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pointers - 将 Go 指针传递给 Cgo

问题描述

我一直在玩 GLFW 绑定，我想通过 glfw.SetUserPointer(...) 将 Queue 结构传递给它，

因此，我这样传递它：

type CircularQueue struct {
    Values      []interface{}
    Front, Rear int32
    Capacity    int32
}

func newCircularQueue(capacity int32) *CircularQueue {
    if capacity < 1 {
        log.Fatal("Capacity of Circular Queue Zero or Negative")
    }

    queue := &CircularQueue{Capacity: capacity}
    queue.Values = make([]interface{}, capacity)
    return queue
}

...
events := newCircularQueue(16)
window.SetUserPointer(unsafe.Pointer(events))

但我得到一个运行时错误，

panic: runtime error: cgo argument has Go pointer to Go pointer

我做了一些挖掘，看起来……我引用：

Go code may pass a Go pointer to C provided the Go memory to which it 
points does not contain any Go pointers. The C code must preserve this 
property: it must not store any Go pointers in Go memory, even temporarily. 
When passing a pointer to a field in a struct, the Go memory in question is 
the memory occupied by the field, not the entire struct. When passing a 
pointer to an element in an array or slice, the Go memory in question is the 
entire array or the entire backing array of the slice.

但是，我的结构中没有指针，我很困惑:(

标签： pointersgoglfwcgo

解决方案

解决方法很简单。您必须将您提供给 C 代码的内容展平。与其传递循环队列，不如传递数据。

//C
int mysterious_c_func(const char* values, front int32_t, back int32_t, capacity int32_t);

// Go
type CircularQueue struct {
    Values      []char //this can't possibly work with interface.
    Front, Rear int32
    Capacity    int32
}
...
var q CircularQueue
data := (*C.char)(unsafe.Pointer(q.values))
C.mysterious_c_func(data, C.int(queue.Front), C.int(queue.Rear), C.int(queue.Capacity))

但真正的问题是你试图部分用 C 语言，部分用 Go 语言来实现一个复杂的数据结构。要么实现循环缓冲区

  1. 在这两种语言中，并允许从数组构造。
  2. 只有在你真正需要这个概念的地方。

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