statesystem/org.eclipse.tracecompass.statesystem.core/src/org/eclipse/tracecompass/internal/statesystem/core/backend/historytree/HistoryTreeFactory.java

   1 /*******************************************************************************
   2  * Copyright (c) 2016 École Polytechnique de Montréal
   3  *
   4  * All rights reserved. This program and the accompanying materials are
   5  * made available under the terms of the Eclipse Public License v1.0 which
   6  * accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *******************************************************************************/
   9
  10 package org.eclipse.tracecompass.internal.statesystem.core.backend.historytree;
  11
  12 import java.io.IOException;
  13 import java.nio.ByteBuffer;
  14 import java.nio.ByteOrder;
  15 import java.nio.channels.ReadableByteChannel;
  16 import java.nio.file.Files;
  17 import java.nio.file.Path;
  18 import java.nio.file.StandardOpenOption;
  19
  20 import org.eclipse.jdt.annotation.NonNullByDefault;
  21
  22 /**
  23  * Class that contains factory methods to build different types of history trees
  24  *
  25  * @author Geneviève Bastien
  26  */
  27 @NonNullByDefault
  28 public final class HistoryTreeFactory {
  29
  30     private HistoryTreeFactory() {
  31     }
  32
  33     /**
  34      * Create a new State History from scratch, using a {@link HTConfig} object
  35      * for configuration.
  36      *
  37      * @param conf
  38      *            The config to use for this History Tree.
  39      * @return the new state history tree
  40      * @throws IOException
  41      *             If an error happens trying to open/write to the file
  42      *             specified in the config
  43      */
  44     public static IHistoryTree createHistoryTree(HTConfig conf) throws IOException {
  45         return new HistoryTreeClassic(conf);
  46     }
  47
  48     /**
  49      * "Reader" factory : instantiate a SHTree from an existing tree file on
  50      * disk
  51      *
  52      * @param existingStateFile
  53      *            Path/filename of the history-file we are to open
  54      * @param expectedProviderVersion
  55      *            The expected version of the state provider
  56      * @return The history tree
  57      * @throws IOException
  58      *             If an error happens reading the file
  59      */
  60     public static IHistoryTree createFromFile(Path existingStateFile, int expectedProviderVersion) throws IOException {
  61         /*
  62          * Check the file exists and has a positive length. These verifications
  63          * will also be done in the HT's constructor.
  64          */
  65         if (!Files.isReadable(existingStateFile)) {
  66             throw new IOException("Selected state file does not exist or is not readable."); //$NON-NLS-1$
  67         }
  68         if (Files.size(existingStateFile) <= 0) {
  69             throw new IOException("Empty target file"); //$NON-NLS-1$
  70         }
  71
  72         /* Read the magic number from the history tree file */
  73         ByteBuffer buffer = ByteBuffer.allocate(Integer.BYTES);
  74         try (ReadableByteChannel channel = Files.newByteChannel(existingStateFile, StandardOpenOption.READ);) {
  75             buffer.order(ByteOrder.LITTLE_ENDIAN);
  76             buffer.clear();
  77             channel.read(buffer);
  78             buffer.flip();
  79         }
  80
  81         /*
  82          * Check the magic number to see which history tree class to create
  83          */
  84         int magicNumber = buffer.getInt();
  85         switch (magicNumber) {
  86         case HistoryTreeClassic.HISTORY_FILE_MAGIC_NUMBER:
  87             return new HistoryTreeClassic(existingStateFile.toFile(), expectedProviderVersion);
  88         default:
  89             throw new IOException("Not a known history tree file"); //$NON-NLS-1$
  90         }
  91     }
  92 }