Class FileSnapshot
- java.lang.Object
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- org.eclipse.jgit.internal.storage.file.FileSnapshot
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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.
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Field Summary
Fields Modifier and Type Field Description 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.static long
UNKNOWN_SIZE
An unknown file size.
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Constructor Summary
Constructors Modifier Constructor Description protected
FileSnapshot(File file)
Record a snapshot for a specific file path.protected
FileSnapshot(File file, boolean useConfig)
Record a snapshot for a specific file path.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method Description boolean
equals(Object obj)
boolean
equals(FileSnapshot other)
Compare two snapshots to see if they cache the same information.int
hashCode()
boolean
isModified(File path)
Check if the path may have been modified since the snapshot was saved.long
lastDelta()
long
lastModified()
Deprecated.uselastModifiedInstant()
insteadInstant
lastModifiedInstant()
Get time of last snapshot updatelong
lastRacyThreshold()
static FileSnapshot
save(long modified)
Deprecated.usesave(Instant)
instead.static FileSnapshot
save(File path)
Record a snapshot for a specific file path.static FileSnapshot
save(Instant modified)
Record a snapshot for a file for which the last modification time is already known.static FileSnapshot
saveNoConfig(File path)
Record a snapshot for a specific file path without using config file to get filesystem timestamp resolution.void
setClean(FileSnapshot other)
Update this snapshot when the content hasn't changed.long
size()
String
toString()
void
waitUntilNotRacy()
Wait until this snapshot's file can't be racy anymore
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Field Detail
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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
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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.
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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.
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Constructor Detail
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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.
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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
- iftrue
read filesystem time resolution from configuration file otherwise use fallback resolution
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Method Detail
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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.
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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.
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save
@Deprecated public static FileSnapshot save(long modified)
Deprecated.usesave(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.
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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.
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lastModified
@Deprecated public long lastModified()
Deprecated.uselastModifiedInstant()
insteadGet time of last snapshot update- Returns:
- time of last snapshot update
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lastModifiedInstant
public Instant lastModifiedInstant()
Get time of last snapshot update- Returns:
- time of last snapshot update
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size
public long size()
- Returns:
- file size in bytes of last snapshot update
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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.
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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, andequals(FileSnapshot)
is true, it can usesetClean(FileSnapshot)
to make a futureisModified(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.
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waitUntilNotRacy
public void waitUntilNotRacy() throws InterruptedException
Wait until this snapshot's file can't be racy anymore- Throws:
InterruptedException
- if sleep was interrupted
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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.
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lastDelta
public long lastDelta()
- Returns:
- the delta in nanoseconds between lastModified and lastRead during last racy check
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lastRacyThreshold
public long lastRacyThreshold()
- Returns:
- the racyLimitNanos threshold in nanoseconds during last racy check
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