Example usage for org.apache.hadoop.hdfs.shortcircuit ClientMmap getMappedByteBuffer

Introduction

In this page you can find the example usage for org.apache.hadoop.hdfs.shortcircuit ClientMmap getMappedByteBuffer.

Prototype

public MappedByteBuffer getMappedByteBuffer() 

Source Link

Usage

From source file:com.mellanox.r4h.DFSInputStream.java

License:Apache License

private synchronized ByteBuffer tryReadZeroCopy(int maxLength, EnumSet<ReadOption> opts) throws IOException {
    // Copy 'pos' and 'blockEnd' to local variables to make it easier for the
    // JVM to optimize this function.
    final long curPos = pos;
    final long curEnd = blockEnd;
    final long blockStartInFile = currentLocatedBlock.getStartOffset();
    final long blockPos = curPos - blockStartInFile;

    // Shorten this read if the end of the block is nearby.
    long length63;
    if ((curPos + maxLength) <= (curEnd + 1)) {
        length63 = maxLength;// www .  j a  v  a2 s  .  c  o  m
    } else {
        length63 = 1 + curEnd - curPos;
        if (length63 <= 0) {
            if (DFSClient.LOG.isDebugEnabled()) {
                DFSClient.LOG.debug("Unable to perform a zero-copy read from offset " + curPos + " of " + src
                        + "; " + length63 + " bytes left in block.  " + "blockPos=" + blockPos + "; curPos="
                        + curPos + "; curEnd=" + curEnd);
            }
            return null;
        }
        if (DFSClient.LOG.isDebugEnabled()) {
            DFSClient.LOG.debug("Reducing read length from " + maxLength + " to " + length63
                    + " to avoid going more than one byte " + "past the end of the block.  blockPos=" + blockPos
                    + "; curPos=" + curPos + "; curEnd=" + curEnd);
        }
    }
    // Make sure that don't go beyond 31-bit offsets in the MappedByteBuffer.
    int length;
    if (blockPos + length63 <= Integer.MAX_VALUE) {
        length = (int) length63;
    } else {
        long length31 = Integer.MAX_VALUE - blockPos;
        if (length31 <= 0) {
            // Java ByteBuffers can't be longer than 2 GB, because they use
            // 4-byte signed integers to represent capacity, etc.
            // So we can't mmap the parts of the block higher than the 2 GB offset.
            // FIXME: we could work around this with multiple memory maps.
            // See HDFS-5101.
            if (DFSClient.LOG.isDebugEnabled()) {
                DFSClient.LOG.debug("Unable to perform a zero-copy read from offset " + curPos + " of " + src
                        + "; 31-bit MappedByteBuffer limit " + "exceeded.  blockPos=" + blockPos + ", curEnd="
                        + curEnd);
            }
            return null;
        }
        length = (int) length31;
        if (DFSClient.LOG.isDebugEnabled()) {
            DFSClient.LOG.debug(
                    "Reducing read length from " + maxLength + " to " + length + " to avoid 31-bit limit.  "
                            + "blockPos=" + blockPos + "; curPos=" + curPos + "; curEnd=" + curEnd);
        }
    }
    final ClientMmap clientMmap = blockReader.getClientMmap(opts);
    if (clientMmap == null) {
        if (DFSClient.LOG.isDebugEnabled()) {
            DFSClient.LOG.debug("unable to perform a zero-copy read from offset " + curPos + " of " + src
                    + "; BlockReader#getClientMmap returned " + "null.");
        }
        return null;
    }
    boolean success = false;
    ByteBuffer buffer;
    try {
        seek(curPos + length);
        buffer = clientMmap.getMappedByteBuffer().asReadOnlyBuffer();
        buffer.position((int) blockPos);
        buffer.limit((int) (blockPos + length));
        getExtendedReadBuffers().put(buffer, clientMmap);
        synchronized (infoLock) {
            readStatistics.addZeroCopyBytes(length);
        }
        if (DFSClient.LOG.isDebugEnabled()) {
            DFSClient.LOG.debug("readZeroCopy read " + length + " bytes from offset " + curPos
                    + " via the zero-copy read " + "path.  blockEnd = " + blockEnd);
        }
        success = true;
    } finally {
        if (!success) {
            IOUtils.closeQuietly(clientMmap);
        }
    }
    return buffer;
}

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