Package org.apache.hadoop.io.nativeio

Class NativeIO

java.lang.Object

org.apache.hadoop.io.nativeio.NativeIO

@Private
@Unstable
public class NativeIO
extends java.lang.Object

JNI wrappers for various native IO-related calls not available in Java. These functions should generally be used alongside a fallback to another more portable mechanism.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	NativeIO.POSIX
static class	NativeIO.Windows

Constructor Summary

Constructors

Constructor	Description
NativeIO()

Method Summary

Modifier and Type	Method	Description
static void	copyFileUnbuffered(java.io.File src, java.io.File dst)	Unbuffered file copy from src to dst without tainting OS buffer cache In POSIX platform: It uses FileChannel#transferTo() which internally attempts unbuffered IO on OS with native sendfile64() support and falls back to buffered IO otherwise.
static java.io.FileOutputStream	getCreateForWriteFileOutputStream(java.io.File f, int permissions)
static java.lang.String	getOwner(java.io.FileDescriptor fd)
static java.io.FileDescriptor	getShareDeleteFileDescriptor(java.io.File f, long seekOffset)	Create a FileDescriptor that shares delete permission on the file opened at a given offset, i.e.
static boolean	isAvailable()
static void	link(java.io.File src, java.io.File dst)	Deprecated.
static void	renameTo(java.io.File src, java.io.File dst)	A version of renameTo that throws a descriptive exception when it fails.

Methods inherited from class java.lang.Object

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

Constructor Detail

NativeIO

public NativeIO()

Method Detail

isAvailable

public static boolean isAvailable()

Returns:

Return true if the JNI-based native IO extensions are available.

getOwner

public static java.lang.String getOwner(java.io.FileDescriptor fd)
                                 throws java.io.IOException

Throws:

java.io.IOException

getShareDeleteFileDescriptor

public static java.io.FileDescriptor getShareDeleteFileDescriptor(java.io.File f,
                                                                  long seekOffset)
                                                           throws java.io.IOException

Create a FileDescriptor that shares delete permission on the file opened at a given offset, i.e. other process can delete the file the FileDescriptor is reading. Only Windows implementation uses the native interface.

Parameters:

f - input f.

seekOffset - input seekOffset.

Returns:

FileDescriptor.

Throws:

java.io.IOException - raised on errors performing I/O.

getCreateForWriteFileOutputStream

public static java.io.FileOutputStream getCreateForWriteFileOutputStream(java.io.File f,
                                                                         int permissions)
                                                                  throws java.io.IOException

Parameters:

f - the file that we want to create

permissions - we want to have on the file (if security is enabled)

Returns:

Create the specified File for write access, ensuring that it does not exist.

Throws:

SecureIOUtils.AlreadyExistsException - if the file already exists

java.io.IOException - if any other error occurred

renameTo

public static void renameTo(java.io.File src,
                            java.io.File dst)
                     throws java.io.IOException

A version of renameTo that throws a descriptive exception when it fails.

Parameters:

src - The source path

dst - The destination path

Throws:

NativeIOException - On failure.

java.io.IOException

link

@Deprecated
public static void link(java.io.File src,
                        java.io.File dst)
                 throws java.io.IOException

Deprecated.

Creates a hardlink "dst" that points to "src". This is deprecated since JDK7 NIO can create hardlinks via the Files API.

Parameters:

src - source file

dst - hardlink location

Throws:

java.io.IOException - raised on errors performing I/O.

copyFileUnbuffered

public static void copyFileUnbuffered(java.io.File src,
                                      java.io.File dst)
                               throws java.io.IOException

Unbuffered file copy from src to dst without tainting OS buffer cache In POSIX platform: It uses FileChannel#transferTo() which internally attempts unbuffered IO on OS with native sendfile64() support and falls back to buffered IO otherwise. It minimizes the number of FileChannel#transferTo call by passing the the src file size directly instead of a smaller size as the 3rd parameter. This saves the number of sendfile64() system call when native sendfile64() is supported. In the two fall back cases where sendfile is not supported, FileChannle#transferTo already has its own batching of size 8 MB and 8 KB, respectively. In Windows Platform: It uses its own native wrapper of CopyFileEx with COPY_FILE_NO_BUFFERING flag, which is supported on Windows Server 2008 and above. Ideally, we should use FileChannel#transferTo() across both POSIX and Windows platform. Unfortunately, the wrapper(Java_sun_nio_ch_FileChannelImpl_transferTo0) used by FileChannel#transferTo for unbuffered IO is not implemented on Windows. Based on OpenJDK 6/7/8 source code, Java_sun_nio_ch_FileChannelImpl_transferTo0 on Windows simply returns IOS_UNSUPPORTED. Note: This simple native wrapper does minimal parameter checking before copy and consistency check (e.g., size) after copy. It is recommended to use wrapper function like the Storage#nativeCopyFileUnbuffered() function in hadoop-hdfs with pre/post copy checks.

Parameters:

src - The source path

dst - The destination path

Throws:

java.io.IOException - raised on errors performing I/O.