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    public synchronized void start() {
        /**
         * This method is not invoked for the main method thread or "system"
         * group threads created/set up by the VM. Any new functionality added
         * to this method in the future may have to also be added to the VM.
         *
         * A zero status value corresponds to state "NEW".
         */
        // Android-changed: Replace unused threadStatus field with started field.
        // The threadStatus field is unused on Android.
        if (started)
            throw new IllegalThreadStateException();

        /* Notify the group that this thread is about to be started
         * so that it can be added to the group's list of threads
         * and the group's unstarted count can be decremented. */
        group.add(this);

        // Android-changed: Use field instead of local variable.
        // It is necessary to remember the state of this across calls to this method so that it
        // can throw an IllegalThreadStateException if this method is called on an already
        // started thread.
        started = false;
        try {
            // Android-changed: Use Android specific nativeCreate() method to create/start thread.
            // start0();
            nativeCreate(this, stackSize, daemon);
            started = true;
        } finally {
            try {
                if (!started) {
                    group.threadStartFailed(this);
                }
            } catch (Throwable ignore) {
                /* do nothing. If start0 threw a Throwable then
                  it will be passed up the call stack */
            }
        }
    }

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static void Thread_nativeCreate(JNIEnv* env, jclass, jobject java_thread, jlong stack_size,
                                jboolean daemon) {
  // There are sections in the zygote that forbid thread creation.
  Runtime* runtime = Runtime::Current();
  if (runtime->IsZygote() && runtime->IsZygoteNoThreadSection()) {
    jclass internal_error = env->FindClass("java/lang/InternalError");
    CHECK(internal_error != nullptr);
    env->ThrowNew(internal_error, "Cannot create threads in zygote");
    return;
  }

  Thread::CreateNativeThread(env, java_thread, stack_size, daemon == JNI_TRUE);
}

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void Thread::CreateNativeThread(JNIEnv* env, jobject java_peer, size_t stack_size, bool is_daemon) {
  CHECK(java_peer != nullptr);
  Thread* self = static_cast<JNIEnvExt*>(env)->GetSelf();

  ......

  int pthread_create_result = 0;
  if (child_jni_env_ext.get() != nullptr) {
    pthread_t new_pthread;
    pthread_attr_t attr;
    child_thread->tlsPtr_.tmp_jni_env = child_jni_env_ext.get();
    CHECK_PTHREAD_CALL(pthread_attr_init, (&attr), "new thread");
    CHECK_PTHREAD_CALL(pthread_attr_setdetachstate, (&attr, PTHREAD_CREATE_DETACHED),
                       "PTHREAD_CREATE_DETACHED");
    CHECK_PTHREAD_CALL(pthread_attr_setstacksize, (&attr, stack_size), stack_size);
    pthread_create_result = pthread_create(&new_pthread,
                                           &attr,
                                           gUseUserfaultfd ? Thread::CreateCallbackWithUffdGc
                                                           : Thread::CreateCallback,
                                           child_thread);
    CHECK_PTHREAD_CALL(pthread_attr_destroy, (&attr), "new thread");

    if (pthread_create_result == 0) {
      // pthread_create started the new thread. The child is now responsible for managing the
      // JNIEnvExt we created.
      // Note: we can't check for tmp_jni_env == nullptr, as that would require synchronization
      //       between the threads.
      child_jni_env_ext.release();  // NOLINT pthreads API.
      return;
    }
  }

  ......
}

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int pthread_create(pthread_t* thread_out, pthread_attr_t const* attr,
                   void* (*start_routine)(void*), void* arg) {
  ......
}

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status_t Thread::run(const char* name, int32_t priority, size_t stack)
{
    Mutex::Autolock _l(mLock);
    if (mRunning) {
      	// thread already started
        return INVALID_OPERATION;
    }
    ...
    mRunning = true;

    bool res;

    if (mCanCallJava) {
        // 创建能调用Java代码的Native线程
        res = createThreadEtc(_threadLoop,
                this, name, priority, stack, &mThread);
    } else {
        // 创建只能调用C/C++代码的Native线程
        res = androidCreateRawThreadEtc(_threadLoop,
                this, name, priority, stack, &mThread);
    }

    if (res == false) {
        return UNKNOWN_ERROR;
    }
    return NO_ERROR;
}

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int androidCreateRawThreadEtc(android_thread_func_t entryFunction,
                               void *userData,
                               const char* threadName __android_unused,
                               int32_t threadPriority,
                               size_t threadStackSize,
                               android_thread_id_t *threadId)
{
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

