From 360960461e5141a49cc8b4c8fdc7ab8265c6547d Mon Sep 17 00:00:00 2001
From: David Berenstein <david.m.berenstein@gmail.com>
Date: Wed, 12 Aug 2026 23:30:54 +0200
Subject: [PATCH] fix: resume the scheduler in stop_task only if start_task
 paused it

start_task stops the periodic scheduler but nothing ever restarted it, so a
tracker started with start() lost its periodic measurements after the first
task. Restarting it unconditionally would instead leave a 1s scheduler
running for pure start_task/stop_task users, so track whether start_task
actually paused a running scheduler.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 codecarbon/emissions_tracker.py |  9 +++++++++
 tests/test_emissions_tracker.py | 26 ++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/codecarbon/emissions_tracker.py b/codecarbon/emissions_tracker.py
index 96ed00c91..ead914a24 100644
--- a/codecarbon/emissions_tracker.py
+++ b/codecarbon/emissions_tracker.py
@@ -296,6 +296,7 @@ def _initialize_runtime_state(self) -> None:
         self._tasks: Dict[str, Task] = {}
         self._active_task: Optional[str] = None
         self._active_task_emissions_at_start: Optional[EmissionsData] = None
+        self._scheduler_paused_by_task = False
         self._hardware = []
         self._hardware_initialized = False
 
@@ -752,6 +753,10 @@ def start_task(self, task_name=None) -> None:
 
         # Stop scheduler as we do not want it to interfere with the task measurement
         if self._scheduler:
+            # Only resume it in stop_task if it was actually running, i.e. the tracker
+            # was started with start(). Pure start_task/stop_task usage must not leave
+            # a periodic measurement running behind.
+            self._scheduler_paused_by_task = not self._scheduler._stopped
             self._scheduler.stop()
 
         # Task background thread for measuring power
@@ -848,6 +853,10 @@ def stop_task(self, task_name: str = None) -> EmissionsData:
         self._active_task = None
         self._active_task_emissions_at_start = None  # Clear task-specific start data
 
+        if self._scheduler is not None and self._scheduler_paused_by_task:
+            self._scheduler_paused_by_task = False
+            self._scheduler.start()
+
         return task_emission_data
 
     @suppress(Exception)
diff --git a/tests/test_emissions_tracker.py b/tests/test_emissions_tracker.py
index 8ab12e5d8..f5699b510 100644
--- a/tests/test_emissions_tracker.py
+++ b/tests/test_emissions_tracker.py
@@ -765,6 +765,32 @@ def test_start_task_returns_when_engine_initialization_fails(
             any("Tracker not initialized" in message for message in logs.output)
         )
 
+    def test_stop_task_resumes_scheduler_only_if_start_task_paused_it(
+        self,
+        mock_cli_setup,
+        mock_log_values,
+        mocked_get_gpu_details,
+        mocked_env_cloud_details,
+        mocked_get_gpu_utilization_list,
+        mocked_is_gpu_details_available,
+        mocked_is_nvidia_system,
+    ):
+        # Pure start_task/stop_task usage: no periodic scheduler must be left running.
+        tracker = EmissionsTracker(save_to_file=False)
+        tracker.start_task("task-only")
+        tracker.stop_task()
+        self.assertTrue(tracker._scheduler._stopped)
+        tracker.stop()
+
+        # start() then start_task/stop_task: the paused scheduler must be resumed.
+        tracker = EmissionsTracker(save_to_file=False)
+        tracker.start()
+        tracker.start_task("task-in-run")
+        self.assertTrue(tracker._scheduler._stopped)
+        tracker.stop_task()
+        self.assertFalse(tracker._scheduler._stopped)
+        tracker.stop()
+
     @mock.patch("codecarbon.external.ram.RAM.measure_power_and_energy")
     @mock.patch("codecarbon.external.hardware.CPU.measure_power_and_energy")
     @mock.patch(