152 (str_atom.go:22)	PCDATA	$0, $-4
	0x0098 00152 (str_atom.go:22)	MOVD	R1, "".a+8(SB)
	0x00a4 00164 (str_atom.go:22)	PCDATA	$0, $-1
	0x00a4 00164 (str_atom.go:22)	PCDATA	ZR, $-2
	0x00a4 00164 (str_atom.go:22)	MOVWU	runtime.writeBarrier(SB), R4
	0x00b0 00176 (str_atom.go:22)	CBNZW	R4, 204
	0x00b4 00180 (str_atom.go:22)	MOVD	$go.string."aa"(SB), R2
	0x00bc 00188 (str_atom.go:22)	MOVD	R2, "".a(SB)
	0x00c8 00200 (str_atom.go:22)	JMP	36
	0x00cc 00204 (str_atom.go:22)	MOVD	$"".a(SB), R2
	0x00d4 00212 (str_atom.go:22)	MOVD	$go.string."aa"(SB), R3
	0x00dc 00220 (str_atom.go:22)	CALL	runtime.gcWriteBarrier(SB)
	0x00e0 00224 (str_atom.go:22)	JMP	36
	0x00e4 00228 (str_atom.go:22)	NOP
	0x00e4 00228 (str_atom.go:14)	PCDATA	$1, $-1
	0x00e4 00228 (str_atom.go:14)	PCDATA	$0, $-2
	0x00e4 00228 (str_atom.go:14)	MOVD	R30, R3
	0x00e8 00232 (str_atom.go:14)	CALL	runtime.morestack_noctxt(SB)
	0x00ec 00236 (str_atom.go:14)	PCDATA	$0, $-1
	0x00ec 00236 (str_atom.go:14)	JMP	0
	0x0000 81 0b 40 f9 e2 03 00 91 5f 00 01 eb c9 06 00 54  ..@....._......T
	0x0010 fe 0f 1e f8 fd 83 1f f8 fd 23 00 d1 e0 03 40 b2  .........#....@.
	0x0020 07 00 00 14 00 48 88 d2 e0 01 a0 f2 e0 07 00 f9  .....H..........
	0x0030 00 00 00 94 e0 0b 40 f9 00 04 00 91 e0 0b 00 f9  ......@.........
	0x0040 a0 02 00 37 e1 03 40 b2 1b 00 00 90 7b 03 00 91  ...7..@.....{...
	0x0050 61 03 00 f9 1b 00 00 90 7b 03 00 91 64 03 40 b9  a.......{...d.@.
	0x0060 e4 00 00 35 02 00 00 90 42 00 00 91 1b 00 00 90  ...5....B.......
	0x0070 7b 03 00 91 62 03 00 f9 eb ff ff 17 02 00 00 90  {...b...........
	0x0080 42 00 00 91 03 00 00 90 63 00 00 91 00 00 00 94  B.......c.......
	0x0090 e5 ff ff 17 e1 03 7f b2 1b 00 00 90 7b 03 00 91  ............{...
	0x00a0 61 03 00 f9 1b 00 00 90 7b 03 00 91 64 03 40 b9  a.......{...d.@.
	0x00b0 e4 00 00 35 02 00 00 90 42 00 00 91 1b 00 00 90  ...5....B.......
	0x00c0 7b 03 00 91 62 03 00 f9 d7 ff ff 17 02 00 00 90  {...b...........
	0x00d0 42 00 00 91 03 00 00 90 63 00 00 91 00 00 00 94  B.......c.......
	0x00e0 d1 ff ff 17 e3 03 1e aa 00 00 00 94 c5 ff ff 17  ................
	rel 48+4 t=9 time.Sleep<1>+0
	rel 72+8 t=3 "".a<0>+8
	rel 84+8 t=3 runtime.writeBarrier<0>+0
	rel 100+8 t=3 go.string."0"<0>+0
	rel 108+8 t=3 "".a<0>+0
	rel 124+8 t=3 "".a<0>+0
	rel 132+8 t=3 go.string."0"<0>+0
	rel 140+4 t=9 runtime.gcWriteBarrier<1>+0
	rel 152+8 t=3 "".a<0>+8
	rel 164+8 t=3 runtime.writeBarrier<0>+0
	rel 180+8 t=3 go.string."aa"<0>+0
	rel 188+8 t=3 "".a<0>+0
	rel 204+8 t=3 "".a<0>+0
	rel 212+8 t=3 go.string."aa"<0>+0
	rel 220+4 t=9 runtime.gcWriteBarrier<1>+0
	rel 232+4 t=9 runtime.morestack_noctxt<0>+0
os.(*File).close<1> STEXT dupok size=32 args=0x18 locals=0x0 funcid=0x0 leaf
	0x0000 00000 (<autogenerated>:1)	TEXT	os.(*File).close(SB), DUPOK|LEAF|NOFRAME|ABIInternal, $0-24
	0x0000 00000 (<autogenerated>:1)	FUNCDATA	ZR, gclocals·e6397a44f8e1b6e77d0f200b4fba5269(SB)
