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本文主要研究一下Elasticsearch的Releasables
Releasable
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/common/lease/Releasable.java
public interface Releasable extends Closeable { @Override void close();}- Releasable继承了java.io.Closeable接口
Releasables
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/common/lease/Releasables.java
public enum Releasables { ; private static void close(Iterable<? extends Releasable> releasables, boolean ignoreException) { try { // this does the right thing with respect to add suppressed and not wrapping errors etc. IOUtils.close(releasables); } catch (IOException e) { if (ignoreException == false) { throw new UncheckedIOException(e); } } } /** Release the provided {@link Releasable}s. */ public static void close(Iterable<? extends Releasable> releasables) { close(releasables, false); } /** Release the provided {@link Releasable}s. */ public static void close(Releasable... releasables) { close(Arrays.asList(releasables)); } /** Release the provided {@link Releasable}s, ignoring exceptions. */ public static void closeWhileHandlingException(Iterable<Releasable> releasables) { close(releasables, true); } /** Release the provided {@link Releasable}s, ignoring exceptions. */ public static void closeWhileHandlingException(Releasable... releasables) { closeWhileHandlingException(Arrays.asList(releasables)); } /** Release the provided {@link Releasable}s, ignoring exceptions if <code>success</code> is {@code false}. */ public static void close(boolean success, Iterable<Releasable> releasables) { if (success) { close(releasables); } else { closeWhileHandlingException(releasables); } } /** Release the provided {@link Releasable}s, ignoring exceptions if <code>success</code> is {@code false}. */ public static void close(boolean success, Releasable... releasables) { close(success, Arrays.asList(releasables)); } /** Wrap several releasables into a single one. This is typically useful for use with try-with-resources: for example let's assume * that you store in a list several resources that you would like to see released after execution of the try block: * * <pre> * List<Releasable> resources = ...; * try (Releasable releasable = Releasables.wrap(resources)) { * // do something * } * // the resources will be released when reaching here * </pre> */ public static Releasable wrap(final Iterable<Releasable> releasables) { return () -> close(releasables); } /** @see #wrap(Iterable) */ public static Releasable wrap(final Releasable... releasables) { return () -> close(releasables); } /** * Equivalent to {@link #wrap(Releasable...)} but can be called multiple times without double releasing. */ public static Releasable releaseOnce(final Releasable... releasables) { final AtomicBoolean released = new AtomicBoolean(false); return () -> { if (released.compareAndSet(false, true)) { close(releasables); } }; }}- Releasables提供close、closeWhileHandlingException、wrap、releaseOnce静态方法用于更方便地使用Releasable
实例
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/index/translog/Translog.java
public class Translog extends AbstractIndexShardComponent implements IndexShardComponent, Closeable { //...... public static void writeOperations(StreamOutput outStream, List<Operation> toWrite) throws IOException { final ReleasableBytesStreamOutput out = new ReleasableBytesStreamOutput(BigArrays.NON_RECYCLING_INSTANCE); try { outStream.writeInt(toWrite.size()); final BufferedChecksumStreamOutput checksumStreamOutput = new BufferedChecksumStreamOutput(out); for (Operation op : toWrite) { out.reset(); final long start = out.position(); out.skip(Integer.BYTES); writeOperationNoSize(checksumStreamOutput, op); long end = out.position(); int operationSize = (int) (out.position() - Integer.BYTES - start); out.seek(start); out.writeInt(operationSize); out.seek(end); ReleasablePagedBytesReference bytes = out.bytes(); bytes.writeTo(outStream); } } finally { Releasables.close(out); } } //......}- writeOperations在finally中使用Releasables.close关闭了ReleasableBytesStreamOutput
小结
Releasables提供close、closeWhileHandlingException、wrap、releaseOnce静态方法用于更方便地使用Releasable
doc
- Releasables