Android JNI - 调用 AttachCurrentThread 而不使用 DetachCurrentThread

我一直在阅读有关 JNI 的内容，似乎无法弄清楚如果线程启动 -> 调用 AttachCurrentThread() -> 进行一些 JNI 调用 -> 线程退出会发生什么。

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？会导致内存泄漏或任何其他问题吗？

Not calling DetachCurrentThread() will definitely cause a memory leak; other consequences are JVM-specific, and probably irrelevant for Android apps, where the JVM shuts down when the process exits. There are quite a few C++ wrappers that help to manage thread Attach/Detach, see for example: http://w01fe.com/blog/2009/05/c-callbacks-into-java-via-jni-made-easyier http://w01fe.com/blog/2009/05/c-callbacks-into-java-via-jni-made-easyier

Update:1000 感谢fadden https://stackoverflow.com/users/294248/fadden为了大开眼界link https://android.googlesource.com/platform/dalvik/+/kitkat-release/vm/Thread.cpp;在 Dalvik 上，一个不调用就退出的线程DetachCurrentThread()，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HelloJni https://android.googlesource.com/platform/development/+/master/ndk/samples/hello-jni来自 NDK 的示例：

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)

这是添加的相关功能hello-jni.c https://android.googlesource.com/platform/development/+/master/ndk/samples/hello-jni/jni/hello-jni.c:

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, "threadFunction", "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 !");
}

WebRTC 中可以找到该策略的一个很好的实现git repo https://webrtc.googlesource.com/src/+/master/sdk/android/src/jni/jvm.cc#106.