gh-160735: Fix Gecko marker end times during binary replay

Lib/profiling/sampling/gecko_collector.py

@@ -245,10 +245,9 @@ def collect(self, stack_frames, timestamps_us=None):
 
         first_time = times[0]
 
-        # Update interval calculation
-        if self.sample_count > 0 and self.last_sample_time > 0:
-            self.interval = (times[-1] - self.last_sample_time) / self.sample_count
-        self.last_sample_time = times[-1]
+        # Binary replay can deliver batches from different threads out of
+        # order, so keep the latest time seen rather than the last one.
+        self.last_sample_time = max(self.last_sample_time, times[-1])
 
         # Process async tasks
         if stack_frames and hasattr(stack_frames[0], "awaited_by"):
@@ -732,9 +731,6 @@ def _finalize_markers(self):
 
     def export(self, filename):
         """Export the profile to a Gecko JSON file."""
-        if self.sample_count > 0 and self.last_sample_time > 0:
-            self.interval = self.last_sample_time / self.sample_count
-
         # Spinner for progress indication
         spinner = itertools.cycle(['⠋', '⠙', '⠹', '⠸', '⠼', '⠴', '⠦', '⠧', '⠇', '⠏'])
         stop_spinner = threading.Event()
@@ -864,6 +860,8 @@ def _profile_tail(self):
     def _prepare_for_serialization(self):
         if self.exported:
             raise RuntimeError("GeckoCollector has already been exported")
+        if self.sample_count > 0 and self.last_sample_time > 0:
+            self.interval = self.last_sample_time / self.sample_count
         self._finalize_markers()
         for thread_data in self.threads.values():
             thread_data["_spill"].prepare_read()

Lib/test/test_profiling/test_sampling_profiler/test_collectors.py

@@ -1072,6 +1072,38 @@ def test_gecko_collector_markers(self):
                 f"Marker {i} should have valid category",
             )
 
+    def test_gecko_collector_replay_out_of_order_batches(self):
+        """Open markers are closed at the latest replayed sample."""
+        collector = GeckoCollector(1000)
+        # Binary replay can send thread 2's last batch after thread 1's later
+        # samples
+        batches = [
+            (1, [1000], THREAD_STATUS_ON_CPU),
+            (2, [1500], 0),
+            (1, [2000], THREAD_STATUS_ON_CPU),
+            (1, [3000, 4000], 0),
+            (2, [2500], 0),
+        ]
+        for tid, timestamps, status in batches:
+            frames = [MockFrameInfo(f"t{tid}.py", 10, f"func{tid}")]
+            collector.collect(
+                [MockInterpreterInfo(0, [MockThreadInfo(tid, frames, status=status)])],
+                timestamps_us=timestamps,
+            )
+
+        profile_data = collector._build_profile()
+
+        end_times = []
+        for thread_data in profile_data["threads"]:
+            markers = thread_data["markers"]
+            for start_time, end_time in zip(markers["startTime"],
+                                            markers["endTime"]):
+                self.assertLessEqual(start_time, end_time)
+                end_times.append(end_time)
+        self.assertEqual(max(end_times), 3.0)
+        # Six samples up to 3.0 ms
+        self.assertEqual(profile_data["meta"]["interval"], 0.5)
+
     def test_pstats_collector_export(self):
         collector = PstatsCollector(
             sample_interval_usec=1000000

Misc/NEWS.d/next/Library/2026-10-26-21-14-17.gh-issue-160735.IIUifI.rst

@@ -0,0 +1,2 @@
+Fix Tachyon's Gecko export closing open markers too early when replaying a
+binary profile whose thread samples arrive out of time order.