Package org.eclipse.jgit.internal.storage.file

Class 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 Detail

      • UNKNOWN_SIZE

        public static final long UNKNOWN_SIZE
        An unknown file size. This value is used when a comparison needs to happen purely on the lastUpdate.
        See Also:
        Constant Field Values

      • 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.

    • Constructor Detail

      • FileSnapshot

        protected FileSnapshot​(File file)
        Record a snapshot for a specific file path.

        This method should be invoked before the file is accessed.

        Parameters:
        file - the path to remember meta data for. The path's current status information is saved.

      • FileSnapshot

        protected FileSnapshot​(File file,
                       boolean useConfig)
        Record a snapshot for a specific file path.

        This method should be invoked before the file is accessed.

        Parameters:
        file - the path to remember meta data for. The path's current status information is saved.
        useConfig - if true read filesystem time resolution from configuration file otherwise use fallback resolution

    • 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.

      • saveNoConfig

        public static FileSnapshot saveNoConfig​(File path)
        Record a snapshot for a specific file path without using config file to get filesystem timestamp resolution.

        This method should be invoked before the file is accessed. It is used by FileBasedConfig to avoid endless recursion.

        Parameters:
        path - the path to later remember. The path's current status information is saved.
        Returns:
        the snapshot.

      • save

        @Deprecated
public static FileSnapshot save​(long modified)
        Deprecated.
        use save(Instant) instead.
        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.

        Note that this method cannot rely on measuring file timestamp resolution to avoid racy git issues caused by finite file timestamp resolution since it's unknown in which filesystem the file is located. Hence the worst case fallback for timestamp resolution is used.

        Parameters:
        modified - the last modification time of the file
        Returns:
        the snapshot.

      • save

        public static FileSnapshot save​(Instant 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.

        Note that this method cannot rely on measuring file timestamp resolution to avoid racy git issues caused by finite file timestamp resolution since it's unknown in which filesystem the file is located. Hence the worst case fallback for timestamp resolution is used.

        Parameters:
        modified - the last modification time of the file
        Returns:
        the snapshot.

      • lastModified

        @Deprecated
public long lastModified()
        Deprecated.
        use lastModifiedInstant() instead
        Get time of last snapshot update
        Returns:
        time of last snapshot update

      • lastModifiedInstant

        public Instant lastModifiedInstant()
        Get time of last snapshot update
        Returns:
        time of last snapshot update

      • size

        public long size()
        Returns:
        file size in bytes 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.

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Object

      • lastDelta

        public long lastDelta()
        Returns:
        the delta in nanoseconds between lastModified and lastRead during last racy check

      • lastRacyThreshold

        public long lastRacyThreshold()
        Returns:
        the racyLimitNanos threshold in nanoseconds during last racy check