Add new performance logging

Add new performance logging to register events of type duration.
The proposed logging is similar to the performance logging
in OS Gerrit https://gerrit-review.googlesource.com/c/gerrit/+/225628:
a global Singleton (LoggingContext in Gerrit) is
collecting the performance logs in a thread-safe events list,
and at the end of the monitored command the list of events is
retrieved and written to a log, after which it is cleared.

What this patch does:
The main component is the Singleton (PerformanceLogContext), which
is used to collect the records (PerformanceLogRecord) in one place
(ThreadLocal eventsList) from anywhere using
PerformanceLogContext.getInstance().addEvent().

Reason why this change is needed:
The current monitoring in JGit has several issues:
1. git fetch and git push events are handled separately
(PackStatistics and ReceivedPackStatistics), with no unified way
of writing or reading the statistics.
2. PostUploadHook is only invoked on the event of sending the
pack, which means that the PackStatistics is not available for
the fetch requests that did not end with sending the pack
(negotiation requests).
3. The way the logs are created is different from the performance
log approach, so the long-running operations need to be collected
from both performance log (for JGit DFS overridden operations and
Gerrit operations) and gitlog (for JGit ones).

The proposed performance logging is going to solve the above
mentioned issues: it collects all of the performance logs in one
place, thus accounting for the commands that do not result in
sending a pack. The logs are compatible with the ones on Gerrit.
Moreover, the Singleton is accessible anywhere in the call stack,
which proved to be successful in other projects like Dapper
(https://research.google/pubs/pub36356/).

Signed-off-by: Alexa Panfil <alexapizza@google.com>
Change-Id: Iabfe667a3412d8a9db94aabb0f39b57f43469c41

1 files changed, 66 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/logging/PerformanceLogContextTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/logging/PerformanceLogContextTest.java
new file mode 100644
index 0000000000..e061833d17
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/logging/PerformanceLogContextTest.java
@@ -0,0 +1,66 @@
+package org.eclipse.jgit.logging;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+import java.util.List;
+
+/**
+ * Tests for performance log context utilities.
+ */
+public class PerformanceLogContextTest {
+
+	@Test
+	public void testAddEvent() {
+		PerformanceLogRecord record = new PerformanceLogRecord("record", 0);
+		PerformanceLogContext.getInstance().addEvent(record);
+
+		List<PerformanceLogRecord> eventRecords = PerformanceLogContext
+				.getInstance().getEventRecords();
+		assertTrue(eventRecords.contains(record));
+		assertEquals(1, eventRecords.size());
+	}
+
+	@Test
+	public void testCleanEvents() {
+		PerformanceLogRecord record1 = new PerformanceLogRecord("record1", 0);
+		PerformanceLogContext.getInstance().addEvent(record1);
+
+		PerformanceLogRecord record2 = new PerformanceLogRecord("record2", 0);
+		PerformanceLogContext.getInstance().addEvent(record2);
+
+		PerformanceLogContext.getInstance().cleanEvents();
+		List<PerformanceLogRecord> eventRecords = PerformanceLogContext
+				.getInstance().getEventRecords();
+		assertEquals(0, eventRecords.size());
+	}
+
+	@Test
+	public void testAddEventsTwoThreads() {
+		TestRunnable thread1 = new TestRunnable("record1", 1);
+		TestRunnable thread2 = new TestRunnable("record2", 2);
+
+		new Thread(thread1).start();
+		new Thread(thread2).start();
+	}
+
+	private static class TestRunnable implements Runnable {
+		private String name;
+		private long durationMs;
+
+		public TestRunnable(String name, long durationMs) {
+			this.name = name;
+			this.durationMs = durationMs;
+		}
+
+		@Override
+		public void run() {
+			PerformanceLogRecord record = new PerformanceLogRecord(name,
+					durationMs);
+			PerformanceLogContext.getInstance().addEvent(record);
+			assertEquals(1, PerformanceLogContext.getInstance()
+					.getEventRecords().size());
+		}
+	}
+}