org.apache.hadoop.io

类 ReadaheadPool

java.lang.Object

org.apache.hadoop.io.ReadaheadPool

@InterfaceAudience.Private
@InterfaceStability.Evolving
public class ReadaheadPool
extends Object

Manages a pool of threads which can issue readahead requests on file descriptors.

嵌套类概要

嵌套类

限定符和类型	类和说明
static interface	ReadaheadPool.ReadaheadRequest An outstanding readahead request that has been submitted to the pool.

方法概要

方法

限定符和类型	方法和说明
static ReadaheadPool	getInstance() Return the singleton instance for the current process.
ReadaheadPool.ReadaheadRequest	readaheadStream(String identifier, FileDescriptor fd, long curPos, long readaheadLength, long maxOffsetToRead, ReadaheadPool.ReadaheadRequest lastReadahead) Issue a request to readahead on the given file descriptor.
ReadaheadPool.ReadaheadRequest	submitReadahead(String identifier, FileDescriptor fd, long off, long len) Submit a request to readahead on the given file descriptor.

从类继承的方法 java.lang.Object

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

方法详细资料

getInstance

public static ReadaheadPool getInstance()

Return the singleton instance for the current process.

readaheadStream

public ReadaheadPool.ReadaheadRequest readaheadStream(String identifier,
                                             FileDescriptor fd,
                                             long curPos,
                                             long readaheadLength,
                                             long maxOffsetToRead,
                                             ReadaheadPool.ReadaheadRequest lastReadahead)

Issue a request to readahead on the given file descriptor.

参数:

identifier - a textual identifier that will be used in error messages (e.g. the file name)

fd - the file descriptor to read ahead

curPos - the current offset at which reads are being issued

readaheadLength - the configured length to read ahead

maxOffsetToRead - the maximum offset that will be readahead (useful if, for example, only some segment of the file is requested by the user). Pass Long.MAX_VALUE to allow readahead to the end of the file.

lastReadahead - the result returned by the previous invocation of this function on this file descriptor, or null if this is the first call

返回:

an object representing this outstanding request, or null if no readahead was performed

submitReadahead

public ReadaheadPool.ReadaheadRequest submitReadahead(String identifier,
                                             FileDescriptor fd,
                                             long off,
                                             long len)

Submit a request to readahead on the given file descriptor.

参数:

identifier - a textual identifier used in error messages, etc.

fd - the file descriptor to readahead

off - the offset at which to start the readahead

len - the number of bytes to read

返回:

an object representing this pending request