├── LICENSE
├── README.md
├── _example
    ├── callback.h
    └── main.go
├── doc.go
└── pointer.go


/LICENSE:
--------------------------------------------------------------------------------
 1 | The MIT License (MIT)
 2 | 
 3 | Copyright (c) 2019 Yasuhiro Matsumoto
 4 | 
 5 | Permission is hereby granted, free of charge, to any person obtaining a copy
 6 | of this software and associated documentation files (the "Software"), to deal
 7 | in the Software without restriction, including without limitation the rights
 8 | to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 9 | copies of the Software, and to permit persons to whom the Software is
10 | furnished to do so, subject to the following conditions:
11 | 
12 | The above copyright notice and this permission notice shall be included in all
13 | copies or substantial portions of the Software.
14 | 
15 | THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 | IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 | FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
18 | AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 | LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
20 | OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
21 | SOFTWARE.
22 | 


--------------------------------------------------------------------------------
/README.md:
--------------------------------------------------------------------------------
 1 | # go-pointer
 2 | 
 3 | Utility for cgo
 4 | 
 5 | ## Usage
 6 | 
 7 | https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md
 8 | 
 9 | In go 1.6, cgo argument can't be passed Go pointer.
10 | 
11 | ```
12 | var s string
13 | C.pass_pointer(pointer.Save(&s))
14 | v := *(pointer.Restore(C.get_from_pointer()).(*string))
15 | ```
16 | 
17 | ## Installation
18 | 
19 | ```
20 | go get github.com/mattn/go-pointer
21 | ```
22 | 
23 | ## License
24 | 
25 | MIT
26 | 
27 | ## Author
28 | 
29 | Yasuhiro Matsumoto (a.k.a mattn)
30 | 


--------------------------------------------------------------------------------
/_example/callback.h:
--------------------------------------------------------------------------------
 1 | #include <unistd.h>
 2 | 
 3 | typedef void (*callback)(void*);
 4 | 
 5 | static void call_later(int delay, callback cb, void* data) {
 6 |   sleep(delay);
 7 |   cb(data);
 8 | }
 9 | 
10 | 


--------------------------------------------------------------------------------
/_example/main.go:
--------------------------------------------------------------------------------
 1 | package main
 2 | 
 3 | /*
 4 | #include "callback.h"
 5 | 
 6 | void call_later_go_cb(void*);
 7 | */
 8 | import "C"
 9 | import (
10 | 	"fmt"
11 | 	"unsafe"
12 | 
13 | 	"github.com/mattn/go-pointer"
14 | )
15 | 
16 | type Foo struct {
17 | 	v int
18 | }
19 | 
20 | func main() {
21 | 	f := &Foo{123}
22 | 	C.call_later(3, C.callback(C.call_later_go_cb), pointer.Save(f))
23 | }
24 | 
25 | //export call_later_go_cb
26 | func call_later_go_cb(data unsafe.Pointer) {
27 | 	f := pointer.Restore(data).(*Foo)
28 | 	fmt.Println(f.v)
29 | }
30 | 


--------------------------------------------------------------------------------
/doc.go:
--------------------------------------------------------------------------------
1 | package pointer
2 | 


--------------------------------------------------------------------------------
/pointer.go:
--------------------------------------------------------------------------------
 1 | package pointer
 2 | 
 3 | // #include <stdlib.h>
 4 | import "C"
 5 | import (
 6 | 	"sync"
 7 | 	"unsafe"
 8 | )
 9 | 
10 | var (
11 | 	mutex sync.RWMutex
12 | 	store = map[unsafe.Pointer]interface{}{}
13 | )
14 | 
15 | func Save(v interface{}) unsafe.Pointer {
16 | 	if v == nil {
17 | 		return nil
18 | 	}
19 | 
20 | 	// Generate real fake C pointer.
21 | 	// This pointer will not store any data, but will bi used for indexing purposes.
22 | 	// Since Go doest allow to cast dangling pointer to unsafe.Pointer, we do rally allocate one byte.
23 | 	// Why we need indexing, because Go doest allow C code to store pointers to Go data.
24 | 	var ptr unsafe.Pointer = C.malloc(C.size_t(1))
25 | 	if ptr == nil {
26 | 		panic("can't allocate 'cgo-pointer hack index pointer': ptr == nil")
27 | 	}
28 | 
29 | 	mutex.Lock()
30 | 	store[ptr] = v
31 | 	mutex.Unlock()
32 | 
33 | 	return ptr
34 | }
35 | 
36 | func Restore(ptr unsafe.Pointer) (v interface{}) {
37 | 	if ptr == nil {
38 | 		return nil
39 | 	}
40 | 
41 | 	mutex.RLock()
42 | 	v = store[ptr]
43 | 	mutex.RUnlock()
44 | 	return
45 | }
46 | 
47 | func Unref(ptr unsafe.Pointer) {
48 | 	if ptr == nil {
49 | 		return
50 | 	}
51 | 
52 | 	mutex.Lock()
53 | 	delete(store, ptr)
54 | 	mutex.Unlock()
55 | 
56 | 	C.free(ptr)
57 | }
58 | 


--------------------------------------------------------------------------------