	0x0000 00000 (<autogenerated>:1)	FUNCDATA	$1, gclocals·69c1753bd5f81501d95132d08af04464(SB)
	0x0000 00000 (<autogenerated>:1)	FUNCDATA	$5, os.(*File).close.arginfo1(SB)
	0x0000 00000 (<autogenerated>:1)	MOVD	""..this(FP), R0
	0x0004 00004 (<autogenerated>:1)	MOVD	(R0), R0
	0x0008 00008 (<autogenerated>:1)	MOVD	R0, ""..this(FP)
	0x000c 00012 (<autogenerated>:1)	STP	(ZR, ZR), "".~r0+8(FP)
	0x0010 00016 (<autogenerated>:1)	JMP	os.(*file).close(SB)
	0x0000 e0 07 40 f9 00 00 40 f9 e0 07 00 f9 ff 7f 01 a9  ..@...@.........
	0x0010 00 00 00 14 00 00 00 00 00 00 00 00 00 00 00 00  ................
	rel 16+4 t=9 os.(*file).close<1>+0
go.cuinfo.packagename.<0> SDWARFCUINFO dupok size=0
	0x0000 6d 61 69 6e                                      main
go.string."0"<0> SRODATA dupok size=1
	0x0000 30                                               0
""..inittask<0> SNOPTRDATA size=40
	0x0000 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00  ................
	0x0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0020 00 00 00 00 00 00 00 00                          ........
	rel 24+8 t=1 fmt..inittask<0>+0
	rel 32+8 t=1 time..inittask<0>+0
go.info.fmt.Println$abstract<0> SDWARFABSFCN dupok size=42
	0x0000 04 66 6d 74 2e 50 72 69 6e 74 6c 6e 00 01 01 11  .fmt.Println....
	0x0010 61 00 00 00 00 00 00 11 6e 00 01 00 00 00 00 11  a.......n.......
	0x0020 65 72 72 00 01 00 00 00 00 00                    err.......
	rel 0+0 t=23 type.[]interface {}<0>+0
	rel 0+0 t=23 type.error<0>+0
	rel 0+0 t=23 type.int<0>+0
	rel 19+4 t=31 go.info.[]interface {}<0>+0
	rel 27+4 t=31 go.info.int<0>+0
	rel 37+4 t=31 go.info.error<0>+0
go.string."Got strange string: "<0> SRODATA dupok size=20
	0x0000 47 6f 74 20 73 74 72 61 6e 67 65 20 73 74 72 69  Got strange stri
	0x0010 6e 67 3a 20                                      ng: 
go.string."aa"<0> SRODATA dupok size=2
	0x0000 61 61                                            aa
"".a<0> SDATA size=16
	0x0000 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
	rel 0+8 t=1 go.string."0"<0>+0
""..stmp_0<0> SRODATA static size=16
	0x0000 00 00 00 00 00 00 00 00 14 00 00 00 00 00 00 00  ................
	rel 0+8 t=1 go.string."Got strange string: "<0>+0
runtime.nilinterequal·f<0> SRODATA dupok size=8
	0x0000 00 00 00 00 00 00 00 00                          ........
	rel 0+8 t=1 runtime.nilinterequal<1>+0
runtime.memequal64·f<0> SRODATA dupok size=8
	0x0000 00 00 00 00 00 00 00 00                          ........
	rel 0+8 t=1 runtime.memequal64<1>+0
runtime.gcbits.01<0> SRODATA dupok size=1
	0x0000 01                                               .
type..namedata.*interface {}-<0> SRODATA dupok size=15
	0x0000 00 0d 2a 69 6e 74 65 72 66 61 63 65 20 7b 7d     ..*interface {}
type.*interface {}<0> SRODATA dupok size=56
	0x0000 08 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
