org.eclipse.jgit.storage.file
Class FileSnapshot

java.lang.Object
  org.eclipse.jgit.storage.file.FileSnapshot

public class FileSnapshot
extends Object

Caches when a file was last read, making it possible to detect future edits.

This object tracks the last modified time of a file. Later during an invocation of isModified(File) the object will return true if the file may have been modified and should be re-read from disk.

A snapshot does not "live update" when the underlying filesystem changes. Callers must poll for updates by periodically invoking isModified(File).

To work around the "racy git" problem (where a file may be modified multiple times within the granularity of the filesystem modification clock) this class may return true from isModified(File) if the last modification time of the file is less than 3 seconds ago.

Field Summary

static FileSnapshot	DIRTY A FileSnapshot that is considered to always be modified.
static FileSnapshot	MISSING_FILE A FileSnapshot that is clean if the file does not exist.

Method Summary

boolean	equals(FileSnapshot other) Compare two snapshots to see if they cache the same information.
boolean	equals(Object other)
int	hashCode()
boolean	isModified(File path) Check if the path may have been modified since the snapshot was saved.
long	lastModified()
static FileSnapshot	save(File path) Record a snapshot for a specific file path.
static FileSnapshot	save(long modified) Record a snapshot for a file for which the last modification time is already known.
void	setClean(FileSnapshot other) Update this snapshot when the content hasn't changed.

Methods inherited from class java.lang.Object

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

Field Detail

DIRTY

public static final FileSnapshot DIRTY

A FileSnapshot that is considered to always be modified.

This instance is useful for application code that wants to lazily read a file, but only after isModified(File) gets invoked. The returned snapshot contains only invalid status information.

MISSING_FILE

public static final FileSnapshot MISSING_FILE

A FileSnapshot that is clean if the file does not exist.

This instance is useful if the application wants to consider a missing file to be clean. isModified(File) will return false if the file path does not exist.

Method Detail

save

public static FileSnapshot save(File path)

Record a snapshot for a specific file path.

This method should be invoked before the file is accessed.

Parameters:

path - the path to later remember. The path's current status information is saved.

Returns:

the snapshot.

save

public static FileSnapshot save(long modified)

Record a snapshot for a file for which the last modification time is already known.

This method should be invoked before the file is accessed.

Parameters:

modified - the last modification time of the file

Returns:

the snapshot.

lastModified

public long lastModified()

Returns:

time of last snapshot update

isModified

public boolean isModified(File path)

Check if the path may have been modified since the snapshot was saved.

Parameters:

path - the path the snapshot describes.

Returns:

true if the path needs to be read again.

setClean

public void setClean(FileSnapshot other)

Update this snapshot when the content hasn't changed.

If the caller gets true from isModified(File), re-reads the content, discovers the content is identical, and equals(FileSnapshot) is true, it can use setClean(FileSnapshot) to make a future isModified(File) return false. The logic goes something like this:

 if (snapshot.isModified(path)) {
  FileSnapshot other = FileSnapshot.save(path);
  Content newContent = ...;
  if (oldContent.equals(newContent) && snapshot.equals(other))
      snapshot.setClean(other);
 }
 

Parameters:

other - the other snapshot.

equals

public boolean equals(FileSnapshot other)

Compare two snapshots to see if they cache the same information.

Parameters:

other - the other snapshot.

Returns:

true if the two snapshots share the same information.

equals

public boolean equals(Object other)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object