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

Field Summary

Fields inherited from class com.graphhopper.storage.AbstractDataAccess

bitUtil, byteOrder, closed, EMPTY, header, HEADER_OFFSET, indexDivisor, name, SEGMENT_SIZE_MIN, segmentSizeInBytes, segmentSizePower

Method Summary

Modifier and Type	Method	Description
static void	cleanMappedByteBuffer(ByteBuffer buffer)
void	close()	This method makes sure that the underlying used resources are released.
MMapDataAccess	create(long bytes)	The first time you use a DataAccess object after configuring it you need to call this method.
boolean	ensureCapacity(long bytes)	Ensures that the capacity of this object is at least the specified bytes.
void	flush()	This method makes sure that the underlying data is written to the storage.
byte	getByte(long bytePos)
void	getBytes(long bytePos, byte[] values, int length)	Get bytes from position 'index'
long	getCapacity()
int	getInt(long bytePos)	Get 4 bytes from position 'bytePos'
int	getSegments()
short	getShort(long bytePos)	Get 2 bytes from position 'index'
DAType	getType()
void	load(int percentage)	Load memory mapped files into physical memory.
boolean	loadExisting()
void	setByte(long bytePos, byte value)
void	setBytes(long bytePos, byte[] values, int length)	Set bytes from position 'index' to the specified values
void	setInt(long bytePos, int value)	Set 4 bytes at position 'bytePos' to the specified value
void	setShort(long bytePos, short value)	Set 2 bytes at position 'index' to the specified value

Methods inherited from class com.graphhopper.storage.AbstractDataAccess

copyHeader, getFullName, getHeader, getName, getSegmentSize, isClosed, isIntBased, isStoring, readHeader, setHeader, toString, writeHeader

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

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:

• DataAccess.create(long)

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.