	0x0010 4f 0f 96 9d 08 08 08 36 00 00 00 00 00 00 00 00  O......6........
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00                          ........
	rel 24+8 t=1 runtime.memequal64·f<0>+0
	rel 32+8 t=1 runtime.gcbits.01<0>+0
	rel 40+4 t=5 type..namedata.*interface {}-<0>+0
	rel 48+8 t=1 type.interface {}<0>+0
runtime.gcbits.02<0> SRODATA dupok size=1
	0x0000 02                                               .
type.interface {}<0> SRODATA dupok size=80
	0x0000 10 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
	0x0010 e7 57 a0 18 02 08 08 14 00 00 00 00 00 00 00 00  .W..............
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	rel 24+8 t=1 runtime.nilinterequal·f<0>+0
	rel 32+8 t=1 runtime.gcbits.02<0>+0
	rel 40+4 t=5 type..namedata.*interface {}-<0>+0
	rel 44+4 t=-32763 type.*interface {}<0>+0
	rel 56+8 t=1 type.interface {}<0>+80
type..namedata.*[]interface {}-<0> SRODATA dupok size=17
	0x0000 00 0f 2a 5b 5d 69 6e 74 65 72 66 61 63 65 20 7b  ..*[]interface {
	0x0010 7d                                               }
type.*[]interface {}<0> SRODATA dupok size=56
	0x0000 08 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
	0x0010 f3 04 9a e7 08 08 08 36 00 00 00 00 00 00 00 00  .......6........
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00                          ........
	rel 24+8 t=1 runtime.memequal64·f<0>+0
	rel 32+8 t=1 runtime.gcbits.01<0>+0
	rel 40+4 t=5 type..namedata.*[]interface {}-<0>+0
	rel 48+8 t=1 type.[]interface {}<0>+0
type.[]interface {}<0> SRODATA dupok size=56
	0x0000 18 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
	0x0010 70 93 ea 2f 02 08 08 17 00 00 00 00 00 00 00 00  p../............
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00                          ........
	rel 32+8 t=1 runtime.gcbits.01<0>+0
	rel 40+4 t=5 type..namedata.*[]interface {}-<0>+0
	rel 44+4 t=-32763 type.*[]interface {}<0>+0
	rel 48+8 t=1 type.interface {}<0>+0
type..namedata.*chan string-<0> SRODATA dupok size=14
	0x0000 00 0c 2a 63 68 61 6e 20 73 74 72 69 6e 67        ..*chan string
type.*chan string<0> SRODATA dupok size=56
	0x0000 08 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
	0x0010 f4 25 61 85 08 08 08 36 00 00 00 00 00 00 00 00  .%a....6........
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00                          ........
	rel 24+8 t=1 runtime.memequal64·f<0>+0
	rel 32+8 t=1 runtime.gcbits.01<0>+0
	rel 40+4 t=5 type..namedata.*chan string-<0>+0
	rel 48+8 t=1 type.chan string<0>+0
type.chan string<0> SRODATA dupok size=64
	0x0000 08 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
	0x0010 8d 9e 8b c9 0a 08 08 32 00 00 00 00 00 00 00 00  .......2........
	0x0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0030 00 00 00 00 00 00 00 00 03 00 00 00 00 00 00 00  ................
