JNA 调用操作系统函数和系统调用

2019-05-08 22:20 Loull 阅读(2799) 评论(0) 编辑收藏举报

linux系统调用syscall 表：https://filippo.io/linux-syscall-table/

Linux Namespace 特性简要介绍

原文：https://iliangqunru.bitcron.com/post/2018/jna-shi-ji-kai-fa-zhong-ruo-gan-wen-ti-jie-jue-fang-fa

其他：

JNI的替代者—使用JNA访问Java外部功能接口

Invoke Syscalls from Java

java发起系统调用，本质还是用了JNA，调用OS提供的syacall函数：

import com.sun.jna.Library;
import com.sun.jna.Native;

public class Test {
    public interface CStdLib extends Library {
        int syscall(int number, Object... args);
    }

    public static void main(String[] args) {
        CStdLib c = (CStdLib)Native.loadLibrary("c", CStdLib.class);

        // WARNING: These syscall numbers are for x86 only
        System.out.println("PID: " + c.syscall(20));
        System.out.println("UID: " + c.syscall(24));
        System.out.println("GID: " + c.syscall(47));
        c.syscall(39, "/tmp/create-new-directory-here");
    }
}

很早就已经听说过 JNI（Java Native Interface）Java 本地接口，奈何调用本地动态链接库太过于复杂，就一直没有再尝试。而最近因为工作需要调用 Windows DLL 动态链接库（对应 Linux 中 so 文件），而对 JNA 有了入坑体验，对实际工作中遇到的问题做出总结。

1. 调用 Windows 窗口打印Hello World

pom 依赖

<dependency>
            <groupId>net.java.dev.jna</groupId>
            <artifactId>jna</artifactId>
            <version>latest</version>
        </dependency>

JNA 在加载驱动时提供两种加载方式， 直接映射 和 接口生成。

接口生成

public interface HelixcsDll extends StdCallLibrary {
        // loadLibary 为动态链接库加载目录
        HelixcsDll HELIXCS_DLL = Native.loadLibrary("helixcs.dll", HelixcsDll.class);
        // 在 dll 中存在相同 SomeFunction 的函数 
        void SomeFunction(String content);
    }
    
    // 调用
    HelixcsDll.HELIXCS_DLL.SomeFunction("Hello World");

直接映射

class Helixcs{
        static {
            Native.register("helixcs.dll");
        }
        // 映射为本地方法
        public static  native void SomeFunction(String content);

        public static void main(String[] args) {
            SomeFunction("Hello World");
        }
    }

官方例子：

package com.sun.jna.examples;

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;

/** Simple example of JNA interface mapping and usage. */
public class HelloWorld {

    // This is the standard, stable way of mapping, which supports extensive
    // customization and mapping of Java to native types.

    public interface CLibrary extends Library {
        CLibrary INSTANCE = (CLibrary)
            Native.load((Platform.isWindows() ? "msvcrt" : "c"),
                                CLibrary.class);

        void printf(String format, Object... args);
    }

    public static void main(String[] args) {
        CLibrary.INSTANCE.printf("Hello, World\n");
        for (int i=0;i < args.length;i++) {
            CLibrary.INSTANCE.printf("Argument %d: %s\n", i, args[i]);
        }
    }
}

2. C 类型和 Java 类型映射。

JNA 官方提供的默认类型映射

Default Type Mappings 默认类型映射

Java primitive types (and their object equivalents) map directly to the native C type of the same size.

Java 原始类型以相同的大小映射 C 类型。

Native Type	Size	Java Type	Common Windows Types
char	8-bit integer	byte	BYTE, TCHAR
short	16-bit integer	short	WORD
wchar_t	16/32-bit character	char	TCHAR
int	32-bit integer	int	DWORD
int	boolean value	boolean	BOOL
long	32/64-bit integer	NativeLong	LONG
long long	64-bit integer	long	__int64
float	32-bit FP	float
double	64-bit FP	double
char*	C string	String	LPTCSTR
void*	pointer	Pointer	LPVOID, HANDLE, LPXXX

未签名类型作为签名类型来映射。 C 中枚举类型可替换为 “int”。

Unsigned types use the same mappings as signed types. C enums are usually interchangeable with "int".

