cgo

README

Copy from go 1.17.2 runtime/cgo. In order to be compatible with lower versions

Documentation

Index

• type Handle
  • func NewHandle(v interface{}) Handle
  • func (h Handle) Delete()
  • func (h Handle) Value() interface{}

Types

type Handle

type Handle uintptr

Handle provides a way to pass values that contain Go pointers (pointers to memory allocated by Go) between Go and C without breaking the cgo pointer passing rules. A Handle is an integer value that can represent any Go value. A Handle can be passed through C and back to Go, and Go code can use the Handle to retrieve the original Go value.

The underlying type of Handle is guaranteed to fit in an integer type that is large enough to hold the bit pattern of any pointer. The zero value of a Handle is not valid, and thus is safe to use as a sentinel in C APIs.

For instance, on the Go side:

package main

/*
#include <stdint.h> // for uintptr_t

extern void MyGoPrint(uintptr_t handle);
void myprint(uintptr_t handle);
*/
import "C"
import "runtime/cgo"

//export MyGoPrint
func MyGoPrint(handle C.uintptr_t) {
	h := cgo.Handle(handle)
	val := h.Value().(string)
	println(val)
	h.Delete()
}

func main() {
	val := "hello Go"
	C.myprint(C.uintptr_t(cgo.NewHandle(val)))
	// Output: hello Go
}

and on the C side:

#include <stdint.h> // for uintptr_t

// A Go function
extern void MyGoPrint(uintptr_t handle);

// A C function
void myprint(uintptr_t handle) {
    MyGoPrint(handle);
}

func NewHandle

func NewHandle(v interface{}) Handle

NewHandle returns a handle for a given value.

The handle is valid until the program calls Delete on it. The handle uses resources, and this package assumes that C code may hold on to the handle, so a program must explicitly call Delete when the handle is no longer needed.

The intended use is to pass the returned handle to C code, which passes it back to Go, which calls Value.

func (Handle) Delete

func (h Handle) Delete()

Delete invalidates a handle. This method should only be called once the program no longer needs to pass the handle to C and the C code no longer has a copy of the handle value.

The method panics if the handle is invalid.

func (Handle) Value

func (h Handle) Value() interface{}

Value returns the associated Go value for a valid handle.

The method panics if the handle is invalid.