Fix FileSnapShot

We cannot use SystemReader to get the time, unless we do that consistently,
which is harder to do and be sure we are really testing what we want.

Then we need to update our lastRead variable whenever we conclude that
our file is not racily clean according to lastRead. It may well be clean,
but we do not know that until we check the system clock again.

Finally add a test for this class.

Change-Id: I1894b032b9bd359d1b5325e5472d48e372599e4c
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/storage/file/FileSnapshotTest.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2010, Robin Rosenberg
+ * 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 java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.eclipse.jgit.util.FileUtils;
+import org.junit.Before;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class FileSnapshotTest {
+
+	private List<File> files = new ArrayList<File>();
+
+	private final File trash = new File(new File("target"), "trash");
+
+	@Before
+	public void tearDown() throws Exception {
+		FileUtils.delete(trash, FileUtils.RECURSIVE | FileUtils.SKIP_MISSING);
+	}
+
+	private void waitNextSec(File f) {
+		long initialLastModified = f.lastModified();
+		do {
+			f.setLastModified(System.currentTimeMillis());
+		} while (f.lastModified() == initialLastModified);
+	}
+
+	/**
+	 * Change data and time stamp.
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	public void testActuallyIsModifiedTrivial() throws Exception {
+		File f1 = createFile("simple");
+		waitNextSec(f1);
+		FileSnapshot save = FileSnapshot.save(f1);
+		append(f1, (byte) 'x');
+		waitNextSec(f1);
+		assertTrue(save.isModified(f1));
+	}
+
+	/**
+	 * Create a file, wait long enough and verify that it has not been modified.
+	 * 3.5 seconds mean any difference between file system timestamp and system
+	 * clock should be significant.
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	public void testOldFile() throws Exception {
+		File f1 = createFile("oldfile");
+		waitNextSec(f1);
+		FileSnapshot save = FileSnapshot.save(f1);
+		Thread.sleep(3500);
+		assertFalse(save.isModified(f1));
+	}
+
+	/**
+	 * Create a file, but don't wait long enough for the difference between file
+	 * system clock and system clock to be significant. Assume the file may have
+	 * been modified. It may have been, but the clock alone cannot determine
+	 * this
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	public void testNewFileWithWait() throws Exception {
+		File f1 = createFile("newfile");
+		waitNextSec(f1);
+		FileSnapshot save = FileSnapshot.save(f1);
+		Thread.sleep(1500);
+		assertTrue(save.isModified(f1));
+	}
+
+	/**
+	 * Same as {@link #testNewFileWithWait()} but do not wait at all
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	public void testNewFileNoWait() throws Exception {
+		File f1 = createFile("newfile");
+		waitNextSec(f1);
+		FileSnapshot save = FileSnapshot.save(f1);
+		Thread.sleep(1500);
+		assertTrue(save.isModified(f1));
+	}
+
+	private File createFile(String string) throws IOException {
+		trash.mkdirs();
+		File f = File.createTempFile(string, "tdat", trash);
+		files.add(f);
+		return f;
+	}
+
+	private void append(File f, byte b) throws IOException {
+		FileOutputStream os = new FileOutputStream(f, true);
+		try {
+			os.write(b);
+		} finally {
+			os.close();
+		}
+	}
+
+}

org.eclipse.jgit/src/org/eclipse/jgit/storage/file/FileSnapshot.java

@@ -45,8 +45,6 @@ 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>
@@ -84,7 +82,7 @@ public class FileSnapshot {
 	 * @return the snapshot.
 	 */
 	public static FileSnapshot save(File path) {
-		final long read = SystemReader.getInstance().getCurrentTime();
+		final long read = System.currentTimeMillis();
 		final long modified = path.lastModified();
 		return new FileSnapshot(read, modified);
 	}
@@ -109,8 +107,8 @@ public class FileSnapshot {
 	}
 
 	/**
-	 * Check if the path has been modified since the snapshot was saved.
-	 *
+	 * Check if the path may have been modified since the snapshot was saved.
+	 * 
 	 * @param path
 	 *            the path the snapshot describes.
 	 * @return true if the path needs to be read again.
@@ -203,6 +201,12 @@ public class FileSnapshot {
 			return false;
 		}
 
+		// Our lastRead flag may be old, refresh and retry
+		lastRead = System.currentTimeMillis();
+		if (notRacyClean(lastRead)) {
+			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.