Android JNI - Call AttachCurrentThread without DetachCurrentThread
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Android JNI - Call AttachCurrentThread without DetachCurrentThread
提问by pree
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.
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.
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?
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?
回答by Alex Cohn
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
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
Update:1000 thanks to faddenfor the eye-opening link; on Dalvik, a thread that exits without calling DetachCurrentThread(), brings the whole VM and the process crashing down.
Update:1000 thanks to faddenfor the eye-opening link; on Dalvik, a thread that exits without calling DetachCurrentThread(), brings the whole VM and the process crashing down.
Here is the logcat from the official emulator, my code based on the HelloJnisample from NDK:
Here is the logcat from the official emulator, my code based on the HelloJnisample 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)
Here is the relevant function added to 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 !");
}
A nice implementation of this strategy can be found in WebRTC git repo.
A nice implementation of this strategy can be found in WebRTC git repo.
