ijkplayer message_loop

message_loop

在native_setup过程中

// ijkplayer_jni.c
static void
IjkMediaPlayer_native_setup(JNIEnv *env, jobject thiz, jobject weak_this)
{
    MPTRACE("%s\n", __func__);
    IjkMediaPlayer *mp = ijkmp_android_create(message_loop);
    ......
}

// ijkplayer_android.c
IjkMediaPlayer *ijkmp_android_create(int(*msg_loop)(void*))
{
    IjkMediaPlayer *mp = ijkmp_create(msg_loop);
    ......
}

// ijkplayer.c
IjkMediaPlayer *ijkmp_create(int (*msg_loop)(void*))
{
    ......
    mp->msg_loop = msg_loop;
	......
}

所以，msg_loop对应的是

// ijkplayer_jni.c
static int message_loop(void *arg)
{
    ......
    IjkMediaPlayer *mp = (IjkMediaPlayer*) arg;
    JNI_CHECK_GOTO(mp, env, NULL, "mpjni: native_message_loop: null mp", LABEL_RETURN);

    message_loop_n(env, mp);
	......
}

static void message_loop_n(JNIEnv *env, IjkMediaPlayer *mp)
{
    jobject weak_thiz = (jobject) ijkmp_get_weak_thiz(mp);
    JNI_CHECK_GOTO(weak_thiz, env, NULL, "mpjni: message_loop_n: null weak_thiz", LABEL_RETURN);

    while (1) {
        AVMessage msg;

        int retval = ijkmp_get_msg(mp, &msg, 1);
        if (retval < 0)
            break;

        // block-get should never return 0
        assert(retval > 0);

        switch (msg.what) {
        ......
        }
        msg_free_res(&msg);
    }

LABEL_RETURN:
    ;
}

// ijkplayer.c
int ijkmp_get_msg(IjkMediaPlayer *mp, AVMessage *msg, int block)
{
    assert(mp);
    while (1) {
        int continue_wait_next_msg = 0;
        int retval = msg_queue_get(&mp->ffplayer->msg_queue, msg, block);
        if (retval <= 0)
            return retval;

        switch (msg->what) {
        ......
        }
        if (continue_wait_next_msg) {
            msg_free_res(msg);
            continue;
        }

        return retval;
    }

    return -1;
}

// ff_ffmsg_queue.h
inline static int msg_queue_get(MessageQueue *q, AVMessage *msg, int block)
{
    AVMessage *msg1;
    int ret;

    SDL_LockMutex(q->mutex);

    for (;;) {
        if (q->abort_request) {
            ret = -1;
            break;
        }

        msg1 = q->first_msg;
        if (msg1) {
            q->first_msg = msg1->next;
            if (!q->first_msg)
                q->last_msg = NULL;
            q->nb_messages--;
            *msg = *msg1;
            msg1->obj = NULL;
#ifdef FFP_MERGE
            av_free(msg1);
#else
            msg1->next = q->recycle_msg;
            q->recycle_msg = msg1;
#endif
            ret = 1;
            break;
        } else if (!block) {
            ret = 0;
            break;
        } else {
            SDL_CondWait(q->cond, q->mutex);
        }
    }
    SDL_UnlockMutex(q->mutex);
    return ret;
}

可以看到，正常情况下，如果MessageQueue的first_msg字段为空，那么线程就会阻塞