Segmentation fault when the number of iterations is 0

[koffie]

We ran the complete testsuite of qxbackend with qxecelarator 0.6.2 and one testcase caused qxelarator to produce a segmentation fault. A minimal example to reproduce this is the following:

from qxelarator import QX
qx = QX()
qx.set_string("""version 1.0
qubits 2
.test
    h q[1]
""")
result_raw = qx.execute(0)

Running this gives:

Number of runs is 0
Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

It would be nice if an actual python error was raised instead of a segmentation fault.

I.e. if one runs:

result_raw = qx.execute(-1)

instead one does get an error that can be caught by python and handled appriopriately

Traceback (most recent call last):
  File "/code/qutech/qx-backend/.venv/lib/python3.9/site-packages/IPython/core/interactiveshell.py", line 3442, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-3-9078becc5ff9>", line 9, in <module>
    result_raw = qx.execute(-1)
  File "/code/qutech/qx-backend/.venv/lib/python3.9/site-packages/qxelarator/qxelarator.py", line 77, in execute
    return _qxelarator.QX_execute(self, iterations)
OverflowError: in method 'QX_execute', argument 2 of type 'std::size_t'

It would be nice if a similar OverflowError, or an ValueError ccould be raised when the number of iterations is 0.

[pablolh]

A very legit issue, I'll work on it asap. Thanks for reporting!

[koffie]

Actually I found another way to expose uncaught errors in the underlying c++ that are not nicely wrapped in python code so that they can be dealt with.

Example:

from qxelarator import QX
qx.execute(1)

output:

No circuit successfully loaded, call set(...) first
libc++abi: terminating with uncaught exception of type std::bad_alloc: std::bad_alloc
Process finished with exit code 134 (interrupted by signal 6: SIGABRT)

Note that the above code for some reason seems to produce different errors when executed multiple times. I've seen SIGABRT, SIGBUS and SIGSEGV. They are probably being caused by the same underlying issue.

I've not been able to create any such uncaught exceptions using qxelarator.execute_string, so good job on this new interface.

[arcturusannamalai]

I wonder if this issue is resolved on latest main branch