3. 官方提供的详细的类型映射

Marshalling/Unmarshalling (Java/Native Type Conversions)

C Type	Native Representation	Java Type
char	8-bit integer	byte
wchar_t	platform-dependent	char
short	16-bit integer	short
int	32-bit integer	int
int	boolean flag	boolean
enum	enumeration type	int (usually)
long long, __int64	64-bit integer	long
float	32-bit floating point	float
double	64-bit floating point	double
pointer (e.g. void*)	platform-dependent (32- or 64-bit pointer to memory)	`BufferPointer`
pointer (e.g. void*),array	32- or 64-bit pointer to memory (argument/return)contiguous memory (struct member)	<P>
In addition to the above types, which are supported at the native layer, the JNA Java library automatically handles the following types. All but `NativeMapped` and `NativeLong` are converted to `Pointer` before being passed to the native layer.
long	platform-dependent (32- or 64-bit integer)	`NativeLong`
const char*	NUL-terminated array (native encoding or `jna.encoding`)	`String`
const wchar_t*	NUL-terminated array (unicode)	`WString`
char	NULL-terminated array of C strings	`String[]`
wchar_t	NULL-terminated array of wide C strings	`WString[]`
void**	NULL-terminated array of pointers	`Pointer[]`
struct*struct	pointer to struct (argument or return) (`or explicitly`)struct by value (member of struct) (`or explicitly`)	`Structure`
union	same as `Structure`	`Union`
struct[]	array of structs, contiguous in memory	`Structure[]`
void (*FP)()	function pointer (Java or native)	`Callback`
pointer (<T> *)	same as `Pointer`	`PointerType`
other	integer type	`IntegerType`
other	custom mapping, depends on definition	`NativeMapped`

4. 经验总结默认映射关系

尽管 JNA 官方已经提供了详细的类型映射文档。但在实际中发现按照官方映射可能出现莫名问题。对此我们在实际开发中对于一些类型的映射报错，可以参考以下映射做出调整。

C类型	JNA类型	说明
char * out	Pointer	Pointer room = new Memory(30);
uchar * out	Pointer	Pointer room = new Memory(30);
long *	long [ ]
int *	init [ ]
int	int
char *	byte [ ]
char * argv[]	String []
uchar	int
long	NativeLong	兼容 32和64位

5. 常见错误

1. UnsatisfiedLinkError 问题

存在多个动态链接库之间调用情况，可能缺少其中某一个动态链接库文件。

2. Error Memory Access 问题

较大情况下存在参数类型映射错误，参考 JNA 类型映射。

3. dll can not find in win32/86

无法加载到动态链接库文件路径，需要将动态链接库放到项目根目录下，推荐开启 JNA 驱动加载 debug 模式，

System.setProperty("jna.debug_load", "true");

手动指定动态链接库文件路径

System.setProperty("jna.library.path",dllResourcePath);
System.setProperty("jna.platform.library.path",dllResourcePath);

4. 程序在运行一段时间后崩溃

在JNA crash-protection 中，官方文档说明的崩溃的主要原因,( These are often caused by improper mappings or invalid arguments passed to the native library.) 未知的参数类型映射导致vm崩溃。在很大程度上使用 Pointer 来作为 Java 通用映射类型。而 JNA 默认程序保护Native.setProtected(true)使得 java 错误来代替程序崩溃，可以设置 Native.setProtected(false) 来 dump 出崩溃日志。

问题可以反馈到 JNA Google Group : https://groups.google.com/forum/#!forum/jna-users

6. 参考

JNA Google Group : https://groups.google.com/forum/#!forum/jna-users
JNA API Documentation: https://java-native-access.github.io/jna/4.2.1/overview-summary.html
JNA VM Crashed Protection :http://java-native-access.github.io/jna/4.5.1/javadoc/overview-summary.html#crash-protection

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