org.apache.flink.runtime.io.disk.iomanager

Class BlockChannelAccess<R extends org.apache.flink.runtime.io.disk.iomanager.IORequest,C extends Collection<MemorySegment>>

java.lang.Object

org.apache.flink.runtime.io.disk.iomanager.ChannelAccess<MemorySegment,R>

org.apache.flink.runtime.io.disk.iomanager.BlockChannelAccess<R,C>

Type Parameters:

R - The type of request (e.g. ReadRequest or WriteRequest issued by this access to the I/O threads.

C - The type of collection used to collect the segments from completed requests. Those segments are for example for write requests the written and reusable segments, and for read requests the now full and usable segments. The collection type may for example be a synchronized queue or an unsynchronized list.

Direct Known Subclasses:

BlockChannelReader, BlockChannelWriter, BulkBlockChannelReader

public abstract class BlockChannelAccess<R extends org.apache.flink.runtime.io.disk.iomanager.IORequest,C extends Collection<MemorySegment>>
extends ChannelAccess<MemorySegment,R>

A base class for readers and writers that accept read or write requests for whole blocks. The request is delegated to an asynchronous I/O thread. After completion of the I/O request, the memory segment of the block is added to a collection to be returned.

The asynchrony of the access makes it possible to implement read-ahead or write-behind types of I/O accesses.

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	closed Flag marking this channel as closed;
protected Object	closeLock The lock that is used during closing to synchronize the thread that waits for all requests to be handled with the asynchronous I/O thread.
protected AtomicInteger	requestsNotReturned An atomic integer that counts the number of buffers we still wait for to return.
protected C	returnBuffers The collection gathering the processed buffers that are ready to be (re)used.

Fields inherited from class org.apache.flink.runtime.io.disk.iomanager.ChannelAccess

exception, fileChannel, id, requestQueue

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	BlockChannelAccess(Channel.ID channelID, RequestQueue<R> requestQueue, C returnQueue, boolean writeEnabled) Creates a new channel access to the path indicated by the given ID.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes the reader and waits until all pending asynchronous requests are handled.
void	closeAndDelete() This method waits for all pending asynchronous requests to return.
C	getReturnQueue() Gets the queue (or list) to which the asynchronous reader adds its elements.
boolean	isClosed() Checks, whether this channel has been closed;
protected void	returnBuffer(MemorySegment buffer) This method is invoked by the asynchronous I/O thread to return a buffer after the I/O request completed.

Methods inherited from class org.apache.flink.runtime.io.disk.iomanager.ChannelAccess

checkErroneous, deleteChannel, getChannelID

Methods inherited from class java.lang.Object

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

Field Detail

closeLock

protected final Object closeLock

The lock that is used during closing to synchronize the thread that waits for all requests to be handled with the asynchronous I/O thread.

requestsNotReturned

protected final AtomicInteger requestsNotReturned

An atomic integer that counts the number of buffers we still wait for to return.

returnBuffers

protected final C extends Collection<MemorySegment> returnBuffers

The collection gathering the processed buffers that are ready to be (re)used.

closed

protected volatile boolean closed

Flag marking this channel as closed;

Constructor Detail

BlockChannelAccess

protected BlockChannelAccess(Channel.ID channelID,
                  RequestQueue<R> requestQueue,
                  C returnQueue,
                  boolean writeEnabled)
                      throws IOException

Creates a new channel access to the path indicated by the given ID. The channel accepts buffers to be read/written and hands them to the asynchronous I/O thread. After being processed, the buffers are returned by adding the to the given queue.

Parameters:

channelID - The id describing the path of the file that the channel accessed.

requestQueue - The queue that this channel hands its IO requests to.

returnQueue - The queue to which the segments are added after their buffer was written.

writeEnabled - Flag describing whether the channel should be opened in read/write mode, rather than in read-only mode.

Throws:

IOException - Thrown, if the channel could no be opened.

Method Detail

getReturnQueue

public C getReturnQueue()

Gets the queue (or list) to which the asynchronous reader adds its elements.

Returns:

The queue (or list) to which the asynchronous reader adds its elements.

isClosed

public boolean isClosed()

Description copied from class: ChannelAccess

Checks, whether this channel has been closed;

Specified by:

isClosed in class ChannelAccess<MemorySegment,R extends org.apache.flink.runtime.io.disk.iomanager.IORequest>

Returns:

True, if the channel has been closed, false otherwise.

close

public void close()
           throws IOException

Closes the reader and waits until all pending asynchronous requests are handled. Even if an exception interrupts the closing, the underlying FileChannel is closed.

Throws:

IOException - Thrown, if an I/O exception occurred while waiting for the buffers, or if the closing was interrupted.

closeAndDelete

public void closeAndDelete()
                    throws IOException

This method waits for all pending asynchronous requests to return. When the last request has returned, the channel is closed and deleted. Even if an exception interrupts the closing, such that not all request are handled, the underlying FileChannel is closed and deleted.

Throws:

IOException - Thrown, if an I/O exception occurred while waiting for the buffers, or if the closing was interrupted.

returnBuffer

protected void returnBuffer(MemorySegment buffer)

Description copied from class: ChannelAccess

This method is invoked by the asynchronous I/O thread to return a buffer after the I/O request completed.

Specified by:

returnBuffer in class ChannelAccess<MemorySegment,R extends org.apache.flink.runtime.io.disk.iomanager.IORequest>

Parameters:

buffer - The buffer to be returned.