Android的JNI - 呼叫AttachCurrentThread没有DetachCurrentThread [英] Android JNI - Call AttachCurrentThread without DetachCurrentThread

问题描述

我一直在阅读有关JNI的东西，似乎无法弄清楚发生了什么，如果一个线程开始 - >调用AttachCurrentThread（） - >使一些JNI调用 - >线程退出

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.

在理想情况下，我们应该线程退出之前调用DetachCurrentThread（），但是，会有什么影响，如果应用程序不这样做呢？它会导致内存泄漏或其他问题？

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;其他的后果是JVM特有的，大概为Android应用程序，其中JVM关闭时，在进程退出无关。有相当多的C ++包装来帮助管理线程的连接/断开，参见例如：的 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 法登 作为眼-opening的 链接 ;在Dalvik的，离开不调用线程 DetachCurrentThread（），使整个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.

下面是从官方模拟器logcat的基础上，的 HelloJni 从NDK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)

下面是相关的功能添加到<一个href=\"https://android.googlesource.com/platform/development/+/master/ndk/samples/hello-jni/jni/hello-jni.c\"相对=nofollow> 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 !");
}

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