Package com.graphhopper.storage

Class MMapDataAccess

java.lang.Object
com.graphhopper.storage.AbstractDataAccess
com.graphhopper.storage.MMapDataAccess
All Implemented Interfaces:
DataAccess, Closeable, AutoCloseable
public final class MMapDataAccess extends AbstractDataAccess
A DataAccess implementation using a memory-mapped file, i.e. a facility of the operating system to access a file like an area of RAM.

Java presents the mapped memory as a ByteBuffer, and ByteBuffer is not thread-safe, which means that access to a ByteBuffer must be externally synchronized.

This class itself is intended to be as thread-safe as other DataAccess implementations are.

The exact behavior of memory-mapping is reported to be wildly platform-dependent.

Author:
Peter Karich, Michael Zilske

  • Method Details

    • cleanMappedByteBuffer

      public static void cleanMappedByteBuffer(ByteBuffer buffer)

    • create

      public MMapDataAccess create(long bytes)
      Description copied from interface: DataAccess
      The first time you use a DataAccess object after configuring it you need to call this method. After that first call you have to use ensureCapacity to ensure that enough space is reserved.

    • ensureCapacity

      public boolean ensureCapacity(long bytes)
      Description copied from interface: DataAccess
      Ensures that the capacity of this object is at least the specified bytes. The first time you have to call 'create' instead.

      Returns:
      true if size was increased
      See Also:

    • loadExisting

      public boolean loadExisting()
      Returns:
      true if successfully loaded from persistent storage.

    • flush

      public void flush()
      Description copied from interface: DataAccess
      This method makes sure that the underlying data is written to the storage. Keep in mind that a disc normally has an IO cache so that flush() is (less) probably not save against power loses.

    • load

      public void load(int percentage)
      Load memory mapped files into physical memory.

    • close

      public void close()
      Description copied from interface: DataAccess
      This method makes sure that the underlying used resources are released. WARNING: it does NOT flush on close!
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface DataAccess
      Overrides:
      close in class AbstractDataAccess

    • setInt

      public void setInt(long bytePos, int value)
      Description copied from interface: DataAccess
      Set 4 bytes at position 'bytePos' to the specified value

    • getInt

      public int getInt(long bytePos)
      Description copied from interface: DataAccess
      Get 4 bytes from position 'bytePos'

    • setShort

      public void setShort(long bytePos, short value)
      Description copied from interface: DataAccess
      Set 2 bytes at position 'index' to the specified value

    • getShort

      public short getShort(long bytePos)
      Description copied from interface: DataAccess
      Get 2 bytes from position 'index'

    • setBytes

      public void setBytes(long bytePos, byte[] values, int length)
      Description copied from interface: DataAccess
      Set bytes from position 'index' to the specified values

    • getBytes

      public void getBytes(long bytePos, byte[] values, int length)
      Description copied from interface: DataAccess
      Get bytes from position 'index'
      values - acts as output

    • setByte

      public void setByte(long bytePos, byte value)

    • getByte

      public byte getByte(long bytePos)

    • getCapacity

      public long getCapacity()
      Returns:
      the allocated storage size in bytes

    • getSegments

      public int getSegments()
      Returns:
      the number of segments.

    • getType

      public DAType getType()
      Returns:
      the data access type of this object.