Examples of eu.stratosphere.nephele.services.iomanager.BlockChannelReader

Package eu.stratosphere.nephele.services.iomanager

Examples of eu.stratosphere.nephele.services.iomanager.BlockChannelReader

eu.stratosphere.nephele.services.iomanager.BlockChannelReader
A reader that reads data in blocks from a file channel. The reader reads the blocks into a {@link eu.stratosphere.core.memory.MemorySegment} in an asynchronous fashion. That is, a readrequest is not processed by the thread that issues it, but by an asynchronous reader thread. Once the read request is done, the asynchronous reader adds the full MemorySegment to a return queue where it can be popped by the worker thread, once it needs the data. The return queue is in this case a {@link java.util.concurrent.LinkedBlockingQueue}, such that the working thread blocks until the request has been served, if the request is still pending when the it requires the data.
Typical pre-fetching reads are done by issuing the read requests early and popping the return queue once the data is actually needed.
The reader has no notion whether the size of the memory segments is actually the size of the blocks on disk, or even whether the file was written in blocks of the same size, or in blocks at all. Ensuring that the writing and reading is consistent with each other (same blocks sizes) is up to the programmer.

      // first set up the reader with some memory.
      final List<MemorySegment> segments = new ArrayList<MemorySegment>(2);
      segments.add(getNextBuffer());
      segments.add(getNextBuffer());
      
      final BlockChannelReader inReader = this.ioManager.createBlockChannelReader(p.getBuildSideChannel().getChannelID());
      final ChannelReaderInputView inView = new HeaderlessChannelReaderInputView(inReader, segments,
            p.getBuildSideBlockCount(), p.getLastSegmentLimit(), false);
      final ChannelReaderInputViewIterator<BT> inIter = new ChannelReaderInputViewIterator<BT>(inView, 
          this.availableMemory, this.buildSideSerializer);
      final TypeComparator<BT> btComparator = this.buildSideComparator;

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      for (int i = 0; i < channelIDs.size(); i++) {
        final ChannelWithBlockCount channel = channelIDs.get(i);
        final List<MemorySegment> segsForChannel = inputSegments.get(i);
        
        // create a reader. if there are multiple segments for the reader, issue multiple together per I/O request
        final BlockChannelReader reader = segsForChannel.size() >= 4 ? 
          this.ioManager.createBlockChannelReader(channel.getChannel(), segsForChannel.size() / 2) :
          this.ioManager.createBlockChannelReader(channel.getChannel());
          
        readerList.add(reader);
        registerOpenChannelToBeRemovedAtShudown(reader);

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        numBuffersSpilled += toSpill;
      }


      // now close the writer and create the reader
      currentWriter.close();
      final BlockChannelReader reader = ioManager.createBlockChannelReader(currentWriter.getChannelID());


      // gather some memory segments to circulate while reading back the data
      final ArrayList<MemorySegment> readSegments = new ArrayList<MemorySegment>();
      try {
        while (readSegments.size() < minBuffersForSpilledReadEnd) {
          readSegments.add(emptyBuffers.take());
        }


        // read the first segment
        MemorySegment firstSeg = readSegments.remove(readSegments.size() - 1);
        reader.readBlock(firstSeg);
        firstSeg = reader.getReturnQueue().take();


        // create the read end reading one less buffer, because the first buffer is already read back
        readEnd = new ReadEnd(firstSeg, emptyBuffers, fullBuffers, reader, readSegments, segmentSize,
          numBuffersSpilled - 1);
      } catch (InterruptedException e) {

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, NUM_MEMORY_SEGMENTS);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, outView.getBlockCount(), true);
    generator.reset();
    
    // read and re-generate all records and compare them
    final Record readRec = new Record();
    for (int i = 0; i < NUM_PAIRS_SHORT; i++) {
      generator.next(rec);
      readRec.read(inView);
      
      Key k1 = rec.getField(0, Key.class);
      Value v1 = rec.getField(1, Value.class);
      
