Adds state to the tracker and raises exceptions if starting / stoppin…

…g in the wrong state

src/gpu_tracker/tracker.py

@@ -10,10 +10,15 @@
 import psutil
 import subprocess as subp
 import logging as log
+import enum
 import sys
 
 
 class Tracker:
+    class State(enum.Enum):
+        NEW = 0
+        STARTED = 1
+        STOPPED = 2
     """
     Runs a thread in the background that tracks the compute time, maximum RAM, and maximum GPU RAM usage within a context manager or explicit ``start()`` and ``stop()`` methods.
     Calculated quantities are scaled depending on the units chosen for them (e.g. megabytes vs. gigabytes, hours vs. days, etc.).
@@ -78,6 +83,10 @@ def __init__(
         self.max_gpu_ram = MaxGPURAM(unit=gpu_ram_unit, system_capacity=self._system_gpu_ram(measurement='total'))
         self.cpu_utilization = CPUUtilization(system_core_count=psutil.cpu_count())
         self.compute_time = ComputeTime(unit=time_unit)
+        self.state = Tracker.State.NEW
+
+    def __repr__(self):
+        return (f'State: {self.state.name}')
 
     def _log_warning(self, warning: str):
         if not self.disable_logs:
@@ -228,10 +237,19 @@ def _profile(self):
                 print(error)
 
     def __enter__(self) -> Tracker:
+        if self.state == Tracker.State.STARTED:
+            raise RuntimeError('Cannot start tracking when tracking has already started.')
+        elif self.state == Tracker.State.STOPPED:
+            raise RuntimeError('Cannot start tracking when tracking has already stopped.')
+        self.state = Tracker.State.STARTED
         self._thread.start()
         return self
 
     def __exit__(self, *_):
+        if self.state == Tracker.State.NEW:
+            raise RuntimeError('Cannot stop tracking when tracking has not started yet.')
+        if self.state == Tracker.State.STOPPED:
+            raise RuntimeError('Cannot stop tracking when tracking has already stopped.')
         n_join_attempts = 0
         while n_join_attempts < self.n_join_attempts:
             self._stop_event.set()
@@ -248,6 +266,7 @@ def __exit__(self, *_):
             if self.kill_if_join_fails:
                 log.warning('The thread failed to join and kill_if_join_fails is set. Exiting ...')
                 sys.exit(1)
+        self.state = Tracker.State.STOPPED
 
     def start(self):
         """

tests/test_tracker.py

@@ -219,3 +219,28 @@ def test_validate_unit():
     with pt.raises(ValueError) as error:
         gput.Tracker(ram_unit='milibytes')
     assert str(error.value) == '"milibytes" is not a valid memory unit. Valid values are bytes, gigabytes, kilobytes, megabytes, terabytes'
+
+
+def test_state(mocker):
+    profile_mock = mocker.patch('gpu_tracker.tracker.Tracker._profile')
+    assert not profile_mock.called
+    mocker.patch('gpu_tracker.tracker.subp.check_output', side_effect=[b''])
+    tracker = gput.Tracker()
+    assert tracker.__repr__() == 'State: NEW'
+    with pt.raises(RuntimeError) as error:
+        tracker.stop()
+    assert str(error.value) == 'Cannot stop tracking when tracking has not started yet.'
+    tracker.start()
+    assert tracker.__repr__() == 'State: STARTED'
+    with pt.raises(RuntimeError) as error:
+        tracker.start()
+    assert str(error.value) == 'Cannot start tracking when tracking has already started.'
+    tracker.stop()
+    assert tracker.__repr__() == 'State: STOPPED'
+    with pt.raises(RuntimeError) as error:
+        tracker.start()
+    assert str(error.value) == 'Cannot start tracking when tracking has already stopped.'
+    with pt.raises(RuntimeError) as error:
+        tracker.stop()
+    assert str(error.value) == 'Cannot stop tracking when tracking has already stopped.'
+    assert profile_mock.called