我一直在阅读关于JNI的东西,似乎无法弄清楚如果线程启动会发生什么 – >调用AttachCurrentThread() – >做一些JNI电话 – >螺纹出口.
理想情况下,我们应该在线程退出之前调用DetachCurrentThread(),但是如果应用程序不这样做,会有什么影响？会造成内存泄漏还是其他问题？
解决方法
不调用DetachCurrentThread()一定会造成内存泄漏;其他后果是JVM特定的,可能与
Android应用程序无关,JVM在进程退出时关闭.有很多C包装器有助于管理线程Attach / Detach,参见例如：
http://w01fe.com/blog/2009/05/c-callbacks-into-java-via-jni-made-easyier
更新：1000感谢fadden打开link;在Dalvik上,一个没有调用DetachCurrentThread()的线程会导致整个虚拟机和进程崩溃.
这是来自官方模拟器的logcat,我的代码基于来自NDK的HelloJni示例：
10-26 04:16:25.853: D/dalvikvm(1554): Trying to load lib /data/app-lib/com.example.hellojni-2/libhello-jni.so 0xb3d264f0 10-26 04:16:25.893: D/dalvikvm(1554): Added shared lib /data/app-lib/com.example.hellojni-2/libhello-jni.so 0xb3d264f0 10-26 04:16:25.893: D/dalvikvm(1554): No JNI_OnLoad found in /data/app-lib/com.example.hellojni-2/libhello-jni.so 0xb3d264f0,skipping init 10-26 04:16:26.463: D/gralloc_goldfish(1554): Emulator without GPU emulation detected. 10-26 04:16:31.033: D/threadFunction(1554): Attaching 10-26 04:16:31.173: D/threadFunction(1554): Not Detaching 10-26 04:16:31.183: D/dalvikvm(1554): threadid=11: thread exiting,not yet detached (count=0) 10-26 04:16:31.193: D/dalvikvm(1554): threadid=11: thread exiting,not yet detached (count=1) 10-26 04:16:31.193: E/dalvikvm(1554): threadid=11: native thread exited without detaching 10-26 04:16:31.193: E/dalvikvm(1554): VM aborting 10-26 04:16:31.213: A/libc(1554): Fatal signal 6 (SIGABRT) at 0x00000612 (code=-6),thread 1567 (xample.hellojni)
这是hello-jni.c添加的相关功能：
static JavaVM* jvm = 0;
static jobject activity = 0; // GlobalRef
void* threadFunction(void* irrelevant)
{
JNIEnv* env;
usleep(5000000);
__android_log_print(ANDROID_LOG_DEBUG,"threadFunction","Attaching");
(*jvm)->AttachCurrentThread(jvm,&env,NULL);
jclass clazz = (*env)->GetObjectClass(env,activity);
jmethodID methodID = (*env)->GetMethodID(env,clazz,"finish","()V" );
(*env)->CallVoidMethod(env,activity,methodID);
__android_log_print(ANDROID_LOG_DEBUG,"Not Detaching");
// (*jvm)->DetachCurrentThread(jvm);
}
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,jobject thiz )
{
(*env)->GetJavaVM(env,&jvm);
activity = (*env)->NewGlobalRef(env,thiz);
pthread_t hThread;
pthread_create(&hThread,NULL,&threadFunction,NULL);
return (*env)->NewStringUTF(env,"Hello from JNI !");
}
