Running Django 3.0 on Python 3.8, using python ./manage.py r

ValueError: signal only works in main thread about djdt-flamegraph HOT 3 CLOSED

jayvdb commented on June 19, 2024

ValueError: signal only works in main thread

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Comments (3)

blopker commented on June 19, 2024

Hello, this issue is discussed in the README.

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jayvdb commented on June 19, 2024

Thanks. python ./manage.py runserver --nothreading --noreload worked. Would be nice if it detected this and de-activated itself. It might even be able to be detected in settings.py to avoid listing it in INSTALLED_APPS.

Now I run into #9

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jayvdb commented on June 19, 2024

I am able to get it to be a bit less problematic with the following; is that worth submitting as-is, maybe with a warning emitted on the console?

 class Sampler(object):
     def __init__(self, interval=0.001):
         self.stack_counts = collections.defaultdict(int)
         self.interval = interval
+        self.disabled = False
 
     def _sample(self, signum, frame):
         stack = []
@@ -87,8 +87,13 @@
         return '\n'.join('%s %d' % (key, value) for key, value in sorted(self.stack_counts.items()))
 
     def start(self):
-        signal.signal(signal.SIGALRM, self._sample)
-        signal.setitimer(signal.ITIMER_REAL, self.interval, self.interval)
+        try:
+            signal.signal(signal.SIGALRM, self._sample)
+            signal.setitimer(signal.ITIMER_REAL, self.interval, self.interval)
+        except ValueError:
+            self.disabled = True
 
     def stop(self):
+        if self.disabled:
+            return
         signal.setitimer(signal.ITIMER_REAL, 0, 0)