go - 使用 cgo 时是否会发生数据竞争？

Question

Goroutines 在 cgo 和 go 的不同堆栈中运行：

C 对 Go 的调用约定或可增长堆栈一无所知，因此对 C 代码的调用必须记录 goroutine 堆栈的所有细节，切换到 C 堆栈，并运行不知道如何调用的 C 代码，或者负责程序的更大的 Go 运行时。

是否有可能触发它们之间共享的变量或类型的数据竞争？

最近，我在初始化切片时遇到错误，例如：

package controlcan

import "C"

cReceive := make([]C.struct__CAN_OBJ, 2500)

或者

package main

import "controlcan"

pReceive := make([]controlcan.CanObj, 2500)

他们俩都随机抱怨“意外故障地址”错误：

unexpected fault address 0xffffffffffffffff
fatal error: fault
[signal 0xc0000005 code=0x0 addr=0xffffffffffffffff pc=0x41c65d]

goroutine 41 [running]:
runtime.throw(0xcc969a, 0x5)
        /usr/local/go/src/runtime/panic.go:619 +0x88 fp=0xc0428ffb38 sp=0xc0428ffb18 pc=0x42d0b8
runtime.sigpanic()
        /usr/local/go/src/runtime/signal_windows.go:170 +0x13a fp=0xc0428ffb68 sp=0xc0428ffb38 pc=0x43fcca
runtime.gcMarkRootPrepare()
        /usr/local/go/src/runtime/mgcmark.go:72 +0x5d fp=0xc0428ffb70 sp=0xc0428ffb68 pc=0x41c65d
runtime.gcStart(0x0, 0x1, 0x0, 0x0)
        /usr/local/go/src/runtime/mgc.go:1350 +0x30f fp=0xc0428ffba0 sp=0xc0428ffb70 pc=0x419b6f
runtime.mallocgc(0x10000, 0xc54660, 0xc0422ee001, 0xc0423ded60)
        /usr/local/go/src/runtime/malloc.go:803 +0x448 fp=0xc0428ffc40 sp=0xc0428ffba0 pc=0x411c48
runtime.makeslice(0xc54660, 0x9c4, 0x9c4, 0xc04202ce00, 0xc04202c000, 0x411b23)
        /usr/local/go/src/runtime/slice.go:61 +0x7e fp=0xc0428ffc70 sp=0xc0428ffc40 pc=0x43fffe
controlcan.Receive(0x4, 0x0, 0x0, 0xc04267e000, 0x9c4, 0x9c4, 0x64, 0x0, 0x0, 0x0)
        /media/sf_GOPATH0/src/controlcan/controlcan.go:262 +0x75 fp=0xc0428ffd70 sp=0xc0428ffc70 pc=0xa0d795
posam/protocol/usbcan.(*Channel).receive(0xc04229d490)
        /media/sf_GOPATH0/src/posam/protocol/usbcan/usbcan.go:469 +0x536 fp=0xc0428fffd8 sp=0xc0428ffd70 pc=0xa10926
runtime.goexit()
        /usr/local/go/src/runtime/asm_amd64.s:2361 +0x1 fp=0xc0428fffe0 sp=0xc0428fffd8 pc=0x457531
created by posam/protocol/usbcan.(*Channel).Start
        /media/sf_GOPATH0/src/posam/protocol/usbcan/usbcan.go:242 +0x3aa

更新

controlcan是一个包装器包，它将定义在Golang 友好的函数.dll或库中的函数封装起来，例如，向 CAN 设备发送消息或从 CAN 设备接收消息。.soIMO，在controlcan包内和其他包中导入切片初始化语句的数据竞争真的很奇怪。

在Receive函数中，第一行声明了一个切片cReceive，如上所述，我随机得到了错误。我认为原因unexpected fault address是数据竞争而不是内存损坏，但这里需要的资源只是类型C.struct__VCI_CAN_OBJ，而不是任何变量。我希望我错了。

