gh-158550: _remote_debugging: Do not advance prev_timestamp when write_sample fails

Lib/test/test_profiling/test_sampling_profiler/test_binary_format.py

@@ -952,6 +952,26 @@ def test_writer_handles_mixed_empty_and_real_first_sample(self):
         self.assertIn((0, 1), reader_collector.by_thread)
         self.assertEqual(len(reader_collector.by_thread[(0, 1)]), 2)
 
+    def test_writer_failed_sample_does_not_advance_timestamp(self):
+        """A rejected frame must not shift later timestamps."""
+        with tempfile.NamedTemporaryFile(suffix=".bin", delete=False) as f:
+            filename = f.name
+        self.temp_files.append(filename)
+
+        good = [make_interpreter(0, [make_thread(1, [make_frame("a.py", 1, "f")])])]
+        bad = [make_interpreter(0, [make_thread(1, [make_frame(42, 1, "f")])])]
+
+        with _remote_debugging.BinaryWriter(filename, 1000, 0) as writer:
+            writer.write_sample(good, 1000)
+            with self.assertRaises(TypeError):
+                writer.write_sample(bad, 5000)
+            writer.write_sample(good, 6000)
+
+        collector = TimestampCollector()
+        with BinaryReader(filename) as reader:
+            reader.replay_samples(collector)
+        self.assertEqual(collector.all_timestamps, [1000, 6000])
+
     def test_writer_total_samples_after_finalize_matches_reader(self):
         """BinaryWriter.total_samples after finalize() matches the reader's count."""
         # Five IDENTICAL samples force every sample beyond the first into the

Misc/NEWS.d/next/Library/2026-10-01-09-17-11.gh-issue-158550.cRIHW-.rst

@@ -0,0 +1,2 @@
+Fix incorrect timestamps in Tachyon binary profiles after a sample fails to be
+written.  Patch by Maurycy Pawłowski-Wieronski.

Modules/_remote_debugging/binary_io_writer.c

@@ -950,7 +950,6 @@ process_thread_sample(BinaryWriter *writer, PyObject *thread_info,
 
     /* Calculate timestamp delta */
     uint64_t delta = timestamp_us - entry->prev_timestamp;
-    entry->prev_timestamp = timestamp_us;
 
     /* Process frames and build current stack */
     uint32_t curr_stack[MAX_STACK_DEPTH];
@@ -1006,6 +1005,7 @@ process_thread_sample(BinaryWriter *writer, PyObject *thread_info,
         entry->prev_stack_depth = curr_depth;
     }
 
+    entry->prev_timestamp = timestamp_us;
     writer->total_samples++;
     return 0;
 }