ProgressMonitor: Refactor to use background alarms

Instead of polling the system clock on every update(1) method call,
use a scheduled executor to toggle a volatile once per second until
the task is done.  Check the volatile on each update(int), looking
to see if output should occur.

This limits progress output to either once per 1% complete, or once
per second.  To save time during update calls the timer isn't reset
during each 1% of output, which means we may see one unnecessary
output trigger if at least 1% completed during the one second of the
alarm time.

Change-Id: I8fdd7e31c37bef39a5d1b3da7105da0ef879eb84
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Diff.java b/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Diff.java
index 506031713a..5cc058950c 100644
--- a/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Diff.java
+++ b/org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Diff.java
@@ -52,6 +52,7 @@ import java.io.BufferedOutputStream;
 import java.io.PrintWriter;
 import java.text.MessageFormat;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
 
 import org.eclipse.jgit.diff.DiffAlgorithm;
 import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
@@ -189,7 +190,9 @@ class Diff extends TextBuiltin {
 			} else if (newTree == null)
 				newTree = new FileTreeIterator(db);
 
-			diffFmt.setProgressMonitor(new TextProgressMonitor());
+			TextProgressMonitor pm = new TextProgressMonitor();
+			pm.setDelayStart(2, TimeUnit.SECONDS);
+			diffFmt.setProgressMonitor(pm);
 			diffFmt.setPathFilter(pathFilter);
 			if (detectRenames != null)
 				diffFmt.setDetectRenames(detectRenames.booleanValue());