Package org.apache.hadoop.hbase.io

Class FileChangeWatcher

java.lang.Object

org.apache.hadoop.hbase.io.FileChangeWatcher

@Private
public final class FileChangeWatcher
extends Object

Instances of this class can be used to watch a directory for file changes. When a file is added to, deleted from, or is modified in the given directory, the callback provided by the user will be called from a background thread. Some things to keep in mind:

• The callback should be thread-safe.
• Changes that happen around the time the thread is started may be missed.
• There is a delay between a file changing and the callback firing.
• The watch is not recursive - changes to subdirectories will not trigger a callback.

This file has been copied from the Apache ZooKeeper project.

See Also:

• Base revision

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	FileChangeWatcher.State
private class	FileChangeWatcher.WatcherThread	Inner class that implements the watcher thread logic.

Field Summary

Fields

Modifier and Type	Field	Description
private static final org.slf4j.Logger	LOG
private FileChangeWatcher.State	state
private final FileChangeWatcher.WatcherThread	watcherThread

Constructor Summary

Constructors

Constructor	Description
FileChangeWatcher(Path dirPath, String threadNameSuffix, Consumer<WatchEvent<?>> callback)	Creates a watcher that watches dirPath and invokes callback on changes.

Method Summary

Modifier and Type	Method	Description
private boolean	compareAndSetState(FileChangeWatcher.State[] expectedStates, FileChangeWatcher.State update)	Atomically sets the state to update if and only if the state is currently one of expectedStates.
private boolean	compareAndSetState(FileChangeWatcher.State expected, FileChangeWatcher.State update)	Atomically sets the state to update if and only if the state is currently expected.
FileChangeWatcher.State	getState()	Returns the current FileChangeWatcher.State.
(package private) String	getWatcherThreadName()
private static void	handleException(Thread thread, Throwable e)
private void	setState(FileChangeWatcher.State newState)	Sets the state to newState.
void	start()	Tells the background thread to start.
void	stop()	Tells the background thread to stop.
(package private) void	waitForState(FileChangeWatcher.State desiredState)	Blocks until the current state becomes desiredState.

Methods inherited from class java.lang.Object

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

Field Details

LOG

private static final org.slf4j.Logger LOG

watcherThread

private final FileChangeWatcher.WatcherThread watcherThread

state

private FileChangeWatcher.State state

Constructor Details

FileChangeWatcher

public FileChangeWatcher(Path dirPath,
 String threadNameSuffix,
 Consumer<WatchEvent<?>> callback)
                  throws IOException

Creates a watcher that watches dirPath and invokes callback on changes.

Parameters:

dirPath - the directory to watch.

callback - the callback to invoke with events. event.kind() will return the type of event, and event.context() will return the filename relative to dirPath.

Throws:

IOException - if there is an error creating the WatchService.

Method Details

getState

public FileChangeWatcher.State getState()

Returns the current FileChangeWatcher.State.

Returns:

the current state.

waitForState

void waitForState(FileChangeWatcher.State desiredState)
           throws InterruptedException

Blocks until the current state becomes desiredState. Currently only used by tests, thus package-private.

Parameters:

desiredState - the desired state.

Throws:

InterruptedException - if the current thread gets interrupted.

setState

private void setState(FileChangeWatcher.State newState)

Sets the state to newState.

Parameters:

newState - the new state.

compareAndSetState

private boolean compareAndSetState(FileChangeWatcher.State expected,
 FileChangeWatcher.State update)

Atomically sets the state to update if and only if the state is currently expected.

Parameters:

expected - the expected state.

update - the new state.

Returns:

true if the update succeeds, or false if the current state does not equal expected.

compareAndSetState

private boolean compareAndSetState(FileChangeWatcher.State[] expectedStates,
 FileChangeWatcher.State update)

Atomically sets the state to update if and only if the state is currently one of expectedStates.

Parameters:

expectedStates - the expected states.

update - the new state.

Returns:

true if the update succeeds, or false if the current state does not equal any of the expectedStates.

start

public void start()

Tells the background thread to start. Does not wait for it to be running. Calling this method more than once has no effect.

stop

public void stop()

Tells the background thread to stop. Does not wait for it to exit.

getWatcherThreadName

String getWatcherThreadName()

handleException

private static void handleException(Thread thread,
 Throwable e)