OnBackpressureExample.java

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 * Copyright (c) 2015 Christos Froussios
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package itrx.chapter4.backpressure;

import static org.hamcrest.CoreMatchers.instanceOf;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotEquals;
import static org.junit.Assert.assertThat;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.TimeUnit;

import org.junit.Test;

import rx.Observable;
import rx.schedulers.Schedulers;
import rx.schedulers.TestScheduler;

public class OnBackpressureExample {
		
	public void exampleOnBackpressureBuffer() {
		Observable.interval(1, TimeUnit.MILLISECONDS)
		    .onBackpressureBuffer(1000)
		    .observeOn(Schedulers.newThread())
		    .subscribe(
		        i -> {
		            System.out.println(i);
		            try {
		                Thread.sleep(100);
		            } catch (Exception e) { }
		        },
		        System.out::println
		    );
		
		// 0
		// 1
		// 2
		// 3
		// 4
		// 5
		// 6
		// 7
		// 8
		// 9
		// 10
		// 11
		// rx.exceptions.MissingBackpressureException: Overflowed buffer of 1000
	}
	
	public void exampleOnBackpressureDrop() {
		Observable.interval(1, TimeUnit.MILLISECONDS)
	    .onBackpressureDrop()
	    .observeOn(Schedulers.newThread())
	    .subscribe(
	        i -> {
	            System.out.println(i);
	            try {
	                Thread.sleep(100);
	            } catch (Exception e) { }
	        },
	        System.out::println);
		
		// 0
		// 1
		// 2
		// ...
		// 126
		// 127
		// 12861
		// 12862
		// ...
	}
	
	
	//
	// Test
	//
	
	@Test
	public void testOnBackpressureBuffer() {
		TestScheduler scheduler = Schedulers.test();
		List<Long> received = new ArrayList<>();
		List<Throwable> errors = new ArrayList<>();
		ControlledPullSubscriber<Long> tester = new ControlledPullSubscriber<Long>(
			received::add,
			errors::add);
		
		// Subscriber accepts items once every 100ms
		scheduler.createWorker().schedulePeriodically(
			() -> tester.requestMore(1),
			0, 100, TimeUnit.MILLISECONDS);
		
		Observable.interval(1, TimeUnit.MILLISECONDS, scheduler)
		    .onBackpressureBuffer(1000)
		    .observeOn(scheduler)
		    .subscribe(tester);
		
		scheduler.advanceTimeBy(2000, TimeUnit.MILLISECONDS);
		assertEquals(Arrays.asList(0L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 11L), received);
		assertThat(
				errors.get(0),
				instanceOf(rx.exceptions.MissingBackpressureException.class));
	}
	
	@Test
	public void testOnBackpressureDrop() {
		TestScheduler scheduler = Schedulers.test();
		List<Long> received = new ArrayList<>();
		List<Throwable> errors = new ArrayList<>();
		ControlledPullSubscriber<Long> tester = new ControlledPullSubscriber<Long>(
				received::add,
				errors::add);
		
		// Subscriber accepts items once every 100ms
		scheduler.createWorker().schedulePeriodically(
			() -> tester.requestMore(1),
			0, 100, TimeUnit.MILLISECONDS);
		
		Observable.interval(1, TimeUnit.MILLISECONDS, scheduler)
		    .onBackpressureDrop()
		    .observeOn(scheduler)
		    .subscribe(tester);
		
		scheduler.advanceTimeBy(13000, TimeUnit.MILLISECONDS);
		assertEquals(129L, received.get(129).longValue());
		assertNotEquals(130L, received.get(130).longValue());
		
		
	}

}