#if defined(__ANDROID__)  /* valgrind is rejecting RT-priority create reqs */
    if (threadPriority != PRIORITY_DEFAULT || threadName != NULL) {
        // Now that the pthread_t has a method to find the associated
        // android_thread_id_t (pid) from pthread_t, it would be possible to avoid
        // this trampoline in some cases as the parent could set the properties
        // for the child.  However, there would be a race condition because the
        // child becomes ready immediately, and it doesn't work for the name.
        // prctl(PR_SET_NAME) only works for self; prctl(PR_SET_THREAD_NAME) was
        // proposed but not yet accepted.
        thread_data_t* t = new thread_data_t;
        t->priority = threadPriority;
        t->threadName = threadName ? strdup(threadName) : NULL;
        t->entryFunction = entryFunction;
        t->userData = userData;
        entryFunction = (android_thread_func_t)&thread_data_t::trampoline;
        userData = t;
    }
#endif

    if (threadStackSize) {
        pthread_attr_setstacksize(&attr, threadStackSize);
    }

    errno = 0;
    pthread_t thread;
    int result = pthread_create(&thread, &attr,
                    (android_pthread_entry)entryFunction, userData);
    pthread_attr_destroy(&attr);
    if (result != 0) {
        ALOGE("androidCreateRawThreadEtc failed (entry=%p, res=%d, %s)\n"
             "(android threadPriority=%d)",
            entryFunction, result, strerror(errno), threadPriority);
        return 0;
    }

    // Note that *threadID is directly available to the parent only, as it is
    // assigned after the child starts.  Use memory barrier / lock if the child
    // or other threads also need access.
    if (threadId != nullptr) {
        *threadId = (android_thread_id_t)thread; // XXX: this is not portable
    }
    return 1;
}

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int Thread::_threadLoop(void* user)
{
    Thread* const self = static_cast<Thread*>(user);

    sp<Thread> strong(self->mHoldSelf);
    wp<Thread> weak(strong);
    self->mHoldSelf.clear();

#if defined(__ANDROID__)
    // this is very useful for debugging with gdb
    self->mTid = gettid();
#endif

    bool first = true;

    do {
        bool result;
        if (first) {
            first = false;
            self->mStatus = self->readyToRun();
            result = (self->mStatus == OK);

            if (result && !self->exitPending()) {
                // Binder threads (and maybe others) rely on threadLoop
                // running at least once after a successful ::readyToRun()
                // (unless, of course, the thread has already been asked to exit
                // at that point).
                // This is because threads are essentially used like this:
                //   (new ThreadSubclass())->run();
                // The caller therefore does not retain a strong reference to
                // the thread and the thread would simply disappear after the
                // successful ::readyToRun() call instead of entering the
                // threadLoop at least once.
                result = self->threadLoop();
            }
        } else {
            result = self->threadLoop();
        }

        // establish a scope for mLock
        {
        Mutex::Autolock _l(self->mLock);
        if (result == false || self->mExitPending) {
            self->mExitPending = true;
            self->mRunning = false;
            // clear thread ID so that requestExitAndWait() does not exit if
            // called by a new thread using the same thread ID as this one.
            self->mThread = thread_id_t(-1);
            // note that interested observers blocked in requestExitAndWait are
            // awoken by broadcast, but blocked on mLock until break exits scope
            self->mThreadExitedCondition.broadcast();
            break;
        }
        }

