org.eclipse.jgit.storage.dfs
Class DfsReader

java.lang.Object
  extended by org.eclipse.jgit.lib.ObjectReader
      extended by org.eclipse.jgit.storage.dfs.DfsReader
All Implemented Interfaces:
ObjectReuseAsIs

public final class DfsReader
extends ObjectReader
implements ObjectReuseAsIs

Reader to access repository content through.

See the base ObjectReader documentation for details. Notably, a reader is not thread safe.


Field Summary
 
Fields inherited from class org.eclipse.jgit.lib.ObjectReader
OBJ_ANY
 
Method Summary
 void copyObjectAsIs(PackOutputStream out, ObjectToPack otp, boolean validate)
          Output a previously selected representation.
 void copyPackAsIs(PackOutputStream out, CachedPack pack, boolean validate)
          Append an entire pack's contents onto the output stream.
 Collection<CachedPack> getCachedPacks()
          Obtain the available cached packs.
 long getObjectSize(AnyObjectId objectId, int typeHint)
          Get only the size of an object.
<T extends ObjectId>
AsyncObjectSizeQueue<T>
getObjectSize(Iterable<T> objectIds, boolean reportMissing)
          Asynchronous object size lookup.
 Set<ObjectId> getShallowCommits()
          Returns IDs for those commits which should be considered as shallow.
 boolean has(AnyObjectId objectId)
          Does the requested object exist in this database?
 org.eclipse.jgit.storage.dfs.DfsObjectToPack newObjectToPack(RevObject obj)
          Allocate a new PackWriter state structure for an object.
 ObjectReader newReader()
          Construct a new reader from the same data.
 ObjectLoader open(AnyObjectId objectId, int typeHint)
          Open an object from this database.
<T extends ObjectId>
AsyncObjectLoaderQueue<T>
open(Iterable<T> objectIds, boolean reportMissing)
          Asynchronous object opening.
 void release()
          Release the current window cursor.
 Collection<ObjectId> resolve(AbbreviatedObjectId id)
          Resolve an abbreviated ObjectId to its full form.
 void selectObjectRepresentation(PackWriter packer, ProgressMonitor monitor, Iterable<ObjectToPack> objects)
          Select the best object representation for a packer.
 void walkAdviceBeginCommits(RevWalk walk, Collection<RevCommit> roots)
          Advice from a RevWalk that a walk is starting from these roots.
 void walkAdviceBeginTrees(ObjectWalk ow, RevCommit min, RevCommit max)
          Advice from an ObjectWalk that trees will be traversed.
 void walkAdviceEnd()
          Advice from that a walk is over.
 void writeObjects(PackOutputStream out, List<ObjectToPack> list)
          Write objects to the pack stream in roughly the order given.
 
Methods inherited from class org.eclipse.jgit.lib.ObjectReader
abbreviate, abbreviate, has, open
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Method Detail

newReader

public ObjectReader newReader()
Description copied from class: ObjectReader
Construct a new reader from the same data.

Applications can use this method to build a new reader from the same data source, but for an different thread.

Specified by:
newReader in class ObjectReader
Returns:
a brand new reader, using the same data source.

resolve

public Collection<ObjectId> resolve(AbbreviatedObjectId id)
                             throws IOException
Description copied from class: ObjectReader
Resolve an abbreviated ObjectId to its full form. This method searches for an ObjectId that begins with the abbreviation, and returns at least some matching candidates. If the returned collection is empty, no objects start with this abbreviation. The abbreviation doesn't belong to this repository, or the repository lacks the necessary objects to complete it. If the collection contains exactly one member, the abbreviation is (currently) unique within this database. There is a reasonably high probability that the returned id is what was previously abbreviated. If the collection contains 2 or more members, the abbreviation is not unique. In this case the implementation is only required to return at least 2 candidates to signal the abbreviation has conflicts. User friendly implementations should return as many candidates as reasonably possible, as the caller may be able to disambiguate further based on context. However since databases can be very large (e.g. 10 million objects) returning 625,000 candidates for the abbreviation "0" is simply unreasonable, so implementors should draw the line at around 256 matches.

Specified by:
resolve in class ObjectReader
Parameters:
id - abbreviated id to resolve to a complete identity. The abbreviation must have a length of at least 2.
Returns:
candidates that begin with the abbreviated identity.
Throws:
IOException - the object store cannot be read.

has

public boolean has(AnyObjectId objectId)
            throws IOException
Description copied from class: ObjectReader
Does the requested object exist in this database?

Overrides:
has in class ObjectReader
Parameters:
objectId - identity of the object to test for existence of.
Returns:
true if the specified object is stored in this database.
Throws:
IOException - the object store cannot be accessed.

open

public ObjectLoader open(AnyObjectId objectId,
                         int typeHint)
                  throws MissingObjectException,
                         IncorrectObjectTypeException,
                         IOException
Description copied from class: ObjectReader
Open an object from this database.

