How to create GstBuffer Pool in custom plugin - gstreamer

Question

I having a GST pipeline as shown below.
SRC ->A ->ROI ->B-> SINK
The custom elements (A, ROI and B) I has created by using the Gstreamer bad plugin tool element-maker as shown below.
./element-maker videofilter
I have removed the transform_frame() function from the above custom plugin source code and using transform_frame_ip() in order to use these plugin as a pass-through.
The above pipeline is working fine as a pass-through.
Requirement
Here, the 'ROI' element will produce multiple frames that will be passed to the element 'B' for further processing.
To implement this algorithm I have seen GstBuffer Pool concept in Gstreamer from the link mentioned below.
https://gstreamer.freedesktop.org/documentation/gstreamer/gstbufferpool.html?gi-language=c
My ROI function is acting like an Upstream element and below is the pool configuration inside the init_ROI element.
static void gst_ROI_init (GstROI *ROI){
/* GstBuffer Pool Config.*/
pool = gst_buffer_pool_new();
config = gst_buffer_pool_get_config(pool);
size = 420*420*3; // For RGB fromat.
min_ = 1;
max_ = 10;
caps = gst_caps_from_string("video/x-raw");
gst_buffer_pool_config_set_params (config, caps,
size, min_, max_);
gst_caps_unref(caps);
if ( gst_buffer_pool_set_config (pool, config)){
std::cout << "[INFO] Pool configuration done
successfully\n";
if( gst_buffer_pool_set_active( pool, TRUE )){
std::cout << "Successfully activated the pool
buffer\n";
}
else{
std::cout << "[ERROR] Failed to activate the
buffer pool\n";
}
} //end if
else {
std::cout << "[ERROR] Failed to set the pool
config.\n";
}
}
My **'B' element ** is working as a downstream element and below is the code to acquire the frames from pool.
gst_B_transform_frame_ip (GstVideoFilter * filter,
GstVideoFrame * frame)
{
/* GstBufferPool */
/*if (gst_buffer_pool_acquire_buffer(pool, &buf,
NULL) == GST_FLOW_EOS){ // pool variable is shared
variable ascross the ROI and B element.
std::cout << "[ERROR] Failed to acquire the frame\n";
}
Problem:
But the above implementation is not working as expected. It seems something I did wrong.
I have some doubts about the GstBuffer pool.
1- How to add the frames inside the buffer pool in the upstream element?
2- Is there any alternative and simple way to do the same. like I can create a sharable array of GstBuffer to store the n-cropped images and the same array I will access inside the B element instead of implementing the GstBuffer pool?
very new to this environment. any feedback will be useful for me.
thank you in advance.
Can any give their feedback on the above implementation and I will be great If anyone can share the reference code to implement the same GstBufferPool.