      Key k2 = readRec.getField(0, Key.class);
      Value v2 = readRec.getField(1, Value.class);
      
      Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, NUM_MEMORY_SEGMENTS);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, outView.getBlockCount(), true);
    generator.reset();
    
    // read and re-generate all records and compare them
    final Record readRec = new Record();
    for (int i = 0; i < NUM_PAIRS_LONG; i++) {
      generator.next(rec);
      readRec.read(inView);
      final Key k1 = rec.getField(0, Key.class);
      final Value v1 = rec.getField(1, Value.class);
      final Key k2 = readRec.getField(0, Key.class);
      final Value v2 = readRec.getField(1, Value.class);
      Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, NUM_MEMORY_SEGMENTS);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, outView.getBlockCount(), true);
    generator.reset();
    
    // read and re-generate all records and compare them
    try {
      final Record readRec = new Record();
      for (int i = 0; i < NUM_PAIRS_SHORT + 1; i++) {
        generator.next(rec);
        readRec.read(inView);
        final Key k1 = rec.getField(0, Key.class);
        final Value v1 = rec.getField(1, Value.class);
        final Key k2 = readRec.getField(0, Key.class);
        final Value v2 = readRec.getField(1, Value.class);
        Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
      }
      Assert.fail("Expected an EOFException which did not occur.");
    }
    catch (EOFException eofex) {
      // expected
    }
    catch (Throwable t) {
      // unexpected
      Assert.fail("Unexpected Exception: " + t.getMessage());
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, NUM_MEMORY_SEGMENTS);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, true);
    generator.reset();
    
    // read and re-generate all records and cmpare them
    final Record readRec = new Record();
    for (int i = 0; i < NUM_PAIRS_SHORT; i++) {
      generator.next(rec);
      readRec.read(inView);
      
      Key k1 = rec.getField(0, Key.class);
      Value v1 = rec.getField(1, Value.class);
      
      Key k2 = readRec.getField(0, Key.class);
      Value v2 = readRec.getField(1, Value.class);
      
      Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, 1);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, outView.getBlockCount(), true);
    generator.reset();
    
    // read and re-generate all records and compare them
    final Record readRec = new Record();
    for (int i = 0; i < NUM_PAIRS_SHORT; i++) {
      generator.next(rec);
      readRec.read(inView);
      
      Key k1 = rec.getField(0, Key.class);
      Value v1 = rec.getField(1, Value.class);
      
      Key k2 = readRec.getField(0, Key.class);
      Value v2 = readRec.getField(1, Value.class);
      
      Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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    }
    this.memoryManager.release(outView.close());
    
    // create the reader input view
    memory = this.memoryManager.allocatePages(this.parentTask, NUM_MEMORY_SEGMENTS);
    final BlockChannelReader reader = this.ioManager.createBlockChannelReader(channel);
    final ChannelReaderInputView inView = new ChannelReaderInputView(reader, memory, outView.getBlockCount(), true);
    generator.reset();
    
    // read and re-generate all records and compare them
    final Record readRec = new Record();
    for (int i = 0; i < NUM_PAIRS_SHORT / 2; i++) {
      generator.next(rec);
      readRec.read(inView);
      
      Key k1 = rec.getField(0, Key.class);
      Value v1 = rec.getField(1, Value.class);
      
      Key k2 = readRec.getField(0, Key.class);
      Value v2 = readRec.getField(1, Value.class);
      
      Assert.assertTrue("The re-generated and the read record do not match.", k1.equals(k2) && v1.equals(v2));
    }
    
    this.memoryManager.release(inView.close());
    reader.deleteChannel();
  }

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      // recollect memory from a previous view
      if (this.externalInView != null) {
        this.externalInView.close();
      }
      
      final BlockChannelReader reader = this.ioManager.createBlockChannelReader(this.writer.getChannelID());
      this.externalInView = new HeaderlessChannelReaderInputView(reader, this.fullSegments, this.blockCount, this.numBytesInLastSegment, false);
      return this.externalInView;
    }
  }

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