Specified by:
open in class ObjectReader
Parameters:
objectId - identity of the object to open.
typeHint - hint about the type of object being requested; ObjectReader.OBJ_ANY if the object type is not known, or does not matter to the caller.
Returns:
a ObjectLoader for accessing the object.
Throws:
MissingObjectException - the object does not exist.
IncorrectObjectTypeException - typeHint was not OBJ_ANY, and the object's actual type does not match typeHint.
IOException - the object store cannot be accessed.

getShallowCommits

public Set<ObjectId> getShallowCommits()
Description copied from class: ObjectReader
Returns IDs for those commits which should be considered as shallow.

Specified by:
getShallowCommits in class ObjectReader
Returns:
IDs of shallow commits

open

public <T extends ObjectId> AsyncObjectLoaderQueue<T> open(Iterable<T> objectIds,
                                                           boolean reportMissing)
Description copied from class: ObjectReader
Asynchronous object opening.

Overrides:
open in class ObjectReader
Type Parameters:
T - type of identifier being supplied.
Parameters:
objectIds - objects to open from the object store. The supplied collection must not be modified until the queue has finished.
reportMissing - if true missing objects are reported by calling failure with a MissingObjectException. This may be more expensive for the implementation to guarantee. If false the implementation may choose to report MissingObjectException, or silently skip over the object with no warning.
Returns:
queue to read the objects from.

getObjectSize

public <T extends ObjectId> AsyncObjectSizeQueue<T> getObjectSize(Iterable<T> objectIds,
                                                                  boolean reportMissing)
Description copied from class: ObjectReader
Asynchronous object size lookup.

Overrides:
getObjectSize in class ObjectReader
Type Parameters:
T - type of identifier being supplied.
Parameters:
objectIds - objects to get the size of from the object store. The supplied collection must not be modified until the queue has finished.
reportMissing - if true missing objects are reported by calling failure with a MissingObjectException. This may be more expensive for the implementation to guarantee. If false the implementation may choose to report MissingObjectException, or silently skip over the object with no warning.
Returns:
queue to read object sizes from.

walkAdviceBeginCommits

public void walkAdviceBeginCommits(RevWalk walk,
                                   Collection<RevCommit> roots)
Description copied from class: ObjectReader
Advice from a RevWalk that a walk is starting from these roots.

Overrides:
walkAdviceBeginCommits in class ObjectReader
Parameters:
walk - the revision pool that is using this reader.
roots - starting points of the revision walk. The starting points have their headers parsed, but might be missing bodies.

walkAdviceBeginTrees

public void walkAdviceBeginTrees(ObjectWalk ow,
                                 RevCommit min,
                                 RevCommit max)
Description copied from class: ObjectReader
Advice from an ObjectWalk that trees will be traversed.

Overrides:
walkAdviceBeginTrees in class ObjectReader
Parameters:
ow - the object pool that is using this reader.
min - the first commit whose root tree will be read.
max - the last commit whose root tree will be read.

walkAdviceEnd

public void walkAdviceEnd()
Description copied from class: ObjectReader
Advice from that a walk is over.

Overrides:
walkAdviceEnd in class ObjectReader

getObjectSize

public long getObjectSize(AnyObjectId objectId,
                          int typeHint)
                   throws MissingObjectException,
                          IncorrectObjectTypeException,
                          IOException
Description copied from class: ObjectReader
Get only the size of an object.

The default implementation of this method opens an ObjectLoader. Databases are encouraged to override this if a faster access method is available to them.

Overrides:
getObjectSize in class ObjectReader
Parameters:
objectId - identity of the object to open.
typeHint - hint about the type of object being requested; ObjectReader.OBJ_ANY if the object type is not known, or does not matter to the caller.
Returns:
size of object in bytes.
Throws:
MissingObjectException - the object does not exist.
IncorrectObjectTypeException - typeHint was not OBJ_ANY, and the object's actual type does not match typeHint.
IOException - the object store cannot be accessed.

newObjectToPack

public org.eclipse.jgit.storage.dfs.DfsObjectToPack newObjectToPack(RevObject obj)
Description copied from interface: ObjectReuseAsIs
Allocate a new PackWriter state structure for an object.

PackWriter allocates these objects to keep track of the per-object state, and how to load the objects efficiently into the generated stream. Implementers may subclass this type with additional object state, such as to remember what file and offset contains the object's pack encoded data.

Specified by:
newObjectToPack in interface ObjectReuseAsIs
Parameters:
obj - identity of the object that will be packed. The object's parsed status is undefined here. Implementers must not rely on the object being parsed.
Returns:
a new instance for this object.

selectObjectRepresentation

public void selectObjectRepresentation(PackWriter packer,
                                       ProgressMonitor monitor,
                                       Iterable<ObjectToPack> objects)
                                throws IOException,
                                       MissingObjectException
Description copied from interface: ObjectReuseAsIs
Select the best object representation for a packer.

