Refactor parallelism utilities for public API

.azure/test-linux.yml

@@ -122,6 +122,7 @@ jobs:
           popd
         env:
           QISKIT_PARALLEL: FALSE
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
           RUST_BACKTRACE: 1
         displayName: 'Run Python tests'
 

.azure/test-macos.yml

@@ -65,6 +65,7 @@ jobs:
           stestr run
         env:
           QISKIT_PARALLEL: FALSE
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
           RUST_BACKTRACE: 1
         displayName: "Run tests"
 

.azure/test-windows.yml

@@ -68,6 +68,7 @@ jobs:
           LANG: 'C.UTF-8'
           PYTHONIOENCODING: 'utf-8:backslashreplace'
           QISKIT_PARALLEL: FALSE
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
           RUST_BACKTRACE: 1
         displayName: 'Run tests'
 

.github/workflows/coverage.yml

@@ -61,6 +61,7 @@ jobs:
         env:
           QISKIT_TEST_CAPTURE_STREAMS: 1
           QISKIT_PARALLEL: FALSE
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
           PYTHON: "coverage run --source qiskit --parallel-mode"
 
       - name: Convert to lcov and combine data

.github/workflows/qpy.yml

@@ -37,3 +37,5 @@ jobs:
       - name: Run QPY backwards compatibility tests
         working-directory: test/qpy_compat
         run: ./run_tests.sh
+        env:
+          QISKIT_IGNORE_USER_SETTINGS: TRUE

.github/workflows/randomized_tests.yml

@@ -28,6 +28,7 @@ jobs:
         run: make test_randomized
         env:
           RUST_BACKTRACE: 1
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
       - name: Create comment on failed test run
         if: ${{ failure() }}
         uses: peter-evans/create-or-update-comment@v4

.github/workflows/slow.yml

@@ -26,6 +26,7 @@ jobs:
         env:
           RUST_BACKTRACE: 1
           QISKIT_TESTS: "run_slow"
+          QISKIT_IGNORE_USER_SETTINGS: TRUE
       - name: Create comment on failed test run
         if: ${{ failure() }}
         uses: peter-evans/create-or-update-comment@v4

.github/workflows/tests.yml

@@ -52,3 +52,6 @@ jobs:
         if: matrix.python-version == '3.10'
       - name: 'Run tests'
         run: stestr run
+        env:
+          QISKIT_PARALLEL: FALSE
+          QISKIT_IGNORE_USER_SETTINGS: TRUE

qiskit/circuit/quantumcircuit.py

@@ -19,7 +19,7 @@
 import collections.abc
 import copy as _copy
 import itertools
-import multiprocessing as mp
+import multiprocessing
 import typing
 from collections import OrderedDict, defaultdict, namedtuple
 from typing import (
@@ -41,7 +41,6 @@
 from qiskit._accelerate.circuit import CircuitData
 from qiskit._accelerate.circuit import StandardGate
 from qiskit.exceptions import QiskitError
-from qiskit.utils.multiprocessing import is_main_process
 from qiskit.circuit.instruction import Instruction
 from qiskit.circuit.gate import Gate
 from qiskit.circuit.parameter import Parameter
@@ -1498,11 +1497,10 @@ def _cls_prefix(cls) -> str:
 
     def _name_update(self) -> None:
         """update name of instance using instance number"""
-        if not is_main_process():
-            pid_name = f"-{mp.current_process().pid}"
-        else:
+        if multiprocessing.parent_process() is None:
             pid_name = ""
-
+        else:
+            pid_name = f"-{multiprocessing.current_process().pid}"
         self.name = f"{self._base_name}-{self._cls_instances()}{pid_name}"
 
     def has_register(self, register: Register) -> bool:

qiskit/pulse/schedule.py

@@ -52,7 +52,6 @@
 from qiskit.pulse.instructions import Instruction, Reference
 from qiskit.pulse.utils import instruction_duration_validation
 from qiskit.pulse.reference_manager import ReferenceManager
-from qiskit.utils.multiprocessing import is_main_process
 from qiskit.utils import deprecate_arg
 from qiskit.utils.deprecate_pulse import deprecate_pulse_func
 
@@ -146,7 +145,7 @@ def __init__(
 
         if name is None:
             name = self.prefix + str(next(self.instances_counter))
-            if sys.platform != "win32" and not is_main_process():
+            if sys.platform != "win32" and mp.parent_process() is not None:
                 name += f"-{mp.current_process().pid}"
 
         self._name = name
@@ -1007,7 +1006,7 @@ def __init__(
 
         if name is None:
             name = self.prefix + str(next(self.instances_counter))
-            if sys.platform != "win32" and not is_main_process():
+            if sys.platform != "win32" and mp.parent_process() is not None:
                 name += f"-{mp.current_process().pid}"
 
