com.facebook.buck.util.filesystem

Class FileSystemMap<T>

java.lang.Object

com.facebook.buck.util.filesystem.FileSystemMap<T>

Type Parameters:

T - The type to associate with a specific path.

public class FileSystemMap<T>
extends Object

This class implements a map for a filesystem structure relying on a prefix tree. The trie only supports relative paths for now, but an effort can be made in order to let it support absolute paths if needed. Every intermediate or leaf node of the trie is a folder/file which may be associated with a value. It's worth noting that adding a value for path foo/bar/file.txt will add intermediate nodes for foo and foo/bar but not values. The value is associated with the specified path and not with its ancestors. Invalidating one of the leaves or intermediate nodes will cause its parent and its ancestors to be invalidated as well: this operation consists in removing the leaf from its parent children and setting the value of all its ancestors to null. If the removal of the target leaf leaves an empty branch (a stump), that is removed as well in order to keep the prefix tree as slim as possible.

This class is thread safe in its public methods: concurrent calls to the trie will have the exclusiveness in write/remove operations, while allowing parallel reads to the whole data structure: an attempt could be made to make the trie more concurrent by locking branches of the trie instead of the whole object, although that will require some thought around how to grant parallel writes.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	FileSystemMap.ValueLoader<T> Wrapper class that implements a method for loading a value in the leaves of the trie.

Constructor Summary

Constructors

Constructor and Description
FileSystemMap(FileSystemMap.ValueLoader<T> loader, ProjectFilesystem filesystem)

Method Summary

Modifier and Type	Method and Description
com.google.common.collect.ImmutableMap<Path,T>	asMap() Returns a copy of the leaves stored in the trie as a map.
T	get(Path path) Gets the value associated with the given path.
T	getIfPresent(Path path) Gets the value associated with the given path, if found, or `null` otherwise.
void	put(Path path, T value) Puts a path and a value into the map.
void	remove(Path path) Removes the given path.
void	removeAll() Empties the trie leaving only the root node available.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileSystemMap

public FileSystemMap(FileSystemMap.ValueLoader<T> loader,
                     ProjectFilesystem filesystem)

Method Detail

put

public void put(Path path,
                T value)

Puts a path and a value into the map.

Parameters:

path - The path to store.

value - The value to associate to the given path.

remove

public void remove(Path path)

Removes the given path.

Removing a path involves the following:

• all the child nodes of the given path are discarded as well.
• all the paths upstream lose their value.
• each path upstream will be removed if after the removal of the leaf the node is left with no children (that is, it has become a stump).

Parameters:

path - The path specifying the branch to remove.

removeAll

public void removeAll()

Empties the trie leaving only the root node available.

get

public T get(Path path)

Gets the value associated with the given path.

Parameters:

path - The path to fetch.

Returns:

The value associated with the path.

getIfPresent

@Nullable
public T getIfPresent(Path path)

Gets the value associated with the given path, if found, or `null` otherwise.

Parameters:

path - The path to fetch.

Returns:

The value associated with the path.

asMap

public com.google.common.collect.ImmutableMap<Path,T> asMap()

Returns a copy of the leaves stored in the trie as a map. N.B.: this is quite an expensive call to make, so use it wisely.