github
/
jgit
mirror of https://gitee.com/github-mirror-repo/jgit.git
1
0
Fork 0
Code Issues Releases Wiki Activity
Browse Source

Extract pack directory last modified check code 

Pulling the last modified checking logic out of ObjectDirectory
makes it possible to reuse this code for other files, such as
the $GIT_DIR/config or $GIT_DIR/packed-refs files.

Change-Id: If2f27a89fc3b7adde7e65ff40bbca5d55b98b772
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
stable-0.11
Shawn O. Pearce 14 years ago
parent
6f3b4d5d04
commit
c8db22f355
2 changed files with 224 additions and 61 deletions
Whitespace
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
Unified View
Diff Options
Show Stats Download Patch File Download Diff File
  1. 208
      org.eclipse.jgit/src/org/eclipse/jgit/storage/file/FileSnapshot.java
  2. 77
      org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java

208
org.eclipse.jgit/src/org/eclipse/jgit/storage/file/FileSnapshot.java
Unescape View File

@ -0,0 +1,208 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* - Neither the name of the Eclipse Foundation, Inc. nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.eclipse.jgit.storage.file;
import java.io.File;
import org.eclipse.jgit.util.SystemReader;
/**
* Caches when a file was last read, making it possible to detect future edits.
* <p>
* This object tracks the last modified time of a file. Later during an
* invocation of {@link #isModified(File)} the object will return true if the
* file may have been modified and should be re-read from disk.
* <p>
* A snapshot does not "live update" when the underlying filesystem changes.
* Callers must poll for updates by periodically invoking
* {@link #isModified(File)}.
* <p>
* 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.
*/
public class FileSnapshot {
/**
* A FileSnapshot that is considered to always be modified.
* <p>
* This instance is useful for application code that wants to lazily read a
* file, but only after {@link #isModified(File)} gets invoked. The returned
* snapshot contains only invalid status information.
*/
public static final FileSnapshot DIRTY = new FileSnapshot(-1, -1);
/**
* Record a snapshot for a specific file path.
* <p>
* This method should be invoked before the file is accessed.
*
* @param path
* the path to later remember. The path's current status
* information is saved.
* @return the snapshot.
*/
public static FileSnapshot save(File path) {
final long read = SystemReader.getInstance().getCurrentTime();
final long modified = path.lastModified();
return new FileSnapshot(read, modified);
}
/** Last observed modification time of the path. */
private final long lastModified;
/** Last wall-clock time the path was read. */
private volatile long lastRead;
/** True once {@link #lastRead} is far later than {@link #lastModified}. */
private boolean cannotBeRacilyClean;
private FileSnapshot(long read, long modified) {
this.lastRead = read;
this.lastModified = modified;
this.cannotBeRacilyClean = notRacyClean(read);
}
/**
* Check if the path has been modified since the snapshot was saved.
*
* @param path
* the path the snapshot describes.
* @return true if the path needs to be read again.
*/
public boolean isModified(File path) {
return isModified(path.lastModified());
}
/**
* Update this snapshot when the content hasn't changed.
* <p>
* If the caller gets true from {@link #isModified(File)}, re-reads the
* content, discovers the content is identical, and
* {@link #equals(FileSnapshot)} is true, it can use
* {@link #setClean(FileSnapshot)} to make a future
* {@link #isModified(File)} return false. The logic goes something like
* this:
*
* <pre>
* if (snapshot.isModified(path)) {
* FileSnapshot other = FileSnapshot.save(path);
* Content newContent = ...;
* if (oldContent.equals(newContent) &amp;&amp; snapshot.equals(other))
* snapshot.setClean(other);
* }
* </pre>
*
* @param other
* the other snapshot.
*/
public void setClean(FileSnapshot other) {
final long now = other.lastRead;
if (notRacyClean(now))
cannotBeRacilyClean = true;
lastRead = now;
}
/**
* Compare two snapshots to see if they cache the same information.
*
* @param other
* the other snapshot.
* @return true if the two snapshots share the same information.
*/
public boolean equals(FileSnapshot other) {
return lastModified == other.lastModified;
}
@Override
public boolean equals(Object other) {
if (other instanceof FileSnapshot)
return equals((FileSnapshot) other);
return false;
}
@Override
public int hashCode() {
// This is pretty pointless, but override hashCode to ensure that
// x.hashCode() == y.hashCode() when x.equals(y) is true.
//
return (int) lastModified;
}
private boolean notRacyClean(final long read) {
// The last modified time granularity of FAT filesystems is 2 seconds.
// Using 2.5 seconds here provides a reasonably high assurance that
// a modification was not missed.
//
return read - lastModified > 2500;
}
private boolean isModified(final long currLastModified) {
// Any difference indicates the path was modified.
//
if (lastModified != currLastModified)
return true;
// We have already determined the last read was far enough
// after the last modification that any new modifications
// are certain to change the last modified time.
//
if (cannotBeRacilyClean)
return false;
if (notRacyClean(lastRead)) {
// Our last read should have marked cannotBeRacilyClean,
// but this thread may not have seen the change. The read
// of the volatile field lastRead should have fixed that.
//
return false;
}
// We last read this path too close to its last observed
// modification time. We may have missed a modification.
// Scan again, to ensure we still see the same state.
//
return true;
}
}