	rel 24+8 t=1 runtime.memequal64·f<0>+0
	rel 32+8 t=1 runtime.gcbits.01<0>+0
	rel 40+4 t=5 type..namedata.*chan string-<0>+0
	rel 44+4 t=-32763 type.*chan string<0>+0
	rel 48+8 t=1 type.string<0>+0
runtime.gcbits.0a<0> SRODATA dupok size=1
	0x0000 0a                                               .
go.itab.*os.File,io.Writer<0> SRODATA dupok size=32
	0x0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0010 44 b5 f3 33 00 00 00 00 00 00 00 00 00 00 00 00  D..3............
	rel 0+8 t=1 type.io.Writer<0>+0
	rel 8+8 t=1 type.*os.File<0>+0
	rel 24+8 t=-32767 os.(*File).Write<1>+0
type..importpath.fmt.<0> SRODATA dupok size=5
	0x0000 00 03 66 6d 74                                   ..fmt
type..importpath.time.<0> SRODATA dupok size=6
	0x0000 00 04 74 69 6d 65                                ..time
"".main.func1·f<0> SRODATA dupok size=8
	0x0000 00 00 00 00 00 00 00 00                          ........
	rel 0+8 t=1 "".main.func1<1>+0
"".main.func2·f<0> SRODATA dupok size=8
	0x0000 00 00 00 00 00 00 00 00                          ........
	rel 0+8 t=1 "".main.func2<1>+0
gclocals·7d2d5fca80364273fb07d5820a76fef4<0> SRODATA dupok size=8
	0x0000 03 00 00 00 00 00 00 00                          ........
gclocals·1373f50311b358236be33e875131d17d<0> SRODATA dupok size=11
	0x0000 03 00 00 00 07 00 00 00 00 01 03                 ...........
"".main.stkobj<0> SRODATA static size=56
	0x0000 02 00 00 00 00 00 00 00 d0 ff ff ff 10 00 00 00  ................
	0x0010 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	0x0020 e0 ff ff ff 20 00 00 00 20 00 00 00 00 00 00 00  .... ... .......
	0x0030 00 00 00 00 00 00 00 00                          ........
	rel 24+8 t=1 runtime.gcbits.01<0>+0
	rel 48+8 t=1 runtime.gcbits.0a<0>+0
gclocals·1a65e721a2ccc325b382662e7ffee780<0> SRODATA dupok size=10
	0x0000 02 00 00 00 01 00 00 00 01 00                    ..........
gclocals·2589ca35330fc0fce83503f4569854a0<0> SRODATA dupok size=10
	0x0000 02 00 00 00 02 00 00 00 00 00                    ..........
"".main.func2.stkobj<0> SRODATA static size=32
	0x0000 01 00 00 00 00 00 00 00 f0 ff ff ff 10 00 00 00  ................
	0x0010 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	rel 24+8 t=1 runtime.gcbits.01<0>+0
"".main.func2.arginfo1<0> SRODATA static dupok size=3
	0x0000 00 08 ff                                         ...
gclocals·33cdeccccebe80329f1fdbee7f5874cb<0> SRODATA dupok size=8
	0x0000 01 00 00 00 00 00 00 00                          ........
gclocals·e6397a44f8e1b6e77d0f200b4fba5269<0> SRODATA dupok size=10
	0x0000 02 00 00 00 03 00 00 00 01 00                    ..........
gclocals·69c1753bd5f81501d95132d08af04464<0> SRODATA dupok size=8
	0x0000 02 00 00 00 00 00 00 00                          ........
os.(*File).close.arginfo1<0> SRODATA static dupok size=3
	0x0000 00 08 ff                                         ...