        // Release our strong reference, to let a chance to the thread
        // to die a peaceful death.
        strong.clear();
        // And immediately, re-acquire a strong reference for the next loop
        strong = weak.promote();
    } while(strong != nullptr);

    return 0;
}

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// Create thread with lots of parameters
inline bool createThreadEtc(thread_func_t entryFunction,
                            void *userData,
                            const char* threadName = "android:unnamed_thread",
                            int32_t threadPriority = PRIORITY_DEFAULT,
                            size_t threadStackSize = 0,
                            thread_id_t *threadId = nullptr)
{
    return androidCreateThreadEtc(entryFunction, userData, threadName,
        threadPriority, threadStackSize, threadId) ? true : false;
}

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static android_create_thread_fn gCreateThreadFn = androidCreateRawThreadEtc;

int androidCreateThreadEtc(android_thread_func_t entryFunction,
                            void *userData,
                            const char* threadName,
                            int32_t threadPriority,
                            size_t threadStackSize,
                            android_thread_id_t *threadId)
{
    return gCreateThreadFn(entryFunction, userData, threadName,
        threadPriority, threadStackSize, threadId);
}

void androidSetCreateThreadFunc(android_create_thread_fn func)
{
    gCreateThreadFn = func;
}

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/*
 * Register android native functions with the VM.
 */
/*static*/ int AndroidRuntime::startReg(JNIEnv* env)
{
    ATRACE_NAME("RegisterAndroidNatives");
    /*
     * This hook causes all future threads created in this process to be
     * attached to the JavaVM.  (This needs to go away in favor of JNI
     * Attach calls.)
     */
    androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);

    ALOGV("--- registering native functions ---\n");

    /*
     * Every "register" function calls one or more things that return
     * a local reference (e.g. FindClass).  Because we haven't really
     * started the VM yet, they're all getting stored in the base frame
     * and never released.  Use Push/Pop to manage the storage.
     */
    env->PushLocalFrame(200);

    if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
        env->PopLocalFrame(NULL);
        return -1;
    }
    env->PopLocalFrame(NULL);

    //createJavaThread("fubar", quickTest, (void*) "hello");

    return 0;
}

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/*
 * This is invoked from androidCreateThreadEtc() via the callback
 * set with androidSetCreateThreadFunc().
 *
 * We need to create the new thread in such a way that it gets hooked
 * into the VM before it really starts executing.
 */
/*static*/ int AndroidRuntime::javaCreateThreadEtc(
                                android_thread_func_t entryFunction,
                                void* userData,
                                const char* threadName,
                                int32_t threadPriority,
                                size_t threadStackSize,
                                android_thread_id_t* threadId)
{
    void** args = (void**) malloc(3 * sizeof(void*));   // javaThreadShell must free
    int result;

    LOG_ALWAYS_FATAL_IF(threadName == nullptr, "threadName not provided to javaCreateThreadEtc");

    args[0] = (void*) entryFunction;
    args[1] = userData;
    args[2] = (void*) strdup(threadName);   // javaThreadShell must free

    result = androidCreateRawThreadEtc(AndroidRuntime::javaThreadShell, args,
        threadName, threadPriority, threadStackSize, threadId);
    return result;
}

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int androidCreateRawThreadEtc(android_thread_func_t entryFunction,
                               void *userData,
                               const char* threadName __android_unused,
                               int32_t threadPriority,
                               size_t threadStackSize,
                               android_thread_id_t *threadId)
{
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

#if defined(__ANDROID__)  /* valgrind is rejecting RT-priority create reqs */
    if (threadPriority != PRIORITY_DEFAULT || threadName != NULL) {
        // Now that the pthread_t has a method to find the associated
        // android_thread_id_t (pid) from pthread_t, it would be possible to avoid
        // this trampoline in some cases as the parent could set the properties
        // for the child.  However, there would be a race condition because the
        // child becomes ready immediately, and it doesn't work for the name.
        // prctl(PR_SET_NAME) only works for self; prctl(PR_SET_THREAD_NAME) was
        // proposed but not yet accepted.
        thread_data_t* t = new thread_data_t;
        t->priority = threadPriority;
        t->threadName = threadName ? strdup(threadName) : NULL;
        t->entryFunction = entryFunction;
        t->userData = userData;
        entryFunction = (android_thread_func_t)&thread_data_t::trampoline;
        userData = t;
    }
#endif