77
org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java
Unescape View File

@ -96,7 +96,8 @@ import org.eclipse.jgit.util.FileUtils;
* considered. * considered.
*/ */
public class ObjectDirectory extends FileObjectDatabase { public class ObjectDirectory extends FileObjectDatabase {
private static final PackList NO_PACKS = new PackList(-1, -1, new PackFile[0]); private static final PackList NO_PACKS = new PackList(
FileSnapshot.DIRTY, new PackFile[0]);
/** Maximum number of candidates offered as resolutions of abbreviation. */ /** Maximum number of candidates offered as resolutions of abbreviation. */
private static final int RESOLVE_ABBREV_LIMIT = 256; private static final int RESOLVE_ABBREV_LIMIT = 256;
@ -509,7 +510,7 @@ public class ObjectDirectory extends FileObjectDatabase {
boolean tryAgain1() { boolean tryAgain1() {
final PackList old = packList.get(); final PackList old = packList.get();
if (old.tryAgain(packDirectory.lastModified())) if (old.snapshot.isModified(packDirectory))
return old != scanPacks(old); return old != scanPacks(old);
return false; return false;
} }
@ -539,7 +540,7 @@ public class ObjectDirectory extends FileObjectDatabase {
final PackFile[] newList = new PackFile[1 + oldList.length]; final PackFile[] newList = new PackFile[1 + oldList.length];
newList[0] = pf; newList[0] = pf;
System.arraycopy(oldList, 0, newList, 1, oldList.length); System.arraycopy(oldList, 0, newList, 1, oldList.length);
n = new PackList(o.lastRead, o.lastModified, newList); n = new PackList(o.snapshot, newList);
} while (!packList.compareAndSet(o, n)); } while (!packList.compareAndSet(o, n));
} }
@ -556,7 +557,7 @@ public class ObjectDirectory extends FileObjectDatabase {
final PackFile[] newList = new PackFile[oldList.length - 1]; final PackFile[] newList = new PackFile[oldList.length - 1];
System.arraycopy(oldList, 0, newList, 0, j); System.arraycopy(oldList, 0, newList, 0, j);
System.arraycopy(oldList, j + 1, newList, j, newList.length - j); System.arraycopy(oldList, j + 1, newList, j, newList.length - j);
n = new PackList(o.lastRead, o.lastModified, newList); n = new PackList(o.snapshot, newList);
} while (!packList.compareAndSet(o, n)); } while (!packList.compareAndSet(o, n));
deadPack.close(); deadPack.close();
} }
@ -590,8 +591,7 @@ public class ObjectDirectory extends FileObjectDatabase {
private PackList scanPacksImpl(final PackList old) { private PackList scanPacksImpl(final PackList old) {
final Map<String, PackFile> forReuse = reuseMap(old); final Map<String, PackFile> forReuse = reuseMap(old);
final long lastRead = System.currentTimeMillis(); final FileSnapshot snapshot = FileSnapshot.save(packDirectory);
final long lastModified = packDirectory.lastModified();
final Set<String> names = listPackDirectory(); final Set<String> names = listPackDirectory();
final List<PackFile> list = new ArrayList<PackFile>(names.size() >> 2); final List<PackFile> list = new ArrayList<PackFile>(names.size() >> 2);
boolean foundNew = false; boolean foundNew = false;
@ -628,19 +628,21 @@ public class ObjectDirectory extends FileObjectDatabase {
