I'm a beginner on Android NDK, and less aware of C++. I have written some logic using C++ and then build them to .so file, then use it with JNI for my Android project, but sometimes it will raise crash in .so files.
I want to quickly fix this problem, I want to know if I can use try-catch syntax to my C++ code? (I tried, but it always reports compile error.) If yes, how can I do it?
C++ codes：
JNIEXPORT void JNICALL Java_xxoo_com_xxoo_model_ARDrawModel_draw(JNIEnv * env, jobject obj) {
try {
if(controller)
{
controller->Update(/*float dt*/);
controller->DrawGLScene();
}
} catch (int a) {
LOGD("drawModel---exception");
}
}
Compile error：
error: exception handling disabled, use -fexceptions to enable
Yes. you can use try catch in c++ NDK code, but it will not catch all native crashes.
And as your error says, you need to explicitly enable exceptions feature while compiling NDK code. To do so add
APP_CPPFLAGS += -fexceptions
to Application.mk file.
If you want to catch all possible NDK crashes check out https://github.com/xroche/coffeecatch library.
Related
When I perform a throw command in my native library, my Android application crashes. Does Android not support these calls? It never reaches the catch.
try
{
__android_log_print(ANDROID_LOG_ERROR, "nativeLib", "throw");
throw;
}
catch (...) {
__android_log_print(ANDROID_LOG_ERROR, "nativeLib", "catch");
}
I recently switched from gnustl_shared to c++_shared, I'm not sure if this has anything to do with my problem.
Developer guides say that gnustl_shared has exceptions enabled by default, but c++_shared does not. I have included the -fexceptions flag as describe in the guide.
https://developer.android.com/ndk/guides/cpp-support.html
This is expected behavior. From the C++ standard:
If no exception is presently being handled, executing a throw-expression with no operand calls terminate()(15.5.1).
If you want it to catch you need to throw something:
try
{
__android_log_print(ANDROID_LOG_ERROR, "nativeLib", "throw");
throw new std::exception();
}
catch (...) {
__android_log_print(ANDROID_LOG_ERROR, "nativeLib", "catch");
env->ExceptionCheck();
}
It looks like this is a known issue:
https://developer.android.com/ndk/guides/cpp-support.html
Compatibility
The NDK's libc++ is not stable. Not all the tests pass, and the test suite is not comprehensive. Some known issues are:
•Using c++_shared on ARM can crash when an exception is thrown.
•Support for wchar_t and the locale APIs is limited.
Has this severe error been established as a official bug within the Android developer community? If not, it should. It is really a major, major flaw in the design. Catastrophic.
The title says it all. I'm using NDK to build a native library for use with Unity (the game engine, not the Ubuntu shell). I already have much of the code in place and it works on my Xperia Z Ultra which runs Android 4.4.4. However, recently I sent the app to some other people to test on their phones, and it worked on none of their phones. They were using Android 4.0 and 4.1, so I tried running the app on my own Android 4.0.4 device (an old Xperia Mini Pro) and had the same problem. After much narrowing down, I've found out that the root of the problem is including OpenCV in the build, even if it's not referenced at all.
Here's the code I have now. First, the simplest CPP file you've seen:
//Test.cpp:
extern "C"
{
int Test(int a, int b)
{
return a + b;
}
}
Note how it doesn't even include anything from OpenCV. The makefile (or whatever it's called in the context of NDK, I'm mostly a Windows/Visual Studio person) is:
#Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
#---------------------------
#note: if I comment these lines out, the library works just fine.
#if I don't, it won't load at all.