Implementations should iterate through all available representations of an object, and pass them in turn to the PackWriter though PackWriter.select(ObjectToPack, StoredObjectRepresentation) so the writer can select the most suitable representation to reuse into the output stream.

If the implementation returns CachedPack from ObjectReuseAsIs.getCachedPacks(), it must consider the representation of any object that is stored in any of the offered CachedPacks. PackWriter relies on this behavior to prune duplicate objects out of the pack stream when it selects a CachedPack and the object was also reached through the thin-pack enumeration.

The implementation may choose to consider multiple objects at once on concurrent threads, but must evaluate all representations of an object within the same thread.

Specified by:
selectObjectRepresentation in interface ObjectReuseAsIs
Parameters:
packer - the packer that will write the object in the near future.
monitor - progress monitor, implementation should update the monitor once for each item in the iteration when selection is done.
objects - the objects that are being packed.
Throws:
MissingObjectException - there is no representation available for the object, as it is no longer in the repository. Packing will abort.
IOException - the repository cannot be accessed. Packing will abort.

copyObjectAsIs

public void copyObjectAsIs(PackOutputStream out,
                           ObjectToPack otp,
                           boolean validate)
                    throws IOException,
                           StoredObjectRepresentationNotAvailableException
Description copied from interface: ObjectReuseAsIs
Output a previously selected representation.

PackWriter invokes this method only if a representation previously given to it by selectObjectRepresentation was chosen for reuse into the output stream. The otp argument is an instance created by this reader's own newObjectToPack, and the representation data saved within it also originated from this reader.

Implementors must write the object header before copying the raw data to the output stream. The typical implementation is like:

 MyToPack mtp = (MyToPack) otp;
 byte[] raw;
 if (validate)
         raw = validate(mtp); // throw SORNAE here, if at all
 else
         raw = readFast(mtp);
 out.writeHeader(mtp, mtp.inflatedSize);
 out.write(raw);
 

Specified by:
copyObjectAsIs in interface ObjectReuseAsIs
Parameters:
out - stream the object should be written to.
otp - the object's saved representation information.
validate - if true the representation must be validated and not be corrupt before being reused. If false, validation may be skipped as it will be performed elsewhere in the processing pipeline.
Throws:
IOException - the stream's write method threw an exception. Packing will abort.
StoredObjectRepresentationNotAvailableException - the previously selected representation is no longer available. If thrown before out.writeHeader the pack writer will try to find another representation, and write that one instead. If throw after out.writeHeader, packing will abort.

writeObjects

public void writeObjects(PackOutputStream out,
                         List<ObjectToPack> list)
                  throws IOException
Description copied from interface: ObjectReuseAsIs
Write objects to the pack stream in roughly the order given. PackWriter invokes this method to write out one or more objects, in approximately the order specified by the iteration over the list. A simple implementation of this method would just iterate the list and output each object:
 for (ObjectToPack obj : list)
   out.writeObject(obj)
 
However more sophisticated implementors may try to perform some (small) reordering to access objects that are stored close to each other at roughly the same time. Implementations may choose to write objects out of order, but this may increase pack file size due to using a larger header format to reach a delta base that is later in the stream. It may also reduce data locality for the reader, slowing down data access. Invoking PackOutputStream.writeObject(ObjectToPack) will cause ObjectReuseAsIs.copyObjectAsIs(PackOutputStream, ObjectToPack, boolean) to be invoked recursively on this if the current object is scheduled for reuse.

Specified by:
writeObjects in interface ObjectReuseAsIs
Parameters:
out - the stream to write each object to.
list - the list of objects to write. Objects should be written in approximately this order. Implementors may resort the list elements in-place during writing if desired.
Throws:
IOException - the stream cannot be written to, or one or more required objects cannot be accessed from the object database.

getCachedPacks

public Collection<CachedPack> getCachedPacks()
                                      throws IOException
Description copied from interface: ObjectReuseAsIs
Obtain the available cached packs.

A cached pack has known starting points and may be sent entirely as-is, with almost no effort on the sender's part.

Specified by:
getCachedPacks in interface ObjectReuseAsIs
Returns:
the available cached packs.
Throws:
IOException - the cached packs cannot be listed from the repository. Callers may choose to ignore this and continue as-if there were no cached packs.

copyPackAsIs

public void copyPackAsIs(PackOutputStream out,
                         CachedPack pack,
                         boolean validate)
                  throws IOException
Description copied from interface: ObjectReuseAsIs
Append an entire pack's contents onto the output stream.

The entire pack, excluding its header and trailing footer is sent.

Specified by:
copyPackAsIs in interface ObjectReuseAsIs
Parameters:
out - stream to append the pack onto.
pack - the cached pack to send.
validate - if true the representation must be validated and not be corrupt before being reused. If false, validation may be skipped as it will be performed elsewhere in the processing pipeline.
Throws:
IOException - the pack cannot be read, or stream did not accept a write.

release

public void release()
Release the current window cursor.

Overrides:
release in class ObjectReader


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