参考:

Golang string变量操作的原子性

go 字符串string的并发读写的一个坑

golang: 常用数据类型底层结构分析

你不知道的 Go 之 string

更多相关:

golang 中 int加一是原子性吗

golang int并发安全 atom

姊妹篇:

golang之map并发访问

golang之slice并发访问



str="aa",len=1,变为”a”容易理解,但str="0",len=2为什么会是”05”呢?


string在底层的存储方式如下：

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type StringHeader struct {
	Data uintptr // 内容的指针地址
	Len  int     // 长度
}

在上面的并发读写过程中，即发生了

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s1 := StringHeader{
	Data: `指向"aa"的那个内存地址，记为x`,
	Len: 1,
}

s2 := StringHeader{
	Data: `指向"0"的那个内存地址，记为y`,
	Len: 2,
}

可以打印出y的内容，就一目了然了


先看如下例子：

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package main

import (
	"encoding/hex"
	"fmt"
	"strings"
	"unsafe"
)

func main() {

	demoStr := "abcdefghijklmnop1234567887654321"
	dump("demoStr", &demoStr)

}

func dump(name string, strPtr *string) {
	// 分隔符
	fmt.Println(strings.Repeat("-", 30))

	// 打印strPtr这个指针类型的变量的内存地址
	fmt.Printf("&%s:%p\n", name, strPtr)
	// 强制转换为16字节的byte数组 （*[0x10]byte)(unsafe.Pointer(strPtr)），是个指针类型。再用*取指针内容； 然后将数组转为切片，[:]
	fmt.Println(hex.Dump((*(*[0x10]byte)(unsafe.Pointer(strPtr)))[:]))

	// 获取上面这个指针所指向的内存地址
	p := *(*int)(unsafe.Pointer(strPtr)) // 当成int型(需要C经验更好理解)
	fmt.Printf("%s:0x%x\n", name, p)
	fmt.Println(hex.Dump((*(*[0x20]byte)(unsafe.Pointer(uintptr(p))))[:]))

}

输出为:

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7
------------------------------
&demoStr:0x14000010240
00000000  82 34 ea 00 01 00 00 00  20 00 00 00 00 00 00 00  |.4...... .......|

demoStr:0x100ea3482
00000000  61 62 63 64 65 66 67 68  69 6a 6b 6c 6d 6e 6f 70  |abcdefghijklmnop|
00000010  31 32 33 34 35 36 37 38  38 37 36 35 34 33 32 31  |1234567887654321|

（内存地址对应的内容也是16进制格式）

比对ASCII码表，

可以看出一一对应


而对于”0”:

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package main

import (
	"encoding/hex"
	"fmt"
	"strings"
	"unsafe"
)

func main() {

	demoStr := "0"
	dump("demoStr", &demoStr)

}

func dump(name string, strPtr *string) {
	// 分隔符
	fmt.Println(strings.Repeat("-", 30))

	// 打印strPtr这个指针类型的变量的内存地址
	fmt.Printf("&%s:%p\n", name, strPtr)
	// 强制转换为16字节的byte数组 （*[0x10]byte)(unsafe.Pointer(strPtr)），是个指针类型。再用*取指针内容； 然后将数组转为切片，[:]
	fmt.Println(hex.Dump((*(*[0x10]byte)(unsafe.Pointer(strPtr)))[:]))

	// 获取上面这个指针所指向的内存地址
	p := *(*int)(unsafe.Pointer(strPtr)) // 当成int型(需要C经验更好理解)
	fmt.Printf("%s:0x%x\n", name, p)
	fmt.Println(hex.Dump((*(*[0x20]byte)(unsafe.Pointer(uintptr(p))))[:]))

}

输出：

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------------------------------
&demoStr:0x14000110060
00000000  a7 a6 d1 02 01 00 00 00  01 00 00 00 00 00 00 00  |................|

demoStr:0x102d1a6a7
00000000  30 3a 3c 3d 3e 43 4c 4d  50 53 55 5a 5b 5d 5f 60  |0:<=>CLMPSUZ[]_`|
00000010  68 6d 73 7b 7d 20 2b 20  40 20 50 20 5b 25 21 28  |hms{} + @ P [%!(|

可以看出，当长度为2，但实际存的内容为1时是咋填充的

在该场景下，对于Mac，会填充为0x3a，即对应:

对于Linux，则会填充0x35,即对应5