com.sun.jna.platform.unix

Class LibCUtil

java.lang.Object

com.sun.jna.platform.unix.LibCUtil

public class LibCUtil
extends java.lang.Object

Utility class supporting variable-width types in the C Library. Portable code should avoid using off_t because it is dependent upon features selected at compile-time. This class provides helper methods that safely avoid these types by using 64-bit mappings when available.

Method Summary

Modifier and Type	Method and Description
static int	ftruncate(int fd, long length) Causes the regular file referenced by fd to be truncated to a size of precisely length bytes.
static Pointer	mmap(Pointer addr, long length, int prot, int flags, int fd, long offset) Creates a new mapping in the virtual address space of the calling process.
static void	require32Bit(long val, java.lang.String value) Test that a value is 32-bit, throwing a custom exception otherwise

Methods inherited from class java.lang.Object

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

Method Detail

mmap

public static Pointer mmap(Pointer addr,
                           long length,
                           int prot,
                           int flags,
                           int fd,
                           long offset)

Creates a new mapping in the virtual address space of the calling process.

Parameters:

addr - The starting address for the new mapping.

If addr is NULL, then the kernel chooses the (page-aligned) address at which to create the mapping; this is the most portable method of creating a new mapping. If addr is not NULL, then the kernel takes it as a hint about where to place the mapping; on Linux, the kernel will pick a nearby page boundary (but always above or equal to the value specified by /proc/sys/vm/mmap_min_addr) and attempt to create the mapping there. If another mapping already exists there, the kernel picks a new address that may or may not depend on the hint. The address of the new mapping is returned as the result of the call.

length - Specifies the length of the mapping (which must be greater than 0).

prot - describes the desired memory protection of the mapping (and must not conflict with the open mode of the file). It is either PROT_NONE or the bitwise OR of one or more of PROT_READ, PROT_WRITE, or PROT_EXEC.

flags - determines whether updates to the mapping are visible to other processes mapping the same region, and whether updates are carried through to the underlying file. This behavior is determined by including exactly one of MAP_SHARED, MAP_SHARED_VALIDATE, or MAP_PRIVATE. In addition, 0 or more additional flags can be ORed in flags.

fd - The file descriptor for the object to be mapped. After the mmap() call has returned, the file descriptor can be closed immediately without invalidating the mapping.

offset - The contents of a file mapping (as opposed to an anonymous mapping), are initialized using length bytes starting at offset offset in the file (or other object) referred to by the file descriptor, fd. offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

Returns:

On success, returns a pointer to the mapped area. On error, the value MAP_FAILED (that is, (void *) -1) is returned, and errno is set to indicate the cause of the error.

ftruncate

public static int ftruncate(int fd,
                            long length)

Causes the regular file referenced by fd to be truncated to a size of precisely length bytes.

If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is extended, and the extended part reads as null bytes ('\0').

The file must be open for writing

Parameters:

fd - a file descriptor

length - the number of bytes to truncate or extend the file to

Returns:

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

require32Bit

public static void require32Bit(long val,
                                java.lang.String value)

Test that a value is 32-bit, throwing a custom exception otherwise

Parameters:

val - The value to test

value - The name of the value, to be inserted in the exception message if not 32-bit

Throws:

java.lang.IllegalArgumentException - if val is not 32-bit