#---------------------------
OPENCV_PACKAGE_DIR := D:\Eclipse\OpenCVAndroid\OpenCV-2.4.9-android-sdk
include $(OPENCV_PACKAGE_DIR)/sdk/native/jni/OpenCV.mk
LOCAL_MODULE := Test
LOCAL_SRC_FILES := Test.cpp
include $(BUILD_SHARED_LIBRARY)
Building this project gives me a "libTest.so" file. I put this into my Unity project, at Assets/Plugins/Android/ (I've also tried putting it in Plugins/Android/libs/armeabi-v7a/, no luck). I also have a script inside unity which invokes the library:
//TestNative.cs:
using UnityEngine;
using System.Collections;
using System.Runtime.InteropServices;
public class TestNative : MonoBehaviour
{
[DllImport("Test")]
public static extern int Test(int a, int b);
void OnGUI()
{
try
{
GUI.Label(new Rect(0, 0, 100, 100), "2 + 3 = " + Test(2, 3));
}
catch (System.Exception e)
{
GUI.Label(new Rect(0, 0, 600, 400), e.GetType().ToString() + " " + e.Message + "\n" + e.StackTrace);
}
}
}
When I run this on my Z Ultra, it works just fine. When I run it on the Mini Pro, it fails with the exception "DllNotFoundException: Test". I've checked logcat for errors, and this is what it says:
01-06 06:46:27.660: D/dalvikvm(11135): Trying to load lib /mnt/asec/com.cet.sna2-2/lib/libTest.so 0x2bb86638
01-06 06:46:27.660: D/dalvikvm(11135): Trying to load lib /mnt/asec/com.cet.sna2-2/lib/libTest.so 0x2bb86638
01-06 06:46:27.660: E/Unity(11135): Unable to find Test
It doesn't say anything else, it just fails. The fact that it works on 4.4.4 makes me think it might have something to do with build configurations or something like that, but I can't figure out what it is. Any ideas? Thanks.
I found out, after much trial and error, that the reason for the error is that Android somehow manages to mess the library dependencies up. The work-around is to manually load the libraries in the specific order of their dependencies, using LoadLibrary. This can be done in Unity using AndroidJavaClass to avoid having to write an entire jar library just for loading the native ones.
You have to build a .so that correspond to the architecture of the device your are using.
You should look at this link :
https://developer.nvidia.com/AndroidWorks
It provides useful tools to develop on Android with Visual Studio
You can easily configure an Android Dynamic Library (.so) that correspond to the architecture you need :)
Environment: Latest NDK + Eclipse Juno + ADT + CDT. Everything is up to date.
When I try to debug my Android application natively, I get the following error:
warning: Unable to find dynamic linker breakpoint function.
GDB will retry eventurally. Meanwhile, it is likely
that GDB is unable to debug shared library initializers
or resolve pending breakpoints after dlopen().
To ensure it is not my specific application, I created a simple dummy application. Here are the steps I took.
From Eclipse, create a new Android application project (with min-sdk 16 and target-sdk 21)
Added a class:
package com.test.mytest1;
public class MyNative {
static {
android.os.Debug.waitForDebugger();
System.loadLibrary("mytest1");
}
native public static void init();
}
Note that I have added a line to wait for the debugger to initialize.
Called MyNative.init() from MainActivity's onCreate() method.
From preferences, fixed NDK to point to C:\adt\ndk directory.
From the project menu, selected Android Tools-->Add Native Support.
From Properties->C++ Build, set build command to "ndk-build NDK_DEBUG=1"
Here is the code in mytest1.cpp:
static int x = 0;
JNIEXPORT void JNICALL Java_com_test_mytest1_MyNative_init(JNIEnv *, jclass)
{
x++;
}
Added Application.mk in jni directory:
APP_ABI := armeabi-v7a
APP_PLATFORM := android-16
Now, when I try to run the app as native application, it fails with the above mentioned message.
When I look at the apk file, lib/armeabi-v7a does contain gdbserver as well as libmytest1.so files.
The app does work. If I add a log() statement in my native method, it does get displayed in LogCat.
I am confused and tired. A simple thing like thing should just work. Wondering if you can share what you did differently to make it work. Regards.
android.os.Debug.waitForDebugger() is for JAVA debugging.
To debug Native code add sleep(seconds) before your first breakpoint , that's way gdb have to to connect gdbserver
JNIEXPORT void JNICALL Java_com_test_mytest1_MyNative_init(JNIEnv *, jclass)
{
sleep(10);
x++;
}
I'm looking for clues why my Android app sporadically throws an UnsatisfiedlinkError exception on a specific ndk call:
I have an Android app that loads one native library through ndk.
The native library is written in C++ and uses STL (in my makefile I have set APP_STL := stlport_static). No other libraries are used or required. The native library has about 300 native methods for about 20 java classes.
All works fine, most of the time. But every now and then my users get an UnsatisfiedLinkError exception. The exception is always triggered at the same spot with the same native function call, but strangely enough it is not even the first call to a native function, not even the first call to that specific native function.
Any clue would be welcome why one specific native call could fails. Can ndk easily be corrupted? How do you debug for such a problem?
Simple test programs with the same call work just fine. Nevertheless here's some parts of the source code:
Here's the problem ndk function in Java:
public class Server {
...
static private native long longObserveError( );
...
}
Here's the header file:
extern "C" {
...
