tests: fix flaky SkyframeAwareActionTest

Fix testCacheBypassingActionWithMtimeChangingInput
in SkyframeAwareActionTest by ensuring that enough
time elapses between file updates so their effects
are observable on the file's ctime.

Fixes https://github.com/bazelbuild/bazel/issues/4755

Closes #4787.

PiperOrigin-RevId: 188458542

1 files changed, 24 insertions, 4 deletions

diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
index bc206657e6..e521a54f35 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/SkyframeAwareActionTest.java
@@ -334,19 +334,39 @@ public class SkyframeAwareActionTest extends TimestampBuilderTestCase {
     }
   }
 
+  /** Sanity check: ensure that a file's ctime was updated from an older value. */
+  private void checkCtimeUpdated(Path path, long oldCtime) throws IOException {
+    if (oldCtime >= path.stat().getLastChangeTime()) {
+      throw new IllegalStateException(String.format("path=(%s), ctime=(%d)", path, oldCtime));
+    }
+  }
+
   private void maybeChangeFile(Artifact file, ChangeArtifact changeRequest) throws Exception {
     if (changeRequest == ChangeArtifact.DONT_CHANGE) {
       return;
     }
 
+    Path path = file.getPath();
+
     if (changeRequest.changeMtime()) {
-      // 1000000 should be larger than the filesystem timestamp granularity.
-      file.getPath().setLastModifiedTime(file.getPath().getLastModifiedTime() + 1000000);
-      tsgm.waitForTimestampGranularity(reporter.getOutErr());
+      long ctime = path.stat().getLastChangeTime();
+      // Ensure enough time elapsed for file updates to have a visible effect on the file's ctime.
+      tsgm.waitForTimestampGranularity(ctime, reporter.getOutErr());
+      // waitForTimestampGranularity waits long enough for System.currentTimeMillis() to be greater
+      // than the time at the setCommandStartTime() call. Therefore setting
+      // System.currentTimeMillis() is guaranteed to advance the file's ctime.
+      path.setLastModifiedTime(System.currentTimeMillis());
+      // Sanity check: ensure that updating the file's mtime indeed advanced its ctime.
+      checkCtimeUpdated(path, ctime);
     }
 
     if (changeRequest.changeContent()) {
-      appendToFile(file.getPath());
+      long ctime = path.stat().getLastChangeTime();
+      // Ensure enough time elapsed for file updates to have a visible effect on the file's ctime.
+      tsgm.waitForTimestampGranularity(ctime, reporter.getOutErr());
+      appendToFile(path);
+      // Sanity check: ensure that appending to the file indeed advanced its ctime.
+      checkCtimeUpdated(path, ctime);
     }
 
     // Invalidate the file state value to inform Skyframe that the file may have changed.