正在同步和IO文件

Question

我有一個使用位於特定目錄中的索引的方法。

public class TestSearchEngine implements SearchEngine<Tag> { 

private static final String INDEX_PATH = "/test/index"; 

private Directory directory; 
@Inject private TagDAO tagDAO; 
private int organizationId; 

@Override 
public void add(Tag tag) { 
    IndexWriterConfig indexWriterConfig = new IndexWriterConfig(Version.LUCENE_35, new StandardAnalyzer(Version.LUCENE_35));   
    IndexWriter indexWriter = getIndexWriter(indexWriterConfig); 

    //Create document 
    Document document = new Document(); 
    document.add(new Field("id", String.valueOf(tag.getId()), Field.Store.YES, Field.Index.NOT_ANALYZED)); 
    document.add(new Field("title", tag.getTitle(), Field.Store.NO, Field.Index.ANALYZED)); 

    try { 
     indexWriter.addDocument(document); 
     indexWriter.close(); 
    } catch (CorruptIndexException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

@Override 
public synchronized void setDirectory(int organizationId) throws IOException { 
    this.organizationId = organizationId; 
    File path = new File(INDEX_PATH + "/" + String.valueOf(organizationId)); 

    //If path does not exist, create it and create new index for organization 
    if(!path.exists()) { 
     path.mkdirs(); 
     buildCompleteIndex(organizationId, false); 
    } 

    this.directory = FSDirectory.open(path); //Open directory 
} 

private void buildCompleteIndex(int organizationId, boolean rebuildDir) { 
    if(rebuildDir) { 
     File path = new File(INDEX_PATH + "/" + String.valueOf(organizationId)); 
     try { 
      Utils.deleteDirectory(path); 
     } catch (IOException e) { 
      throw new LuceneIndexException("Error rebuilding index directory.", e); 
     } 
     path.mkdirs(); 
    } 

    List<Tag> tagList = tagDAO.findAll(organizationId); 
    for(Tag tag : tagList) { 
     add(tag); 
    } 
} 

private IndexReader getIndexReader() { 
    try { 
     return IndexReader.open(directory); 
    } catch (CorruptIndexException e) { 
     buildCompleteIndex(organizationId, true); 
    } catch (IOException e) { 
     throw new LuceneIndexException("IOException prevented IndexReader from opening Index.", e); 
    } catch(NullPointerException e) { 
     throw new LuceneIndexException("Index resource not available.", e); 
    } 
    return null; 
} 

}

在某些情況下，我趕上如果出於某種原因該指數成爲腐敗的一個例外，或者它只是已尚未創建。在這種情況下，將調用buildCompleteIndex（）方法，該方法刪除目錄並從數據源重新創建索引。

在多線程環境中，如何防止另一個線程創建類的實例，並使用調用該目錄時刪除或正在重建的方法？ setDirectory（）方法必須在任何其他方法工作之前調用，所以我假設在該方法上設置同步會解決這個問題，但是如果在線程已經存在的情況下該目錄變爲破壞，那麼它將如何開始調用重建方法在同一時間？換句話說，我對在多線程環境中刪除和更新IO文件的正確方法有點困惑。一些建議，將不勝感激。

Answer 1

回顧你的代碼，你已經在setDirectory（）上同步了。對於使用該特定實例的所有線程，它將阻塞，直到該方法完成。這包括buildCompleteIndex。如果你有創建這個類的新實例的線程，那麼你需要同步其他東西。例如，你可以同步一個靜態實例。

對文件和/或文件夾進行同步可能會變得非常複雜，特別是在運行多個環境（即JDK）的情況下。

像下面這樣，如果我理解你的問題可能的工作：

public class TestSearchEngine implements SearchEngine<Tag> { 

private static final String INDEX_PATH = "/test/index"; 

private Directory directory; 
@Inject private TagDAO tagDAO; 
private int organizationId; 

private static final Object mutex = new Object(); 

@Override 
public void add(Tag tag) { 
    IndexWriterConfig indexWriterConfig = new IndexWriterConfig(Version.LUCENE_35, new StandardAnalyzer(Version.LUCENE_35));   
    IndexWriter indexWriter = getIndexWriter(indexWriterConfig); 

    //Create document 
    Document document = new Document(); 
    document.add(new Field("id", String.valueOf(tag.getId()), Field.Store.YES, Field.Index.NOT_ANALYZED)); 
    document.add(new Field("title", tag.getTitle(), Field.Store.NO, Field.Index.ANALYZED)); 

    try { 
     indexWriter.addDocument(document); 
     indexWriter.close(); 
    } catch (CorruptIndexException e) { 
     e.printStackTrace(); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
} 

@Override 
public void setDirectory(int organizationId) throws IOException { 

     synchronized (mutex) { 
     this.organizationId = organizationId; 
     File path = new File(INDEX_PATH + "/" + String.valueOf(organizationId)); 

     //If path does not exist, create it and create new index for organization 
     if(!path.exists()) { 
      path.mkdirs(); 
      buildCompleteIndex(organizationId, false); 
     } 

     this.directory = FSDirectory.open(path); //Open directory 
     } 
} 

private void buildCompleteIndex(int organizationId, boolean rebuildDir) { 
    if(rebuildDir) { 
     File path = new File(INDEX_PATH + "/" + String.valueOf(organizationId)); 
     try { 
      Utils.deleteDirectory(path); 
     } catch (IOException e) { 
      throw new LuceneIndexException("Error rebuilding index directory.", e); 
     } 
     path.mkdirs(); 
    } 

    List<Tag> tagList = tagDAO.findAll(organizationId); 
    for(Tag tag : tagList) { 
     add(tag); 
    } 
} 

private IndexReader getIndexReader() { 
    try { 
     return IndexReader.open(directory); 
    } catch (CorruptIndexException e) { 
     buildCompleteIndex(organizationId, true); 
    } catch (IOException e) { 
     throw new LuceneIndexException("IOException prevented IndexReader from opening Index.", e); 
    } catch(NullPointerException e) { 
     throw new LuceneIndexException("Index resource not available.", e); 
    } 
    return null; 
} 

Answer 2

的IndexWriter已經是線程安全的，所以你如果有可能使用不同的線程相同的實例。

如果不是，請考慮在單個線程中執行所有索引操作。它很容易做到使用java ExecutorService。