strangedb-core/src/main/java/it/cavallium/strangedb/database/references/DatabaseReferencesMetadataCache.java

package it.cavallium.strangedb.database.references;

import it.cavallium.strangedb.VariableWrapper;
import it.unimi.dsi.fastutil.longs.*;
import it.unimi.dsi.fastutil.objects.ObjectArrayList;
import it.unimi.dsi.fastutil.objects.ObjectIterator;
import it.unimi.dsi.fastutil.objects.ObjectIterators;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.*;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import static it.cavallium.strangedb.database.IBlocksMetadata.ERROR_BLOCK_ID;
import static it.cavallium.strangedb.database.blocks.DatabaseBlocksMetadata.BLOCK_META_READS_AT_EVERY_READ;
import static it.cavallium.strangedb.database.references.DatabaseReferencesMetadata.NONEXISTENT_REFERENCE_INFO;
import static it.cavallium.strangedb.database.references.DatabaseReferencesMetadata.REF_META_READS_AT_EVERY_READ;

public class DatabaseReferencesMetadataCache {

	private static final int BASE_QUANTITY = (REF_META_READS_AT_EVERY_READ < 500 ? REF_META_READS_AT_EVERY_READ : 500);
	private static final int GOOD_CACHE_SIZE = 140 * BASE_QUANTITY;
	private static final int FLUSH_CACHE_SIZE = 300 * BLOCK_META_READS_AT_EVERY_READ;
	private static final int MAX_CACHE_SIZE = 400 * BASE_QUANTITY;

	private final Long2LongMap references2Blocks = Long2LongMaps.synchronize(new Long2LongLinkedOpenHashMap(MAX_CACHE_SIZE, 0.5f));
	private final Long2ByteMap referencesCleaners = Long2ByteMaps.synchronize(new Long2ByteLinkedOpenHashMap(MAX_CACHE_SIZE, 0.5f));
	private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(false);
	private final DatabaseReferencesMetadataCacheFlusher flusher;
	private volatile boolean closed;
	ExecutorService flushExecutorService = Executors.newFixedThreadPool(ForkJoinPool.getCommonPoolParallelism(), (r) -> new Thread(r, "References Flush Thread"));

	public DatabaseReferencesMetadataCache(DatabaseReferencesMetadataCacheFlusher flusher) {
		this.flusher = flusher;
	}

	public long getBlock(long reference) throws IOException {
		if (closed) throw new IOException("Cache already closed!");
		lock.readLock().lock();
		try {
			return references2Blocks.getOrDefault(reference, ERROR_BLOCK_ID);
		} finally {
			lock.readLock().unlock();
		}
	}

	public ReferenceInfo get(long reference) throws IOException {
		if (closed) throw new IOException("Cache already closed!");
		lock.readLock().lock();
		try {
			long blockId = references2Blocks.getOrDefault(reference, ERROR_BLOCK_ID);
			if (blockId == ERROR_BLOCK_ID) {
				return NONEXISTENT_REFERENCE_INFO;
			}
			byte cleanerId = referencesCleaners.get(reference);
			return new ReferenceInfo(cleanerId, blockId);
		} finally {
			lock.readLock().unlock();
		}
	}

	public void put(long reference, byte cleanerId, long blockId) throws IOException {
		if (closed) throw new IOException("Cache already closed!");
		lock.writeLock().lock();
		try {
			if (cleanerId == 0) {
				throw new IOException("Null cleaner id");
			}
			references2Blocks.put(reference, blockId);
			referencesCleaners.put(reference, cleanerId);
			flush();
		} finally {
			lock.writeLock().unlock();
		}
	}

	public void putAll(long[] references, byte[] cleanerIds, long[] blockIds) throws IOException {
		if (closed) throw new IOException("Cache already closed!");
		lock.writeLock().lock();
		try {
			Long2LongMap referencesBlocksToAdd = new Long2LongLinkedOpenHashMap(references, blockIds, 0.5f);
			Long2ByteMap referencesCleanersToAdd = new Long2ByteLinkedOpenHashMap(references, cleanerIds, 0.5f);
			for (int i = 0; i < references.length; i++) {
				if (cleanerIds[i] == 0) {
					referencesBlocksToAdd.remove(references[i]);
					referencesCleanersToAdd.remove(references[i]);
				}
			}
			references2Blocks.putAll(referencesBlocksToAdd);
			referencesCleaners.putAll(referencesCleanersToAdd);
			flush();
		} finally {
			lock.writeLock().unlock();
		}
	}

	private void flush() throws IOException {
		if (closed) return;
		int references2BlocksSize = references2Blocks.size();
		if (references2BlocksSize >= FLUSH_CACHE_SIZE) {
			ObjectIterator<Long2LongMap.Entry> entriesIterator = references2Blocks.long2LongEntrySet().iterator();
			ObjectIterator<Long2ByteMap.Entry> cleanersIterator = referencesCleaners.long2ByteEntrySet().iterator();
			@SuppressWarnings("unchecked")
			ObjectArrayList<Callable<Void>> tasks = ObjectArrayList.wrap(new Callable[references2BlocksSize - GOOD_CACHE_SIZE], references2BlocksSize - GOOD_CACHE_SIZE);
			for (int i = 0; i < references2BlocksSize - GOOD_CACHE_SIZE; i++) {
				Long2LongMap.Entry entry = entriesIterator.next();
				Long2ByteMap.Entry cleaner = cleanersIterator.next();
				long refId = entry.getLongKey();
				byte cleanerId = cleaner.getByteValue();
				long blockId = entry.getLongValue();
				entriesIterator.remove();
				cleanersIterator.remove();

				tasks.set(i, () -> {
					try {
						flusher.flush(refId, cleanerId, blockId);
					} catch (IOException e) {
						throw new CompletionException(e);
					}
					return null;
				});
			}
			try {
				flushExecutorService.invokeAll(tasks);
			} catch (InterruptedException e) {
				throw new IOException(e.getCause());
			}
		}
	}

	public void close() throws IOException {
		if (!closed) {
			closed = true;
			lock.writeLock().lock();
			try {
				int references2BlocksSize = references2Blocks.size();
				ObjectIterator<Long2LongMap.Entry> entriesIterator = references2Blocks.long2LongEntrySet().iterator();
				ObjectIterator<Long2ByteMap.Entry> cleanersIterator = referencesCleaners.long2ByteEntrySet().iterator();
				@SuppressWarnings("unchecked")
				ObjectArrayList<Callable<Void>> tasks = ObjectArrayList.wrap(new Callable[references2BlocksSize], references2BlocksSize);
				for (int i = 0; i < references2BlocksSize; i++) {
					Long2LongMap.Entry entry = entriesIterator.next();
					Long2ByteMap.Entry cleaner = cleanersIterator.next();
					long refId = entry.getLongKey();
					byte cleanerId = cleaner.getByteValue();
					long blockId = entry.getLongValue();
					entriesIterator.remove();
					cleanersIterator.remove();
					tasks.set(i, () -> {
						try {
							flusher.flush(refId, cleanerId, blockId);
						} catch (IOException e) {
							throw new CompletionException(e);
						}
						return null;
					});
				}
				try {
					flushExecutorService.invokeAll(tasks);
				} catch (InterruptedException e) {
					throw new IOException(e.getCause());
				}
				flushExecutorService.shutdown();
				try {
					if (!flushExecutorService.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS))
						flushExecutorService.shutdownNow();
				} catch (InterruptedException e) {
					throw new IOException(e);
				}
			} finally {
				lock.writeLock().unlock();
			}
		}
	}
}