Determine how many mbytes are GC Android

[Tony Starkisi]

I have this code below which makes 300 http requests and each request returns 10000 rows from database. Total size of 10000 is approximately 0.4mb. So 300*0.4  = 120mb. I want to check the total Heap size whether it surpasses a certain  threshold lets say 256mb. If it does, then the app terminates. But sometimes depending the android version jvm doesnt call gc in time so it reaches 256mb but the 100mb might be garbage collectable and the app would terminate.

Is there a way to determine how many mbytes going to be freed?
Thank you
   

    ExecutorService service  = Executors.newFixedThreadPool(4);
    RequestQueue queue;
    AtomicInteger counter = new AtomicInteger(0);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        File cacheDir = new File(this.getCacheDir(), "Volley");
        queue = new RequestQueue(new DiskBasedCache(cacheDir), new BasicNetwork(new HurlStack()), 4);
        queue.start();
        start();
    }



    public void start(){

        String url ="...";
        for(int i =0 ; i<300; i++) {
            counter.incrementAndGet();
            StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                    new Response.Listener<String>() {
                        @Override
                        public void onResponse(String response) {

                            method(response);
                        }
                    }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Log.d("VolleyError", error.toString());
                }
            });
            stringRequest.setTag("a");
            queue.add(stringRequest);
        }
    }

    public synchronized void decreased(){

        if(counter.decrementAndGet()==0)
            start();
    }

    public void method( String response){

            Runnable task = new Runnable() {
                @Override
                public void run() {

                    List<Customer> customers= new ArrayList<>();
                    ObjectMapper objectMapper = new ObjectMapper();
                    TypeFactory typeFactory = objectMapper.getTypeFactory();
                    try {
                    customers= objectMapper.readValue(response, new TypeReference<List<Customer>>() {});

                                  //Simulate database insertion delay
                                  try {
                                        Thread.sleep(1000);
                                    } catch (InterruptedException e) {
                                       e.printStackTrace();
                                    }

                        decreased();
                    } catch (IOException e1) {
                        e1.printStackTrace();
                    }
                }
            };


        logHeap("");
        service.execute(task);

    }

[Pete Letkeman]

In Java there is not way to force garbage collection and there is also no way to determine how much memory would be freed if garbage collection occurs.
You can ask Java to run garbage collection by running System.gc() but that request may be ignored.
Given that you cannot enforce garbage collection using Java, you cannot know how much memory will be freed up when garbage collection happens.

But we are talking about Android and an alternative to using Java for Android programming is to use C or C++.
I do not know C or C++ enough to know how this is implemented in general or how it's implemented in Android.