I ran into a nasty problem with numpy array: The values of a returned numpy array changed depending if I had an additional print(arr) line or not. While I have solved the issue for me, I am still curious what is actually happening.
Here are a few similar examples. In all cases the output is not what I'd expect. To me the problem looks a bit like a use after free issue, but I might be wrong. In all cases the output was reproducible for me, I didn't get random output.
Example 1
from artiq.experiment import *
import numpy as np
class NumpyTypes1(EnvExperiment):
def build(self):
self.setattr_device("core")
@kernel
def func(self):
if self.core.get_rtio_counter_mu() % 2:
return np.array([30,20,10], dtype=np.int32)
else:
return np.array([10,20,30], dtype=np.int32)
def run(self):
print(self.func())
The (reproducible) output I observe: [ 1 20 1342176984]
Output I'd expect: [30,20,10] or [10,20,30]
The if-branch in the method func is probably required that the compiler does not inline the array. Without the if, the output becomes [10 20 30] (as expected).
Example 2
from artiq.experiment import *
import numpy as np
class NumpyTypes2(EnvExperiment):
def build(self):
self.setattr_device("core")
@kernel
def func(self):
if self.core.get_rtio_counter_mu() % 2:
return np.array([30,20,10], dtype=np.int32)
else:
return np.array([10,20,30], dtype=np.int32)
@kernel
def run(self):
print(self.func())
The (reproducible) output I observe: [1342176948 20 30]
Output I'd expect: [30,20,10] or [10,20,30]
The only difference between NumpyTypes1 and NumpyTypes2 is that run is a kernel method in in NumpyTypes2 but not in NumpyTypes1. It is also curious, that the numbers 1342176984 and 1342176948 are so similar.
Example 3
from artiq.experiment import *
import numpy as np
class NumpyTypes3(EnvExperiment):
def build(self):
self.setattr_device("core")
@kernel
def func(self):
if self.core.get_rtio_counter_mu() % 2:
a = 30
b = 20
c = 10
else:
a = 10
b = 20
c = 30
return np.array([a,b,c], dtype=np.int32)
@kernel
def func2(self):
return self.func()
@kernel
def run(self):
print(self.func())
print(self.func2())
Output:
[10 20 30]
[ 10 1342176880 30]
Expected output:
[10 20 30]
[10 20 30]
func returns the expected array, while func2 does not, even though func2 is just a tiny wrapper. But apparently, it is sufficient that the compiler cannot infer the right types anymore.