Package org.apache.hadoop.io.nativeio

Class SharedFileDescriptorFactory

java.lang.Object

org.apache.hadoop.io.nativeio.SharedFileDescriptorFactory

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

A factory for creating shared file descriptors inside a given directory. Typically, the directory will be /dev/shm or /tmp. We will hand out file descriptors that correspond to unlinked files residing in that directory. These file descriptors are suitable for sharing across multiple processes and are both readable and writable. Because we unlink the temporary files right after creating them, a JVM crash usually does not leave behind any temporary files in the directory. However, it may happen that we crash right after creating the file and before unlinking it. In the constructor, we attempt to clean up after any such remnants by trying to unlink any temporary files created by previous SharedFileDescriptorFactory instances that also used our prefix.

Field Summary

Fields

Modifier and Type	Field	Description
static org.slf4j.Logger	LOG

Method Summary

Modifier and Type	Method	Description
static SharedFileDescriptorFactory	create(java.lang.String prefix, java.lang.String[] paths)	Create a new SharedFileDescriptorFactory.
java.io.FileInputStream	createDescriptor(java.lang.String info, int length)	Create a shared file descriptor which will be both readable and writable.
static java.lang.String	getLoadingFailureReason()
java.lang.String	getPath()

Methods inherited from class java.lang.Object

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

Field Detail

LOG

public static final org.slf4j.Logger LOG

Method Detail

getLoadingFailureReason

public static java.lang.String getLoadingFailureReason()

create

public static SharedFileDescriptorFactory create(java.lang.String prefix,
                                                 java.lang.String[] paths)
                                          throws java.io.IOException

Create a new SharedFileDescriptorFactory.

Parameters:

prefix - The prefix to prepend to all the file names created by this factory.

paths - An array of paths to use. We will try each path in succession, and return a factory using the first usable path.

Returns:

The factory.

Throws:

java.io.IOException - If a factory could not be created for any reason.

getPath

public java.lang.String getPath()

createDescriptor

public java.io.FileInputStream createDescriptor(java.lang.String info,
                                                int length)
                                         throws java.io.IOException

Create a shared file descriptor which will be both readable and writable.

Parameters:

info - Information to include in the path of the generated descriptor.

length - The starting file length.

Returns:

The file descriptor, wrapped in a FileInputStream.

Throws:

java.io.IOException - If there was an I/O or configuration error creating the descriptor.