Class MappedMemory

java.lang.Object

org.newsclub.net.unix.memory.MappedMemory

All Implemented Interfaces:

Closeable, AutoCloseable

public final class MappedMemory
extends Object
implements Closeable

Some mapped memory.

Author:

Christian Kohlschütter

Method Summary

Modifier and Type	Method	Description
static MappedMemory	anonymousCopyOnWriteSegment(Arena arena, long length)	Returns an anonymous copy-on-write (changes are local to the process running this JVM) memory segment of the given length.
static MappedMemory	anonymousReadOnlySegment(Arena arena, long length)	Returns an anonymous read-only memory segment of the given length.
static MappedMemory	anonymousSegment(Arena arena, long length)	Returns an anonymous read/write memory segment of the given length.
void	close()
static long	defaultAllocationSize()	Returns the system's default memory page allocation size for shared memory.
MemorySegment	getMemorySegment()	Returns the MemorySegment backed by this instance.
long	getMinimumSubAllocationSize()	Returns the minimum sub-allocation size.
MappedMemory	mapRegion(long msOffset, long length, FileDescriptor fd, long fdOffset)	Maps some memory to a region of this MappedMemory object.
static MappedMemory	placeholderSegment(Arena arena, long length)	Returns an anonymous memory segment of the given length that acts as a placeholder for later, memory-mapped segments in this area.

Methods inherited from class Object

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

Method Details

getMemorySegment

public MemorySegment getMemorySegment()

Returns the MemorySegment backed by this instance.

Returns:

The MemorySegment.

getMinimumSubAllocationSize

public long getMinimumSubAllocationSize()

Returns the minimum sub-allocation size.

Returns:

The minimum sub-allocation size.

defaultAllocationSize

public static long defaultAllocationSize()

Returns the system's default memory page allocation size for shared memory.

This may be larger than the system's regular page size (e.g., on Windows it's 64k).

Returns:

The page size.

anonymousReadOnlySegment

public static MappedMemory anonymousReadOnlySegment(Arena arena,
 long length)
                                             throws IOException

Returns an anonymous read-only memory segment of the given length.

Parameters:

arena - The arena to associate the MappedMemory instance with.

length - The length of the segment.

Returns:

The MappedMemory segment.

Throws:

IOException - on error.

anonymousSegment

public static MappedMemory anonymousSegment(Arena arena,
 long length)
                                     throws IOException

Returns an anonymous read/write memory segment of the given length.

Parameters:

arena - The arena to associate the MappedMemory instance with.

length - The length of the segment.

Returns:

The MappedMemory segment.

Throws:

IOException - on error.

placeholderSegment

public static MappedMemory placeholderSegment(Arena arena,
 long length)
                                       throws IOException

Returns an anonymous memory segment of the given length that acts as a placeholder for later, memory-mapped segments in this area.

Parameters:

arena - The arena to associate the MappedMemory instance with.

length - The length of the segment.

Returns:

The MappedMemory segment.

Throws:

IOException - on error.

anonymousCopyOnWriteSegment

public static MappedMemory anonymousCopyOnWriteSegment(Arena arena,
 long length)
                                                throws IOException

Returns an anonymous copy-on-write (changes are local to the process running this JVM) memory segment of the given length.

Parameters:

arena - The arena to associate the MappedMemory instance with.

length - The length of the segment.

Returns:

The MappedMemory segment.

Throws:

IOException - on error.

mapRegion

public MappedMemory mapRegion(long msOffset,
 long length,
 FileDescriptor fd,
 long fdOffset)
                       throws IOException

Maps some memory to a region of this MappedMemory object. This may fail to work on Windows, unless placeholderSegment(Arena, long) was used to create this MappedMemory instance.

Parameters:

msOffset - The target offset in this object.

length - The number of bytes to map.

fd - The file descriptor to map from.

fdOffset - The file descriptor-specific content offset

Returns:

A new MappedMemory object, whose MemorySegment is a subrange of this object's MemorySegment.

Throws:

IOException - on error.

See Also:

• placeholderSegment(Arena, long)

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Throws:

IOException