更糟糕的是，CanObj在其他包中使用的 typeusbcan.go仍然可能触发错误，例如pReceive. 以前，我怀疑原因可能是 的常数2500，因为原始语句是cReceive := make([]C.struct__VCI_CAN_OBJ, FRAME_LENGTH_OF_RECEPTION)。但是当我2500直接将其更改为时，错误仍然发生。

controlcan.go

package controlcan

import "C"
import (
    "fmt"
    "runtime"
    "unsafe"
)

const (
    FRAME_LENGTH_OF_RECEPTION = 2500
)

type CanObj struct { // <- accessable for other packages/goroutines
    ID         int
    TimeStamp  int
    TimeFlag   int
    SendType   byte
    RemoteFlag byte
    ExternFlag byte
    DataLen    byte
    Data       [8]byte
    Reserved   [3]byte
}

func Receive(
    devType int,
    devIndex int,
    canIndex int,
    pReceive []CanObj,
    waitTime int,
) (count int, err error) {
    cReceive := make([]C.struct__VCI_CAN_OBJ, 2500) // unexpected fault address
    cCount := C.VCI_Receive(
        C.uint(devType),
        C.uint(devIndex),
        C.uint(canIndex),
        (*C.struct__VCI_CAN_OBJ)(unsafe.Pointer(&cReceive)),
        C.uint(FRAME_LENGTH_OF_RECEPTION),
        C.int(waitTime),
    )

    // ...
}

usbcan.go

package usbcan

import "controlcan"

func (c *Channel) receive() {
    ticker := time.NewTicker(100 * time.Millisecond)
    defer ticker.Stop()
    for _ = range ticker.C {
        pReceive := make([]controlcan.CanObj, 2500) // unexpected fault address
        count, err := controlcan.Receive(
            c.DevType,
            c.DevIndex,
            c.CanIndex,
            pReceive,
            100,
        )
    // ...

更新 2：

我将cReceive创建从 Go 移动到 Cgo，从Kenny Grant窃取，并且 line 的 make-slice 错误cReceive得到解决。

package controlcan

// static VCI_CAN_OBJ** makeCanObjArray(){
//     return calloc(sizeof(VCI_CAN_OBJ*), 2500);
// }
// static void freeCanObjArray(VCI_CAN_OBJ **canObjArray){
//     int i;
//     for (i=0; i<2500;i++)
//         free(canObjArray[i]);
//     free(canObjArray);
// }
import "C"

func Receive(
    devType int,
    devIndex int,
    canIndex int,
    pReceive []CanObj,
    waitTime int,
) (count int, err error) {
    cReceive := C.makeCanObjArray()
    defer C.freeCanObjArray(cReceive)
// ...

而且我仍然无法弄清楚创建时会发生什么pReceive：

pReceive := make([]controlcan.CanObj, 2500)

unexpected fault address 0xffffffffffffffff
fatal error: fault
[signal 0xc0000005 code=0x0 addr=0xffffffffffffffff pc=0x41c65d]

goroutine 28 [running]:
runtime.throw(0xcc969a, 0x5)
        /usr/local/go/src/runtime/panic.go:619 +0x88 fp=0xc04275bc38 sp=0xc04275bc18 pc=0x42d0b8
runtime.sigpanic()
        /usr/local/go/src/runtime/signal_windows.go:170 +0x13a fp=0xc04275bc68 sp=0xc04275bc38 pc=0x43fcca
runtime.gcMarkRootPrepare()
        /usr/local/go/src/runtime/mgcmark.go:72 +0x5d fp=0xc04275bc70 sp=0xc04275bc68 pc=0x41c65d
runtime.gcStart(0x0, 0x1, 0x0, 0x0)
        /usr/local/go/src/runtime/mgc.go:1350 +0x30f fp=0xc04275bca0 sp=0xc04275bc70 pc=0x419b6f
runtime.mallocgc(0x1a000, 0xc54520, 0x1, 0xa10101)
        /usr/local/go/src/runtime/malloc.go:803 +0x448 fp=0xc04275bd40 sp=0xc04275bca0 pc=0x411c48
runtime.makeslice(0xc54520, 0x9c4, 0x9c4, 0xc0420162a0, 0x8, 0x8)
        /usr/local/go/src/runtime/slice.go:61 +0x7e fp=0xc04275bd70 sp=0xc04275bd40 pc=0x43fffe
posam/protocol/usbcan.(*Channel).receive(0xc04213fdc0)
        /media/sf_GOPATH0/src/posam/protocol/usbcan/usbcan.go:464 +0x4f0 fp=0xc04275bfd8 sp=0xc04275bd70 pc=0xa108e0
runtime.goexit()
        /usr/local/go/src/runtime/asm_amd64.s:2361 +0x1 fp=0xc04275bfe0 sp=0xc04275bfd8 pc=0x457531
created by posam/protocol/usbcan.(*Channel).Start
        /media/sf_GOPATH0/src/posam/protocol/usbcan/usbcan.go:242 +0x3aa

标签： gocan-buscgodata-race