    if (threadStackSize) {
        pthread_attr_setstacksize(&attr, threadStackSize);
    }

    errno = 0;
    pthread_t thread;
    int result = pthread_create(&thread, &attr,
                    (android_pthread_entry)entryFunction, userData);
    pthread_attr_destroy(&attr);
    if (result != 0) {
        ALOGE("androidCreateRawThreadEtc failed (entry=%p, res=%d, %s)\n"
             "(android threadPriority=%d)",
            entryFunction, result, strerror(errno), threadPriority);
        return 0;
    }

    // Note that *threadID is directly available to the parent only, as it is
    // assigned after the child starts.  Use memory barrier / lock if the child
    // or other threads also need access.
    if (threadId != nullptr) {
        *threadId = (android_thread_id_t)thread; // XXX: this is not portable
    }
    return 1;
}

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/*
 * When starting a native thread that will be visible from the VM, we
 * bounce through this to get the right attach/detach action.
 * Note that this function calls free(args)
 */
/*static*/ int AndroidRuntime::javaThreadShell(void* args) {
    void* start = ((void**)args)[0];
    void* userData = ((void **)args)[1];
    char* name = (char*) ((void **)args)[2];        // we own this storage
    free(args);
    JNIEnv* env;
    int result;

    /* hook us into the VM */
    if (javaAttachThread(name, &env) != JNI_OK)
        return -1;

    /* start the thread running */
    result = (*(android_thread_func_t)start)(userData);

    /* unhook us */
    javaDetachThread();
    free(name);

    return result;
}

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/*
 * Makes the current thread visible to the VM.
 *
 * The JNIEnv pointer returned is only valid for the current thread, and
 * thus must be tucked into thread-local storage.
 */
static int javaAttachThread(const char* threadName, JNIEnv** pEnv)
{
    JavaVMAttachArgs args;
    JavaVM* vm;
    jint result;

    vm = AndroidRuntime::getJavaVM();
    assert(vm != NULL);

    args.version = JNI_VERSION_1_4;
    args.name = (char*) threadName;
    args.group = NULL;

    result = vm->AttachCurrentThread(pEnv, (void*) &args);
    if (result != JNI_OK)
        ALOGI("NOTE: attach of thread '%s' failed\n", threadName);

    return result;
}

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// Check whether the current thread is attached. This is usually required
// to be the first check, as ScopedCheck needs a ScopedObjectAccess for
// checking heap values (and that will fail with unattached threads).
bool CheckAttachedThread(const char* function_name) {
  Thread* self = Thread::Current();
  if (UNLIKELY(self == nullptr)) {
    // Need to attach this thread for a proper abort to work. We prefer this
    // to get reasonable stacks and environment, rather than relying on
    // tombstoned.
    JNIEnv* env;
    Runtime::Current()->GetJavaVM()->AttachCurrentThread(&env, /* thr_args= */ nullptr);

    std::string tmp = android::base::StringPrintf(
        "a thread (tid %" PRId64 " is making JNI calls without being attached",
        static_cast<int64_t>(GetTid()));
    Runtime::Current()->GetJavaVM()->JniAbort(function_name, tmp.c_str());

    CHECK_NE(Runtime::Current()->GetJavaVM()->DetachCurrentThread(), JNI_ERR);
    return false;
  }
  return true;
}

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bool Runtime::AttachCurrentThread(const char* thread_name, bool as_daemon, jobject thread_group,
                                  bool create_peer, bool should_run_callbacks) {
  ScopedTrace trace(__FUNCTION__);
  Thread* self = Thread::Attach(thread_name,
                                as_daemon,
                                thread_group,
                                create_peer,
                                should_run_callbacks);
  // Run ThreadGroup.add to notify the group that this thread is now started.
  if (self != nullptr && create_peer && !IsAotCompiler()) {
    ScopedObjectAccess soa(self);
    self->NotifyThreadGroup(soa, thread_group);
  }
  return self != nullptr;
}