Cannot run qrack on platform without `OpenCL`

[yorgossot]

While trying to run qrack on a device without OpenCL (and without a GPU as it is on the cloud), this error shows up.

Note that the flag isOpenCL was set to False while initializing the qrack device.

Is this expected? Is it possible to use qrack with this setup?

IMPORTANT: Did you remember to install OpenCL, if your Qrack version was built with OpenCL?
---------------------------------------------------------------------------
OSError                                   Traceback (most recent call last)
File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_system/qrack_system.py:36, in QrackSystem.__init__(self)
     35 try:
---> 36     self.qrack_lib = CDLL(shared_lib_path)
     37 except Exception as e:

File ~/miniconda3/envs/qrack_env/lib/python3.10/ctypes/__init__.py:374, in CDLL.__init__(self, name, mode, handle, use_errno, use_last_error, winmode)
    373 if handle is None:
--> 374     self._handle = _dlopen(self._name, mode)
    375 else:

OSError: libOpenCL.so.1: cannot open shared object file: No such file or directory

During handling of the above exception, another exception occurred:

OSError                                   Traceback (most recent call last)
File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_system/qrack_system.py:46, in QrackSystem.__init__(self)
     45 try:
---> 46     self.qrack_lib = CDLL(shared_lib_path)
     47 except Exception as e:

File ~/miniconda3/envs/qrack_env/lib/python3.10/ctypes/__init__.py:374, in CDLL.__init__(self, name, mode, handle, use_errno, use_last_error, winmode)
    373 if handle is None:
--> 374     self._handle = _dlopen(self._name, mode)
    375 else:

OSError: /usr/local/lib/qrack/libqrack_pinvoke.so: cannot open shared object file: No such file or directory

During handling of the above exception, another exception occurred:

OSError                                   Traceback (most recent call last)
Cell In[2], line 3
      1 import pennylane as qml
----> 3 dev = qml.device("qrack.simulator", wires=1, shots=1, noise=0.5, isTensorNetwork=False, isStabilizerHybrid=True, isOpenCL=False)

File ~/miniconda3/envs/qrack_env/lib/python3.10/site-packages/pennylane/devices/device_constructor.py:246, in device(name, *args, **kwargs)
    243 options.update(kwargs)
    245 # loads the device class
--> 246 plugin_device_class = plugin_devices[name].load()
    248 def _safe_specifier_set(version_str):
    249     """Safely create a SpecifierSet from a version string."""

File ~/miniconda3/envs/qrack_env/lib/python3.10/importlib/metadata/__init__.py:171, in EntryPoint.load(self)
    166 """Load the entry point from its definition. If only a module
    167 is indicated by the value, return that module. Otherwise,
    168 return the named object.
    169 """
    170 match = self.pattern.match(self.value)
--> 171 module = import_module(match.group('module'))
    172 attrs = filter(None, (match.group('attr') or '').split('.'))
    173 return functools.reduce(getattr, attrs, module)

File ~/miniconda3/envs/qrack_env/lib/python3.10/importlib/__init__.py:126, in import_module(name, package)
    124             break
    125         level += 1
--> 126 return _bootstrap._gcd_import(name[level:], package, level)

File <frozen importlib._bootstrap>:1050, in _gcd_import(name, package, level)

File <frozen importlib._bootstrap>:1027, in _find_and_load(name, import_)

File <frozen importlib._bootstrap>:1006, in _find_and_load_unlocked(name, import_)

File <frozen importlib._bootstrap>:688, in _load_unlocked(spec)

File <frozen importlib._bootstrap_external>:883, in exec_module(self, module)

File <frozen importlib._bootstrap>:241, in _call_with_frames_removed(f, *args, **kwds)

File ~/miniconda3/envs/qrack_env/lib/python3.10/site-packages/pennylane_qrack/qrack_device.py:36
     28 from pennylane.ops import (
     29     StatePrep,
     30     BasisState,
     31     QubitUnitary,
     32     Adjoint,
     33 )
     34 from pennylane.wires import Wires
---> 36 from pyqrack import QrackSimulator, Pauli
     38 from ._version import __version__
     39 from sys import platform as _platform

File ~/.local/lib/python3.10/site-packages/pyqrack/__init__.py:9
      7 from .neuron_activation_fn import NeuronActivationFn
      8 from .quimb_circuit_type import QuimbCircuitType
----> 9 from .qrack_circuit import QrackCircuit
     10 from .qrack_neuron import QrackNeuron
     11 from .qrack_neuron_torch_layer import QrackTorchNeuron, QrackNeuronFunction, QrackNeuronTorchLayer

