I have question is it possible to return from Go function pointer on C? For example main.c can be:
struct open_db_return db_ptr = open_db(db_path);
GoSlice backet = {"DB", 2, 2};
GoSlice key = {"CONFIG", 6, 6};
struct get_value_return val = get_value(db_ptr.r0, backet, key);
close_db(db_ptr.r0);
Go code is next:
//export open_db
func open_db(path string) (interface{}, error) {
db, err := db.Open(path, 0600, nil)
if err != nil {
return nil, err
}
return db, nil
}
//export close_db
func close_db(db interface{}) {
ldb := db.(*db.DB)
ldb.Close()
}
//export get_value
func get_value(db interface{}, backet_name []byte, key_name []byte) ([]byte, error) {
ldb := db.(*db.DB)
var value []byte
fn := func(tx *db.Tx) error {
value = tx.Bucket(backet_name).Get(key_name)
return nil
}
return value, ldb.View(fn)
}
After cgo command go build -buildmode=c-archive test.go i receive header file and trying to link it into my c project via command gcc -g -pthread main.c test.a -o main, all compiled and linked succsesful but in runtime i receive next error: panic: runtime error: cgo result has Go pointer The idea is receive pointer to DB in c, do some work and when DB not needed close DB.
As JimB says; this probably won't work (it's called unsafe for a reason). Even if you manage to cast the pointer to something that is consumable by C, there is major risk because of the garbage collection in Go potentially freeing the underlying resources because Go doesn't know about the usages in C
I think the signature for open_db should be: func open_db(path string) (unsafe.Pointer, error)
And the variable db should be converted to unsafe.Pointer; naively like this: return unsafe.Pointer(db), err but I don't know the specifics of the database implementation in this case.
Your close_db function will probably also need to accept an unsafe.Pointer instead of an interface{}