Package com.github.marschall.nativebytebuffers

Class Mman

java.lang.Object

com.github.marschall.nativebytebuffers.Mman

public final class Mman
extends Object

Provides access to memory management using sys/mman.h.

Method Summary

Modifier and Type	Method	Description
static long	getpagesize()	Returns the number of bytes in a memory page, where "page" is a fixed-length block, the unit for memory allocation and file mapping performed by mmap(int, int).
static int	memfd_create(String name, int flags)	Calls memfd_create() to create an anonymous file and returns a file descriptor that refers to it.
static ByteBuffer	mmap(int length)	Calls mmap() to create an anonymous shared virtual memory region and creates a ByteBuffer around it.
static ByteBuffer	mmap(int length, int flags)	Calls mmap() to create a virtual memory region and creates a ByteBuffer around it.
static ByteBuffer	mmap(int length, int flags, int fd)
static void	munmap(ByteBuffer buffer)	Calls munmap() on the contents of the given ByteBuffer.

Methods inherited from class java.lang.Object

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

Method Details

mmap

public static ByteBuffer mmap(int length)

Calls mmap() to create an anonymous shared virtual memory region and creates a ByteBuffer around it.

Protection will be PROT_READ | PROT_WRITE.

Parameters:

length - the length of the mapping, must be greater than 0

Returns:

a new ByteBuffer around the newly mmap()-ed area, never null, must be released with munmap(ByteBuffer)

Throws:

IllegalArgumentException - if length is not positive

AllocationFailedException - if mmap() fails

See Also:

• mmap(int, int)
• munmap(ByteBuffer)
• mmap(2)

mmap

public static ByteBuffer mmap(int length,
 int flags)

Calls mmap() to create a virtual memory region and creates a ByteBuffer around it.

Protection will be PROT_READ | PROT_WRITE.

Parameters:

length - the length of the mapping, must be greater than 0

flags - ORed arguments from MmapFlags that control various aspects of the mapping

Returns:

a new ByteBuffer around the newly mmap()-ed area, never null, must be released with munmap(ByteBuffer)

Throws:

IllegalArgumentException - if length is not positive

AllocationFailedException - if mmap() fails

See Also:

• munmap(ByteBuffer)
• mmap(2)

mmap

public static ByteBuffer mmap(int length,
 int flags,
 int fd)

munmap

public static void munmap(ByteBuffer buffer)

Calls munmap() on the contents of the given ByteBuffer.

This method may crash the JVM the buffer passed has not been created by mmap(int, int), mmap(int) or has already been passed to this method.

Parameters:

buffer - the buffer to free, not null, must have been created with mmap(int, int) or mmap(int), must not be accessed afterwards, must not be passed to this method again

Throws:

NullPointerException - if buffer is null

IllegalArgumentException - if buffer is not a direct buffer

ReleaseFailedException - if unmapping fails

See Also:

• munmap(ByteBuffer)
• mmap(2)

memfd_create

public static int memfd_create(String name,
 int flags)
                        throws IOException

Calls memfd_create() to create an anonymous file and returns a file descriptor that refers to it.

Parameters:

name - the name supplied in name is used as a filename and will be displayed as the target of the corresponding symbolic link in the directory /proc/self/fd/. The displayed name is always prefixed with memfd: and serves only for debugging purposes. Names do not affect the behavior of the file descriptor, and as such multiple files can have the same name without any side effects. Must not be longer than 249 in the native encoding

flags - bitwise ORed in flags to change the behavior of memfd_create()

Returns:

new file descriptor that can be used to refer to the file. This file descriptor is opened for both reading and writing.

Throws:

IOException - if memfd_create() fails

See Also:

• MemfdCreateFlags
• memfd_create(2)

getpagesize

public static long getpagesize()

Returns the number of bytes in a memory page, where "page" is a fixed-length block, the unit for memory allocation and file mapping performed by mmap(int, int).

Returns:

the page size, long because in theory we could have pages larger than 2 GiB

See Also:

• getpagesize(2)