如何从从 cgo 返回的 C 字符串中释放 java 中的内存（使用 jna）？

Question

戈朗

import "C"

//export MyFunction

func MyFunction(str *C.char) *C.char {

    goStr := C.GoString(str)

    msg := goStr + " world"

    return C.CString(msg)

}

func main() {}

爪哇岛

public interface MyLib extends Library {

    MyLib INSTANCE = Native.load("mylib.so", MyLib.class);

    String MyFunction(String str);

}

public class CGoExample {

    public static void main(String[] args) {

        String str = "Hello";

        String msg = MyLib.INSTANCE.MyFunction(str);

        System.out.println(msg);

    }

}

此代码有效，Java 字符串传递给 Go，Go 返回新字符串。我遇到的问题是，Go 返回的 CString 不会被 Java 或 Go 垃圾回收器解除分配。CGO文档指出“调用方有责任安排释放它，例如通过调用C.free”，当然，在我的情况下，调用C.free将不起作用，因为我返回CString，如果我在返回CString之前释放CString，我不会从Go函数中获得正确的响应。我也尝试过调用，但我发现在返回语句之前将调用延迟语句的困难方式。defer C.free(unsafe.Pointer(msg))

由于我需要返回CString，我假设它的内存需要从java中释放，我该怎么做？

编辑：

根据DanielWiddis的评论，我尝试了以下内容，但java进程存在于代码-1073741819。

// #include <stdlib.h>

import "C"

import "unsafe"

//export MyFunction

func MyFunction(str *C.char) *C.char {

    goStr := C.GoString(str)

    msg := goStr + " world"

    return C.CString(msg)

}

//export Free

func Free(str *C.char){

    C.free(unsafe.Pointer(str))

}

func main() {}

public interface MyLib extends Library {

    MyLib INSTANCE = Native.load("mylib.so", MyLib.class);

    String MyFunction(String str);

    void Free(String str);

}

public class CGoExample {

    public static void main(String[] args) {

        String str = "Hello";

        String msg = MyLib.INSTANCE.MyFunction(str);

        System.out.println(msg);

        MyLib.INSTANCE.Free(msg);

    }

}

Answer 1

的返回类型是指针：。C.CString()*C.char通过将其直接映射到 Java 端的 a，您将失去对该本机指针的跟踪，从而无法在以后跟踪和释放它。String最直接的解决方案是将其映射到Java端。在界面中：PointerPointer MyFunction(String str);void Free(Pointer str);然后使用它：Pointer pMsg = MyLib.INSTANCE.MyFunction(str);System.out.println(pMsg.getString(0));MyLib.INSTANCE.Free(pMsg);在这种情况下，（8 位）字符数组也可能有效。就个人而言，我可能会将类型安全指针与一些面向对象的帮助器方法一起使用，例如：byte[]class CStringPtr extends PointerType {&nbsp; &nbsp; public CStringPtr(String str) {&nbsp; &nbsp; &nbsp; &nbsp; super(MyLib.INSTANCE.MyFunction(str));&nbsp; &nbsp; }&nbsp; &nbsp; public String getString() {&nbsp; &nbsp; &nbsp; &nbsp; return this.getPointer().getString(0);&nbsp; &nbsp; }&nbsp; &nbsp; public void free() {&nbsp; &nbsp; &nbsp; &nbsp; MyLib.INSTANCE.Free(this.getPointer());&nbsp; &nbsp; }}这将使你的代码：CStringPtr pMsg = new CStringPtr(str);System.out.println(pMsg.getString());pMsg.free();

Answer 2

根据DanielWiddis的评论，我想出了以下解决方案，该解决方案可以成功为所有涉及的对象分配内存。package main// #include <stdlib.h>import "C"import (&nbsp; &nbsp; "unsafe")//export MyFunctionfunc MyFunction(cStr *C.char) *C.char {&nbsp; &nbsp; str := C.GoString(cStr)&nbsp; &nbsp; msg := str + " world"&nbsp; &nbsp; return C.CString(msg)}//export Freefunc Free(str *C.char){&nbsp; &nbsp; C.free(unsafe.Pointer(str))}func main() {}public interface MyLib extends Library {&nbsp; &nbsp; MyLib INSTANCE = Native.load("mylib.so", MyLib.class);&nbsp; &nbsp; Pointer MyFunction(Pointer ptr);&nbsp; &nbsp; void Free(Pointer ptr);}public class CGoExample {&nbsp; &nbsp; public static void main(String[] args) {&nbsp; &nbsp; &nbsp; &nbsp; // Create pointer with a String value&nbsp; &nbsp; &nbsp; &nbsp; String str = "Hello";&nbsp; &nbsp; &nbsp; &nbsp; Pointer ptr = new Memory(str.length() + 1);&nbsp; &nbsp; &nbsp; &nbsp; ptr.clear();&nbsp; &nbsp; &nbsp; &nbsp; ptr.setString(0, str);&nbsp; &nbsp; &nbsp; &nbsp; //Pass the pointer to Go function which returns the pointer of the message&nbsp; &nbsp; &nbsp; &nbsp; Pointer resultPtr = MyLib.INSTANCE.MyFunction(ptr);&nbsp; &nbsp; &nbsp; &nbsp; //Get the message String from the pointer&nbsp; &nbsp; &nbsp; &nbsp; String msg = resultPtr.getString(0);&nbsp; &nbsp; &nbsp; &nbsp; //Deallocate the memory for the message&nbsp; &nbsp; &nbsp; &nbsp; MyLib.INSTANCE.Free(resultPtr);&nbsp; &nbsp; &nbsp; &nbsp; System.out.println(msg);&nbsp; &nbsp; }}