[英]Android NDK Native Function Call Issue
I am attempting to write an Android application that makes use of the GNU Scientific Library (GSL). 我正在尝试编写一个使用GNU科学库(GSL)的Android应用程序。 In particular, I am interested in 'libgslcblas.so' for its BLAS implementation.
我尤其对'libgslcblas.so'的BLAS实现感兴趣。 I decided to take advantage of the Android NDK and write a Java program that loads the library and makes the appropriate function calls.
我决定利用Android NDK并编写一个Java程序来加载该库并进行适当的函数调用。
To test how this would work, I attempted to write a simple program that would load 'libm.so' and make an arbitrary function call. 为了测试其工作方式,我尝试编写一个简单的程序来加载“ libm.so”并进行任意函数调用。 This seemed about a trivial a use-case of the NDK as I could think of, yet I ran into the following issue:
我可以想到,这似乎是一个简单的NDK用例,但遇到了以下问题:
07-05 18:11:07.264: I/System.out(1298): debugger has settled (1464)
07-05 18:11:07.583: D/dalvikvm(1298): No JNI_OnLoad found in /system/lib/libm.so 0x41345988, skipping init
07-05 18:11:07.903: W/dalvikvm(1298): No implementation found for native Lissm/libctest/LibCtest;.sqrt (D)D
My code is as follows: 我的代码如下:
package issm.libctest;
import android.os.Bundle;
import android.app.Activity;
import android.widget.TextView;
public class LibCtest extends Activity
{
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
setContentView(R.layout.activity_lib_ctest);
double x = sqrt(4);
tv.setText( "Sine of: " + x);
setContentView(tv);
}
public native double sqrt(double x);
static
{
System.load("/system/lib/libm.so");
}
}
I really do not understand the problem. 我真的不明白这个问题。 As I said, this is the simplest use of the NDK I can think of.
如我所说,这是我能想到的最简单的NDK使用方法。 Can someone help me resolve this issue?
有人可以帮我解决这个问题吗?
Thanks! 谢谢!
Read up on JNI. 阅读JNI。 In short, arbitrary global C functions are NOT callable from Java via NDK.
简而言之,不能通过NDK从Java调用任意全局C函数。 In order to be callable, a function needs a very specific signature, along the lines of:
为了可调用,一个函数需要一个非常特定的签名,大致如下:
void Java_com_mypackage_MyClass_MyMethod(JNIEnv *jni, jobject thiz, jint arg1);
On the Java side, that would be a method of class MyClass
in package com.mypackage
: 在Java方面,这将是
com.mypackage
包中MyClass
类的方法:
native void MyMethod(int arg1);
Obviosly, vanilla sqrt
won't fit the bill. 显然,香草
sqrt
不适合该法案。 So you need to provide a Java-friendly wrapper for every function you intend to call from Java. 因此,您需要为要从Java调用的每个函数提供一个Java友好的包装器。 With that in mind, you'll probably want to provide wrappers for higher-level concepts that mere math primitives.
考虑到这一点,您可能希望为仅数学基元的高级概念提供包装。 The Java/C border is messy;
Java / C边界杂乱无章; the less you cross it, the better.
越少越好。
Also, the library needs to be built from sources specifically for Android. 另外,该库需要从专门用于Android的源构建。 NDK has the tools for that.
NDK具有用于该目的的工具。 A ready-made binary for another platform (say, Linux or Windows) won't be usable.
用于其他平台(例如Linux或Windows)的现成二进制文件将无法使用。
EDIT: The javah
tool from JDK can take a Java class with a bunch of native
declarations and make skeleton H/C files with dummy implementations. 编辑:来自JDK的
javah
工具可以采用带有一堆native
声明的Java类,并使用伪实现来制作骨架H / C文件。 Essentially, translate the method prototypes from Java to C along the JNI rules. 本质上,按照JNI规则将方法原型从Java转换为C。
确保您要使用的库(及其依赖项)是针对目标平台(Android Native平台)构建的。
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