聊聊Elasticsearch的Releasables

摘要：序本文主要研究一下的继承了接口提供静态方法用于更方便地使用实例在中使用关闭了小结提供静态方法用于更方便地使用

本文主要研究一下Elasticsearch的Releasables

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

elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/common/lease/Releasables.java

public enum Releasables {
    ;

    private static void close(Iterable 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 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 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 success is {@code false}. */
    public static void close(boolean success, Iterable releasables) {
        if (success) {
            close(releasables);
        } else {
            closeWhileHandlingException(releasables);
        }
    }

    /** Release the provided {@link Releasable}s, ignoring exceptions if success 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:
     *
     *  
     *  List resources = ...;
     *  try (Releasable releasable = Releasables.wrap(resources)) {
     *      // do something
     *  }
     *  // the resources will be released when reaching here
     *  
     */
    public static Releasable wrap(final Iterable 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

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 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

Releasables提供close、closeWhileHandlingException、wrap、releaseOnce静态方法用于更方便地使用Releasable

Releasables