Class ScratchFile

java.lang.Object
org.apache.pdfbox.io.ScratchFile
All Implemented Interfaces:
Closeable, AutoCloseable

public class ScratchFile extends Object implements Closeable
Implements a memory page handling mechanism as base for creating (multiple) RandomAccess buffers each having its set of pages (implemented by ScratchFileBuffer). A buffer is created calling createBuffer().

Pages can be stored in main memory or in a temporary file. A mixed mode is supported storing a certain amount of pages in memory and only the additional ones in temporary file (defined by maximum main memory to be used).

Pages can be marked as 'free' in order to re-use them. For in-memory pages this will release the used memory while for pages in temporary file this simply marks the area as free to re-use.

If a temporary file was created (done with the first page to be stored in temporary file) it is deleted when close() is called.

Using this class for RandomAccess buffers allows for a direct control on the maximum memory usage and allows processing large files for which we otherwise would get an OutOfMemoryError in case of using RandomAccessBuffer.

This base class for providing pages is thread safe (the buffer implementations are not).

  • Field Details

    • LOG

      private static final org.apache.commons.logging.Log LOG
    • ENLARGE_PAGE_COUNT

      private static final int ENLARGE_PAGE_COUNT
      number of pages by which we enlarge the scratch file (reduce I/O-operations)
      See Also:
    • INIT_UNRESTRICTED_MAINMEM_PAGECOUNT

      private static final int INIT_UNRESTRICTED_MAINMEM_PAGECOUNT
      in case of unrestricted main memory usage this is the initial number of pages inMemoryPages is setup for
      See Also:
    • PAGE_SIZE

      private static final int PAGE_SIZE
      See Also:
    • ioLock

      private final Object ioLock
    • scratchFileDirectory

      private final File scratchFileDirectory
    • file

      private File file
      scratch file; only to be accessed under synchronization of ioLock
    • raf

      private RandomAccessFile raf
      random access to scratch file; only to be accessed under synchronization of ioLock
    • pageCount

      private volatile int pageCount
    • freePages

      private final BitSet freePages
    • inMemoryPages

      private volatile byte[][] inMemoryPages
      holds pointers to in-memory page content; will be initialized once in case of restricted main memory, otherwise it is enlarged as needed and first initialized to a size of INIT_UNRESTRICTED_MAINMEM_PAGECOUNT
    • inMemoryMaxPageCount

      private final int inMemoryMaxPageCount
    • maxPageCount

      private final int maxPageCount
    • useScratchFile

      private final boolean useScratchFile
    • maxMainMemoryIsRestricted

      private final boolean maxMainMemoryIsRestricted
    • buffers

      private final List<ScratchFileBuffer> buffers
    • isClosed

      private volatile boolean isClosed
  • Constructor Details

    • ScratchFile

      public ScratchFile(File scratchFileDirectory) throws IOException
      Initializes page handler. If a scratchFileDirectory is supplied, then the scratch file will be created in that directory.

      All pages will be stored in the scratch file.

      Parameters:
      scratchFileDirectory - The directory in which to create the scratch file or null to created it in the default temporary directory.
      Throws:
      IOException - If scratch file directory was given but don't exist.
    • ScratchFile

      public ScratchFile(MemoryUsageSetting memUsageSetting) throws IOException
      Initializes page handler. If a scratchFileDirectory is supplied, then the scratch file will be created in that directory.

      Depending on the size of allowed memory usage a number of pages (memorySize/PAGE_SIZE) will be stored in-memory and only additional pages will be written to/read from scratch file.

      Parameters:
      memUsageSetting - set how memory/temporary files are used for buffering streams etc.
      Throws:
      IOException - If scratch file directory was given but don't exist.
  • Method Details

    • getMainMemoryOnlyInstance

      public static ScratchFile getMainMemoryOnlyInstance()
      Getter for an instance using only unrestricted main memory for buffering (same as new ScratchFile(MemoryUsageSetting.setupMainMemoryOnly())).
      Returns:
      instance configured to only use main memory with no size restriction
    • getNewPage

      int getNewPage() throws IOException
      Returns a new free page, either from free page pool or by enlarging scratch file (may be created).
      Returns:
      index of new page
      Throws:
      IOException
    • enlarge

      private void enlarge() throws IOException
      This will provide new free pages by either enlarging the scratch file by a number of pages defined by ENLARGE_PAGE_COUNT - in case scratch file usage is allowed - or increase the inMemoryPages array in case main memory was not restricted. If neither of both is allowed/the case than free pages count won't be changed. The same is true if no new pages could be added because we reached the maximum of Integer.MAX_VALUE pages.

      If scratch file usage is allowed and scratch file does not exist already it will be created.

      Only to be called under synchronization on freePages.

      Throws:
      IOException
    • getPageSize

      int getPageSize()
      Returns byte size of a page.
      Returns:
      byte size of a page
    • readPage

      byte[] readPage(int pageIdx) throws IOException
      Reads the page with specified index.
      Parameters:
      pageIdx - index of page to read
      Returns:
      byte array of size PAGE_SIZE filled with page data read from file
      Throws:
      IOException
    • writePage

      void writePage(int pageIdx, byte[] page) throws IOException
      Writes updated page. Page is either kept in-memory if pageIdx < inMemoryMaxPageCount or is written to scratch file.

      Provided page byte array must not be re-used for other pages since we store it as is in case of in-memory handling.

      Parameters:
      pageIdx - index of page to write
      page - page to write (length has to be 4096)
      Throws:
      IOException - in case page index is out of range or page has wrong length or writing to file failed
    • checkClosed

      void checkClosed() throws IOException
      Checks if this page handler has already been closed. If so, an IOException is thrown.
      Throws:
      IOException - If close() has already been called.
    • createBuffer

      public RandomAccess createBuffer() throws IOException
      Creates a new buffer using this page handler.
      Returns:
      A new buffer.
      Throws:
      IOException - If an error occurred.
    • removeBuffer

      void removeBuffer(ScratchFileBuffer buffer)
    • createBuffer

      public RandomAccess createBuffer(InputStream input) throws IOException
      Creates a new buffer using this page handler and initializes it with the data read from provided input stream (input stream is copied to buffer). The buffer data pointer is reset to point to first byte.
      Parameters:
      input - The input stream that is to be copied into the buffer.
      Returns:
      A new buffer containing data read from input stream.
      Throws:
      IOException - If an error occurred.
    • markPagesAsFree

      void markPagesAsFree(int[] pageIndexes, int off, int count)
      Allows a buffer which is cleared/closed to release its pages to be re-used.
      Parameters:
      pageIndexes - pages indexes of pages to release
      count - number of page indexes contained in provided array
    • close

      public void close() throws IOException
      Closes and deletes the temporary file. No further interaction with the scratch file or associated buffers can happen after this method is called. It also releases in-memory pages.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Throws:
      IOException - If there was a problem closing or deleting the temporary file.