I want to call Java API from NDK C++ thread, but env->FindClass() return 0. But when I call Java API in main thread, it works well. I've already call AttachCurrentThread() in the thread, can anyone help me?
Here is the source code:
JAVA CODE:
public class simple_test extends Activity {
...
// This functin will be called in C++
public void PrintNdkLog(String slog) {
Log.e(logTagNDK, slog);
return;
}
}
C++ CODE:
static JavaVM* g_JavaVM = NULL;
jobject getInstance(JNIEnv *env, jclass obj_class)
{
jmethodID c_id = env->GetMethodID(obj_class, "<init>", "()V");
jobject obj = env->NewObject(obj_class, c_id);
return obj;
}
// JNI OnLoad
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved)
{
g_JavaVM = jvm;
return JNI_VERSION_1_6;
}
// Call JAVA API "PrintNdkLog" in this function
void PrintNdkLog(char *lpLog)
{
if (g_JavaVM == NULL)
return;
JNIEnv *env = NULL;
g_JavaVM->GetEnv((void**)&env, JNI_VERSION_1_6);
if (env == NULL)
return;
jclass cls = env->FindClass("com/myndk/simple_test");
if (cls != 0) // **cls will be 0 when PrintNdkLog() is called in thread**
{
LOGE("FindClass error %p", cls);
}
else
{
jmethodID mid;
jobject obj;
obj = getInstance(env, cls);
mid = env->GetMethodID(cls, "PrintNdkLog", "(Ljava/lang/String;)V");
if (mid != 0)
{
jstring jstrMSG = env->NewStringUTF(lpLog);
env->CallVoidMethod(obj, mid, jstrMSG);
}
}
}
// Call JAVA API in thread
static void* thread_test(void* ptr)
{
JNIEnv *envLocal;
int status = g_JavaVM->GetEnv((void **) &envLocal, JNI_VERSION_1_6);
if (status == JNI_EDETACHED)
{
status = g_JavaVM->AttachCurrentThread(&envLocal, NULL);
if (status != JNI_OK)
LOGE("AttachCurrentThread failed %d",status);
}
PrintNdkLog("bbb"); // This JAVA callback failed, and printed "FindClass error"
}
// Create thread
int NdkThread(AFX_THREADPROC pfnThreadProc, LPVOID pParam, int nPriority)
{
PrintNdkLog("aaa"); // This JAVA callback runs well
pthread_t pid;
pthread_create(&pid, NULL, thread_test, pParam);
}
I have solved it now. In NDK native thread, only can call static Java API. If you call env->FindClass(), it would trigger an exception. http://android.wooyd.org/JNIExample gived the detail info.
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