// the same as the set we were given. Instead of building a new object // the same as the set we were given. Instead of building a new object
// return the same collection. // return the same collection.
// //
if (!foundNew && lastModified == old.lastModified && forReuse.isEmpty()) if (!foundNew && forReuse.isEmpty() && snapshot.equals(old.snapshot)) {
return old.updateLastRead(lastRead); old.snapshot.setClean(snapshot);
return old;
}
for (final PackFile p : forReuse.values()) { for (final PackFile p : forReuse.values()) {
p.close(); p.close();
} }
if (list.isEmpty()) if (list.isEmpty())
return new PackList(lastRead, lastModified, NO_PACKS.packs); return new PackList(snapshot, NO_PACKS.packs);
final PackFile[] r = list.toArray(new PackFile[list.size()]); final PackFile[] r = list.toArray(new PackFile[list.size()]);
Arrays.sort(r, PackFile.SORT); Arrays.sort(r, PackFile.SORT);
return new PackList(lastRead, lastModified, r); return new PackList(snapshot, r);
} }
private static Map<String, PackFile> reuseMap(final PackList old) { private static Map<String, PackFile> reuseMap(final PackList old) {
@ -737,62 +739,15 @@ public class ObjectDirectory extends FileObjectDatabase {
} }
private static final class PackList { private static final class PackList {
/** Last wall-clock time the directory was read. */ /** State just before reading the pack directory. */
volatile long lastRead; final FileSnapshot snapshot;
/** Last modification time of {@link ObjectDirectory#packDirectory}. */
final long lastModified;
/** All known packs, sorted by {@link PackFile#SORT}. */ /** All known packs, sorted by {@link PackFile#SORT}. */
final PackFile[] packs; final PackFile[] packs;
private boolean cannotBeRacilyClean; PackList(final FileSnapshot monitor, final PackFile[] packs) {
this.snapshot = monitor;
PackList(final long lastRead, final long lastModified,
final PackFile[] packs) {
this.lastRead = lastRead;
this.lastModified = lastModified;
this.packs = packs; this.packs = packs;
this.cannotBeRacilyClean = notRacyClean(lastRead);
}
private boolean notRacyClean(final long read) {
return read - lastModified > 2 * 60 * 1000L;
}
PackList updateLastRead(final long now) {
if (notRacyClean(now))
cannotBeRacilyClean = true;
lastRead = now;
return this;
}
boolean tryAgain(final long currLastModified) {
// Any difference indicates the directory was modified.
//
if (lastModified != currLastModified)
return true;
// We have already determined the last read was far enough
// after the last modification that any new modifications
// are certain to change the last modified time.
//
if (cannotBeRacilyClean)
return false;
if (notRacyClean(lastRead)) {
// Our last read should have marked cannotBeRacilyClean,
// but this thread may not have seen the change. The read
// of the volatile field lastRead should have fixed that.
//
return false;
}
// We last read this directory too close to its last observed
// modification time. We may have missed a modification. Scan
// the directory again, to ensure we still see the same state.
//
return true;
} }
} }

Write Preview
Loading…
Cancel
Save