Android JNI - 在没有 DetachCurrentThread 的情况下调用 AttachCurrentThread [英] Android JNI - Call AttachCurrentThread without DetachCurrentThread

问题描述

我一直在阅读有关 JNI 的内容，但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.

I have been reading about JNI stuff and can't seem to figure out what happens if a thread starts -> calls AttachCurrentThread() -> make some JNI calls -> thread exit.

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?它会导致内存泄漏或任何其他问题吗?

Ideally, we should call DetachCurrentThread() before thread exits, however, what are the implications if the app doesn't do that? Would it cause memory leak or any other problem?

推荐答案

不调用DetachCurrentThread()肯定会导致内存泄漏；其他后果是 JVM 特定的，可能与 Android 应用程序无关，其中 JVM 在进程退出时关闭.有很多 C++ 包装器可以帮助管理线程 Attach/Detach，例如:http://w01fe.com/blog/2009/05/c-callbacks-into-java-via-jni-made-easyier

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

更新: 1000 感谢 fadden 的关注-打开 链接;在 Dalvik 上，一个未调用 DetachCurrentThread() 的线程退出，导致整个 VM 和进程崩溃.

Update: 1000 thanks to fadden for the eye-opening link; on Dalvik, a thread that exits without calling DetachCurrentThread(), brings the whole VM and the process crashing down.

这是来自官方模拟器的 logcat，我的代码基于 HelloJni 来自 NDK 的示例:

Here is the logcat from the official emulator, my code based on the HelloJni sample from NDK:

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)

这里是添加到 hello-jni.c:

Here is the relevant function added to 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 !");
}

这个策略的一个很好的实现可以在 WebRTC git repo.

A nice implementation of this strategy can be found in WebRTC git repo.

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