Define MonotonicClock interface for advanced timestamps

MonotonicClock can be implemented to provide more certainity about
time than the standard System.currentTimeMillis() can provide. This
can be used by classes such as PersonIdent and Ketch to rely on
more certainity about time moving in a strictly ascending order.

Gerrit Code Review can also leverage this interface through its
embedding of JGit and use MonotonicClock and ProposedTimestamp to
provide stronger assurance that NoteDb time is moving forward.

Change-Id: I1a3cbd49a39b150a0d49b36d572da113ca83a786

3 files changed, 115 insertions, 5 deletions

diff --git a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
index c27d03d298..dc2e8bfb71 100644
--- a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
+++ b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/LocalDiskRepositoryTestCase.java
@@ -122,13 +122,8 @@ public abstract class LocalDiskRepositoryTestCase {
 		ceilTestDirectories(getCeilings());
 		SystemReader.setInstance(mockSystemReader);
 
-		final long now = mockSystemReader.getCurrentTime();
-		final int tz = mockSystemReader.getTimezone(now);
 		author = new PersonIdent("J. Author", "jauthor@example.com");
-		author = new PersonIdent(author, now, tz);
-
 		committer = new PersonIdent("J. Committer", "jcommitter@example.com");
-		committer = new PersonIdent(committer, now, tz);
 
 		final WindowCacheConfig c = new WindowCacheConfig();
 		c.setPackedGitLimit(128 * WindowCacheConfig.KB);
diff --git a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
index 28a95569e8..6faa2ece48 100644
--- a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
+++ b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/MockSystemReader.java
@@ -50,10 +50,12 @@ import java.io.IOException;
 import java.lang.reflect.Field;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
+import java.time.Duration;
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
 
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.lib.Config;
@@ -61,6 +63,8 @@ import org.eclipse.jgit.lib.Constants;
 import org.eclipse.jgit.storage.file.FileBasedConfig;
 import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.SystemReader;
+import org.eclipse.jgit.util.time.MonotonicClock;
+import org.eclipse.jgit.util.time.ProposedTimestamp;
 
 /**
  * Mock {@link SystemReader} for tests.
@@ -146,6 +150,27 @@ public class MockSystemReader extends SystemReader {
 		return now;
 	}
 
+	@Override
+	public MonotonicClock getClock() {
+		return new MonotonicClock() {
+			@Override
+			public ProposedTimestamp propose() {
+				long t = getCurrentTime();
+				return new ProposedTimestamp() {
+					@Override
+					public long read(TimeUnit unit) {
+						return unit.convert(t, TimeUnit.MILLISECONDS);
+					}
+
+					@Override
+					public void blockUntil(Duration maxWait) {
+						// Do not wait.
+					}
+				};
+			}
+		};
+	}
+
 	/**
 	 * Adjusts the current time in seconds.
 	 *
diff --git a/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/time/MonotonicFakeClock.java b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/time/MonotonicFakeClock.java
new file mode 100644
index 0000000000..f09d303d55
--- /dev/null
+++ b/org.eclipse.jgit.junit/src/org/eclipse/jgit/junit/time/MonotonicFakeClock.java
@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2016, 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.junit.time;
+
+import java.time.Duration;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jgit.util.time.MonotonicClock;
+import org.eclipse.jgit.util.time.ProposedTimestamp;
+
+/**
+ * Fake {@link MonotonicClock} for testing code that uses Clock.
+ *
+ * @since 4.6
+ */
+public class MonotonicFakeClock implements MonotonicClock {
+	private long now = TimeUnit.SECONDS.toMicros(42);
+
+	/**
+	 * Advance the time returned by future calls to {@link #propose()}.
+	 *
+	 * @param add
+	 *            amount of time to add; must be {@code > 0}.
+	 * @param unit
+	 *            unit of {@code add}.
+	 */
+	public void tick(long add, TimeUnit unit) {
+		if (add <= 0) {
+			throw new IllegalArgumentException();
+		}
+		now += unit.toMillis(add);
+	}
+
+	@Override
+	public ProposedTimestamp propose() {
+		long t = now++;
+		return new ProposedTimestamp() {
+			@Override
+			public long read(TimeUnit unit) {
+				return unit.convert(t, TimeUnit.MILLISECONDS);
+			}
+
+			@Override
+			public void blockUntil(Duration maxWait) {
+				// Nothing to do, since fake time does not go backwards.
+			}
+		};
+	}
+}