Keep output of experimental UI short if curses cannot be used

As the experimental UI should be usable in all situations, we also have
to care about the situation where updating the status bar in place is not
possible. In this case, we have to make sure we do not litter the output
to much. To achieve this,
- we use the short one-line version of the status bar, and
- reduce the frequency for time-based updates.
Unfortunately, this means that we have to further complicate the timing mechanisms
for updating the progress bar. We now have 3 time intervals in place:
- a short one, after which we update the progress bar, if we dropped an update
  due to too frequent events,
- an intermediate one, describing the frequency of status bar updates due to time passing, and
- a long one for purely time-based updates of the progress bar if we cannot update it in place.

--
Change-Id: I5d59ba174c4d290b07181620e238362a8d21a6eb
Reviewed-on: https://bazel-review.googlesource.com/#/c/3295
MOS_MIGRATED_REVID=119527089

1 files changed, 22 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
index b852de611a..052d6cbb44 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/ExperimentalEventHandler.java
@@ -42,6 +42,12 @@ import java.util.logging.Logger;
  */
 public class ExperimentalEventHandler extends BlazeCommandEventHandler {
   private static Logger LOG = Logger.getLogger(ExperimentalEventHandler.class.getName());
+  /** Latest refresh of the progress bar, if contents other than time changed */
+  static final long MAXIMAL_UPDATE_DELAY_MILLIS = 200L;
+  /** Periodic update interval of a time-dependent progress bar if it can be updated in place */
+  static final long SHORT_REFRESH_MILLIS = 1000L;
+  /** Periodic update interval of a time-dependent progress bar if it cannot be updated in place */
+  static final long LONG_REFRESH_MILLIS = 5000L;
 
   private final long minimalDelayMillis;
   private final boolean cursorControl;
@@ -69,7 +75,7 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
     this.stateTracker = new ExperimentalStateTracker(clock);
     this.numLinesProgressBar = 0;
     this.minimalDelayMillis = Math.round(options.showProgressRateLimit * 1000);
-    this.minimalUpdateInterval = Math.max(this.minimalDelayMillis, 1000L);
+    this.minimalUpdateInterval = Math.max(this.minimalDelayMillis, MAXIMAL_UPDATE_DELAY_MILLIS);
     // The progress bar has not been updated yet.
     ignoreRefreshLimitOnce();
   }
@@ -229,7 +235,7 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
     long nowMillis = clock.currentTimeMillis();
     if (lastRefreshMillis + minimalDelayMillis < nowMillis) {
       try {
-        if (progressBarNeedsRefresh || stateTracker.progressBarTimeDependent()) {
+        if (progressBarNeedsRefresh || timeBasedRefresh()) {
           progressBarNeedsRefresh = false;
           lastRefreshMillis = nowMillis;
           clearProgressBar();
@@ -250,6 +256,19 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
     }
   }
 
+  /**
+   * Decide wheter the progress bar should be redrawn only for the reason
+   * that time has passed.
+   */
+  private synchronized boolean timeBasedRefresh () {
+    if (!stateTracker.progressBarTimeDependent()) {
+      return false;
+    }
+    long nowMillis = clock.currentTimeMillis();
+    long intervalMillis = cursorControl ? SHORT_REFRESH_MILLIS : LONG_REFRESH_MILLIS;
+    return lastRefreshMillis + intervalMillis < nowMillis;
+  }
+
   private void ignoreRefreshLimitOnce() {
     // Set refresh time variables in a state such that the next progress bar
     // update will definitely be written out.
@@ -322,7 +341,7 @@ public class ExperimentalEventHandler extends BlazeCommandEventHandler {
     if (cursorControl) {
       terminalWriter = new LineWrappingAnsiTerminalWriter(terminalWriter, terminalWidth - 1);
     }
-    stateTracker.writeProgressBar(terminalWriter);
+    stateTracker.writeProgressBar(terminalWriter, /* shortVersion=*/ !cursorControl);
     terminalWriter.newline();
     numLinesProgressBar = countingTerminalWriter.getWrittenLines();
   }