Package io.pravega.client.segment.impl

Interface EventSegmentReader

  • All Superinterfaces:
    java.lang.AutoCloseable
    public interface EventSegmentReader
extends java.lang.AutoCloseable
    Defines an event reader for a single segment. Once created a offset may be provided by calling setOffset if the application does not want to read from offset 0. The next read will proceed from this offset. Subsequent reads will read from where the previous read call on this instance left off. (Parallel calls to read data will be serialized) Get offset can be used to store a location to revert back to that position in the future.

    • Method Summary

      All Methods Instance Methods Abstract Methods Default Methods 
      Modifier and Type Method Description
      void close()
      Closes this reader.
      java.util.concurrent.CompletableFuture<?> fillBuffer()
      Issues a request to asynchronously fill up the buffer.
      long getOffset()
      Gets the current offset.
      Segment getSegmentId()  
      boolean isSegmentReady()
      Returns true if read() can be invoked without blocking.
      default java.nio.ByteBuffer read()
      Reads the bytes of a single event from the segment.
      java.nio.ByteBuffer read​(long firstByteTimeoutMillis)
      Reads bytes of a single event from the segment.
      default void setOffset​(long offset)
      Sets the offset for reading from the segment.
      void setOffset​(long offset, boolean resendRequest)
      Sets the offset for reading from the segment.

    • Method Detail

      • getSegmentId

        Segment getSegmentId()

      • setOffset

        default void setOffset​(long offset)
        Sets the offset for reading from the segment.
        Parameters:
        offset - The offset to set.

      • setOffset

        void setOffset​(long offset,
               boolean resendRequest)
        Sets the offset for reading from the segment.
        Parameters:
        offset - The offset to set.
        resendRequest - Resend the read request incase there is an already pending read request for the offset.

      • getOffset

        long getOffset()
        Gets the current offset. (Passing this to setOffset in the future will reset reads to the current position in the segment.)
        Returns:
        The current offset.

      • read

        default java.nio.ByteBuffer read()
                          throws EndOfSegmentException,
                                 SegmentTruncatedException
        Reads the bytes of a single event from the segment. Buffering is performed internally to try to prevent blocking. If there is no event after timeout, then it returns null. EndOfSegmentException indicates the segment has ended and there are no more events to read.
        Returns:
        A ByteBuffer containing the serialized data that was written via EventStreamWriter.writeEvent(String, Object)
        Throws:
        EndOfSegmentException - If no event could be read because the end of the segment was reached.
        SegmentTruncatedException - If the segment has been truncated beyond the current offset and the data cannot be read.

      • read

        java.nio.ByteBuffer read​(long firstByteTimeoutMillis)
                  throws EndOfSegmentException,
                         SegmentTruncatedException
        Reads bytes of a single event from the segment. Buffering is performed internally to try to prevent blocking. If there is no event after timeout, then it returns null. EndOfSegmentException indicates the segment has ended and there are no more events to read. A timeout can be provided that will be used to determine how long to block obtaining the first byte of an event. If this timeout elapses, then null is returned. Once an event has been partially read, it will be fully read without regard to the timeout.
        Parameters:
        firstByteTimeoutMillis - The maximum length of time to block to get the first byte of the event.
        Returns:
        A ByteBuffer containing the serialized data that was written via EventStreamWriter.writeEvent(String, Object)
        Throws:
        EndOfSegmentException - If no event could be read because the end of the segment was reached.
        SegmentTruncatedException - If the segment has been truncated beyond the current offset and the data cannot be read.

      • fillBuffer

        java.util.concurrent.CompletableFuture<?> fillBuffer()
        Issues a request to asynchronously fill up the buffer. The goal is to prevent future read() calls from blocking. Calling this multiple times is harmless.
        Returns:
        A future that completes when the request to fill the buffer has returned.

      • close

        void close()
        Closes this reader. No further methods may be called after close. This will free any resources associated with the reader.
        Specified by:
        close in interface java.lang.AutoCloseable

      • isSegmentReady

        boolean isSegmentReady()
        Returns true if read() can be invoked without blocking. (This may be because there is data in a buffer, or the call will throw EndOfSegmentException).
        Returns:
        False if data read is blocking.