File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_circuit.py:8
      1 # (C) Daniel Strano and the Qrack contributors 2017-2025. All rights reserved.
      2 #
      3 # Use of this source code is governed by an MIT-style license that can be
      4 # found in the LICENSE file or at https://opensource.org/licenses/MIT.
      6 import ctypes
----> 8 from .qrack_system import Qrack
      9 from .quimb_circuit_type import QuimbCircuitType
     11 _IS_QISKIT_AVAILABLE = True

File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_system/__init__.py:9
      6 from .qrack_system import QrackSystem
      8 # Global entry-point for Qrack shared library
----> 9 Qrack = QrackSystem()

File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_system/qrack_system.py:59, in QrackSystem.__init__(self)
     57         except Exception as e:
     58             print("IMPORTANT: Did you remember to install OpenCL, if your Qrack version was built with OpenCL?")
---> 59             raise e
     61 self.fppow = 5
     62 if "QRACK_FPPOW" in os.environ:

File ~/.local/lib/python3.10/site-packages/pyqrack/qrack_system/qrack_system.py:56, in QrackSystem.__init__(self)
     53     shared_lib_path = "/usr/lib/qrack/libqrack_pinvoke.so"
     55 try:
---> 56     self.qrack_lib = CDLL(shared_lib_path)
     57 except Exception as e:
     58     print("IMPORTANT: Did you remember to install OpenCL, if your Qrack version was built with OpenCL?")

File ~/miniconda3/envs/qrack_env/lib/python3.10/ctypes/__init__.py:374, in CDLL.__init__(self, name, mode, handle, use_errno, use_last_error, winmode)
    371 self._FuncPtr = _FuncPtr
    373 if handle is None:
--> 374     self._handle = _dlopen(self._name, mode)
    375 else:
    376     self._handle = handle

OSError: /usr/lib/qrack/libqrack_pinvoke.so: cannot open shared object file: No such file or directory

@dime10
@WrathfulSpatula
@Swastikmajumdar10

[WrathfulSpatula]

The problem is that because Qrack is built with OpenCL, you still need libopencl.so on the system. Install libopencl.so with an appropriate package manager. Alternatively, pyqrack offers a package variant called pyqrack-cpu that is built without OpenCL. If it's really a problem to install libopencl.so on your system, I could package pennylane-qrack-cpu, and you could use that. Just let me know.

[WrathfulSpatula]

By the way, there are a couple of other things worth pointing out: if you're on Mac, you're using a deprecated OS and wheel. With that said, I would love to continue to support you with updates! The only problem is that I don't have a Mac 13 system on which to build an updated wheel. You could do us a tremendous favor by building a wheel locally, to get the latest code updates, and passing us the wheel artifact. However, further, while you might not have a discrete GPU on the system, you likely do have an integrated graphics. Qrack with OpenCL likely supports acceleration on it! This will tend to be faster than pure CPU simulation, anyway! (I use the Intel HD all the time, which is basically the same as the Intel Iris, on Intel Mac systems.) You have lots of options! However, because GitHub has decommissioned Mac 13 runners, I can't build an updated wheel for you.

[Swastikmajumdar10]

Thank you for the quick response! @WrathfulSpatula
We have tried installing libopencl.so previously on our system Ubuntu 22.04.5 LTS but we have been running into trouble, would it be possible for you to provide us with the pennylane-qrack-cpu package, thank you!

[dime10]

Speaking of the pyqrack-cpu package, I tried installing it on two different systems, but none of them worked. Then I realized that it only installed the source package both times, which is not functional (at least by itself). Just thought it might be useful to know that this could be very confusing for users since they'll see seemingly unrelated errors later after thinking they installed the package successfully.

[WrathfulSpatula]

@dime10 Pretty much by definition, the source package can't know your CPU architecture and OS. Hence, we note in the (very short) PyQrack README that the source package also requires that Qrack is installed from source, separately. We could package it like pyqrack-cuda, which is only distributed as source and pulls in the Qrack repository to build during installation (because CUDA architecture must be known at compile time, hence our options are either to follow forced CUDA architecture generation "deprecation" every couple of years, or build from source locally every time), which I don't like, because this is a much heavier-weight installation process. I'll consider it, though.

Yes, I'll go ahead and create a pennylane-qrack-cpu package. Fair enough.

[WrathfulSpatula]

You should be good-to-go: https://pypi.org/project/pennylane-qrack-cpu/

If a wheel isn't available for the CPU-only version, but it is for pennylane-qrack, then note that the original wheel is already CPU-only (specifically for Macs).

This is a drop-in replacement: just update your dependencies to point this package version, but no code changes are necessary.

Please let me know if it doesn't work, or if you run into any problems.

[dime10]

Thanks for providing the new package Dan!

Hence, we note in the (very short) PyQrack README that the source package also requires that Qrack is installed from source, separately.

Fair enough, I was just thinking it might not be obvious to the user that they got stuck with a source-only package. Just thought I'd mention it.