Benchmark StackView

gistfile1.txt

Code:

```Java
import de.embl.cba.bdp2.imglib2.LazyStackView;
import net.imglib2.RandomAccess;
import net.imglib2.RandomAccessibleInterval;
import net.imglib2.img.array.ArrayImgs;
import net.imglib2.type.numeric.integer.ByteType;
import net.imglib2.view.StackView;

import java.util.ArrayList;

public class BenchmarkLazyStackView
{
	public static void main( String[] args )
	{
		final int numSlices = 10000;
		final int nx = 100;
		final int ny = 100;
		long nanoTime;
		long duration;
		final ArrayList< Long > oldTimes = new ArrayList<>();
		final ArrayList< Long > newTimes = new ArrayList<>();

		for ( int repetition = 0; repetition < 10; repetition++ )
		{
			// Old way
			nanoTime = System.nanoTime();
			final StackView< ByteType > stackView = new StackView<>( getRandomAccessibleIntervals( numSlices, nx, ny ) );
			final RandomAccess< ByteType > access = stackView.randomAccess();
			for ( int i = 0; i < numSlices; i++ )
				access.setPositionAndGet( 0, 0, i );
			duration = System.nanoTime() - nanoTime;
			System.out.println( "Old DefaultRA [ns]: " + duration );
			oldTimes.add( duration );

			// New way
			nanoTime = System.nanoTime();
			final LazyStackView< ByteType > lazyStackView = new LazyStackView<>( getRandomAccessibleIntervals( numSlices, nx, ny ) );
			final RandomAccess< ByteType > lazyAccess = lazyStackView.randomAccess();
			for ( int i = 0; i < numSlices; i++ )
				lazyAccess.setPositionAndGet( 0, 0, i );
			duration = System.nanoTime() - nanoTime;
			System.out.println( "New DefaultRA [ns]: " + duration );
			newTimes.add( duration );
		}

		System.out.println( "Old average = " + oldTimes.stream().mapToDouble( x -> x ).summaryStatistics().getAverage() );
		System.out.println( "New average = " + newTimes.stream().mapToDouble( x -> x ).summaryStatistics().getAverage() );
	}

	private static ArrayList< RandomAccessibleInterval< ByteType > > getRandomAccessibleIntervals( int numSlices, int nx, int ny )
	{
		final ArrayList< RandomAccessibleInterval< ByteType> > rais = new ArrayList<>();
		for ( int i = 0; i < numSlices; i++ )
		{
			rais.add( ArrayImgs.bytes( nx, ny ) );
		}
		return rais;
	}
}
```

Output:
```
Old DefaultRA [ns]: 341932322
New DefaultRA [ns]: 49534316
Old DefaultRA [ns]: 53715032
New DefaultRA [ns]: 135685258
Old DefaultRA [ns]: 27748677
New DefaultRA [ns]: 210612767
Old DefaultRA [ns]: 10658957
New DefaultRA [ns]: 9818483
Old DefaultRA [ns]: 32998927
New DefaultRA [ns]: 8296665
Old DefaultRA [ns]: 9182600
New DefaultRA [ns]: 42703781
Old DefaultRA [ns]: 78796986
New DefaultRA [ns]: 7036566
Old DefaultRA [ns]: 12728417
New DefaultRA [ns]: 9498186
Old DefaultRA [ns]: 11396330
New DefaultRA [ns]: 30719648
Old DefaultRA [ns]: 8561321
New DefaultRA [ns]: 12746940
Old average = 5.87719569E7
New average = 5.1665261E7
```

Conclusion: This looks like as if there is no performance issue doing it the new way, for the tested access pattern.

@tpietzsch
I tried here to benchmark the LazyStackView. This seems to indicate that there is no performance issue.
Please let me know if you'd like me to test other access patterns.