JNIEXPORT jlong JNICALL Java_be_gentgo_tetsuki_Server_longObserveError
(JNIEnv *, jclass);
...
}
And here's the implementation:
IGSProtocol *server = 0; // initialized later...
JNIEXPORT jlong JNICALL Java_be_gentgo_tetsuki_Server_longObserveError
(JNIEnv *env, jclass)
{
Messenger &mess = server->ObserveError( );
return (long)(&mess);
}
What is the name of your library file? I came across another SO post (https://stackoverflow.com/a/18024816) where the guy had a library name that was conflicting with a system library that was only present on some devices. Renaming his library fixed the problem.
I'm trying to use the NDK with C++ and can't seem to get the method naming convention correct. my native method is as follows:
extern "C" {
JNIEXPORT void JNICALL Java_com_test_jnitest_SurfaceRenderer_drawFromJni
(JNIEnv* env, jclass c)
{
//
}
}
with a header wrapped in extern "C" {} aslo.
Everything compiles fine, creates a .so file and copies to the libs folder under my project, but when I debug and run in Eclipse I keep getting a log cat message that of "no implementation found for native...". Is there something i'm missing as all the NDK examples are in C?
Thanks.
There are a couple of things that can lead to "no implementation found". One is getting the function prototype name wrong, another is failing to load the .so at all. Are you sure that System.loadLibrary() is being called before the method is used?
If you don't have a JNI_OnLoad function defined, you may want to create one and have it spit out a log message just to verify that the lib is getting pulled in successfully.
You already dodged the most common problem -- forgetting to use extern "C" -- so it's either the above or some slight misspelling. What does the Java declaration look like?
An additional cause for this error: your undecorated native method name must not contain an underscore!
For example, I wanted to export a C function named AudioCapture_Ping(). Here is my export declaration in C:
JNI_EXPORT int Java_com_obsidian_mobilehashhost_MainActivity_AudioCapture_Ping(JNIEnv *pJniEnv, jobject object); //Notice the underscore before Ping
Here was my Java class importing the function:
package com.obsidian.mobileaudiohashhost;
...
public class MainActivity extends Activity {
private native int AudioCapture_Ping(); // FAILS
...
I could not get Android to dynamically link to my native method until I removed the underscore:
JNI_EXPORT int Java_com_obsidian_mobilehashhost_MainActivity_AudioCapturePing(JNIEnv *pJniEnv, jobject object);
package com.obsidian.mobileaudiohashhost;
...
public class MainActivity extends Activity {
private native int AudioCapturePing(); // THIS WORKS!
...
I had the same problem, but to me the error was in the file Android.mk. I had it:
LOCAL_SRC_FILES := A.cpp
LOCAL_SRC_FILES := B.cpp
but should have this:
LOCAL_SRC_FILES := A.cpp
LOCAL_SRC_FILES += B.cpp
note the detail += instead :=
I hope that helps.
Called extern "C" as provided in the automatically-generated Studio example, but forgot to wrap the entire rest of the file, including following functions, in {} brackets. Only the first function worked.
An additional reason: Use LOCAL_WHOLE_STATIC_LIBRARIES instead of LOCAL_STATIC_LIBRARIES in android.mk. This stops the library from optimizing out unused API calls because the NDK cannot detect the use of the native bindings from java code.
There is a cpp example under apps in ndk:
https://github.com/android/ndk-samples/blob/master/hello-gl2/app/src/main/cpp/gl_code.cpp
Use javah (part of Java SDK). Its the tool exactly for this (generates .h header from .class file).
If your package name includes _ character, you should write 1(one) after _ character as shown below:
MainActivity.java
package com.example.testcpp_2;
native-lib.cpp
JNICALL
Java_com_example_testcpp_12_MainActivity_stringFromJNI(
I try all above solutions, but no one can solved my build error(jni java.lang.UnsatisfiedLinkError: No implementation found for...),
at last I found that I forget to add my verify.cpp source file to CMakeList.txt add_library segement(verify.cpp is auto generate by Ctrl + Enter short key, maybe other file name), hope my response can help some one.
my build environment: Gradle + CMake
I Faced the same problem, and in my case the reason was that I had underscore in package name "RFID_Test"
I renamed the Package and it worked.
Thanks user1222021
I faced the same problem twice. It happened, that the phone I tried to start the app from Android Studio used an API level that I haven't downloaded yet in Android Studio.
Upgrade Android Studio to the latest version
Download the necessary API from within Android Studio