         # This points to the parent schedule object in the current scope.

qiskit/transpiler/passes/layout/sabre_layout.py

@@ -39,7 +39,7 @@
 from qiskit.transpiler.passes.routing.sabre_swap import _build_sabre_dag, _apply_sabre_result
 from qiskit.transpiler.target import Target
 from qiskit.transpiler.coupling import CouplingMap
-from qiskit.utils.parallel import CPU_COUNT
+from qiskit.utils import default_num_processes
 
 logger = logging.getLogger(__name__)
 
@@ -174,11 +174,11 @@ def __init__(
         self.max_iterations = max_iterations
         self.trials = swap_trials
         if swap_trials is None:
-            self.swap_trials = CPU_COUNT
+            self.swap_trials = default_num_processes()
         else:
             self.swap_trials = swap_trials
         if layout_trials is None:
-            self.layout_trials = CPU_COUNT
+            self.layout_trials = default_num_processes()
         else:
             self.layout_trials = layout_trials
         self.skip_routing = skip_routing

qiskit/transpiler/passes/routing/sabre_swap.py

@@ -29,7 +29,7 @@
 from qiskit.transpiler.target import Target
 from qiskit.transpiler.passes.layout import disjoint_utils
 from qiskit.dagcircuit import DAGCircuit, DAGOpNode
-from qiskit.utils.parallel import CPU_COUNT
+from qiskit.utils import default_num_processes
 
 from qiskit._accelerate.sabre import sabre_routing, Heuristic, SetScaling, NeighborTable, SabreDAG
 from qiskit._accelerate.nlayout import NLayout
@@ -167,7 +167,7 @@ def __init__(self, coupling_map, heuristic="basic", seed=None, fake_run=False, t
         self.heuristic = heuristic
         self.seed = seed
         if trials is None:
-            self.trials = CPU_COUNT
+            self.trials = default_num_processes()
         else:
             self.trials = trials
 

qiskit/transpiler/preset_passmanagers/builtin_plugins.py

@@ -67,7 +67,7 @@
     SXGate,
     SXdgGate,
 )
-from qiskit.utils.parallel import CPU_COUNT
+from qiskit.utils import default_num_processes
 from qiskit import user_config
 
 CONFIG = user_config.get_config()
@@ -1029,5 +1029,5 @@ def _swap_mapped(property_set):
 
 def _get_trial_count(default_trials=5):
     if CONFIG.get("sabre_all_threads", None) or os.getenv("QISKIT_SABRE_ALL_THREADS"):
-        return max(CPU_COUNT, default_trials)
+        return max(default_num_processes(), default_trials)
     return default_trials

qiskit/user_config.py

@@ -245,15 +245,19 @@ def set_config(key, value, section=None, file_path=None):
 
 
 def get_config():
-    """Read the config file from the default location or env var
+    """Read the config file from the default location or env var.
 
-    It will read a config file at either the default location
-    ~/.qiskit/settings.conf or if set the value of the QISKIT_SETTINGS env var.
+    It will read a config file at the location specified by the ``QISKIT_SETTINGS`` environment
+    variable if set, or ``$HOME/.qiskit/settings.conf`` if not.
+
+    If the environment variable ``QISKIT_IGNORE_USER_SETTINGS`` is set to the string ``TRUE``, this
+    will return an empty configuration, regardless of all other variables.
 
-    It will return the parsed settings dict from the parsed config file.
     Returns:
         dict: The settings dict from the parsed config file.
     """
+    if os.getenv("QISKIT_IGNORE_USER_SETTINGS", "false").lower() == "true":
+        return {}
     filename = os.getenv("QISKIT_SETTINGS", DEFAULT_FILENAME)
     if not os.path.isfile(filename):
         return {}

qiskit/utils/__init__.py

@@ -41,8 +41,10 @@
 Multiprocessing
 ===============
 
-.. autofunction:: local_hardware_info
+.. autofunction:: default_num_processes
 .. autofunction:: is_main_process
+.. autofunction:: local_hardware_info
+.. autofunction:: should_run_in_parallel
 
 A helper function for calling a custom function with Python
 :class:`~concurrent.futures.ProcessPoolExecutor`. Tasks can be executed in parallel using this function.
@@ -62,28 +64,33 @@
     deprecate_func,
     deprecate_function,
 )
-from .multiprocessing import local_hardware_info
-from .multiprocessing import is_main_process
 from .units import apply_prefix, detach_prefix
 from .classtools import wrap_method
 from .lazy_tester import LazyDependencyManager, LazyImportTester, LazySubprocessTester
 
 from . import optionals
 
-from .parallel import parallel_map, should_run_in_parallel
+from .parallel import (
+    parallel_map,
+    should_run_in_parallel,
+    local_hardware_info,
+    is_main_process,
+    default_num_processes,
+)
 
 __all__ = [
     "LazyDependencyManager",
     "LazyImportTester",
     "LazySubprocessTester",
     "add_deprecation_to_docstring",
+    "apply_prefix",
+    "default_num_processes",
     "deprecate_arg",
     "deprecate_arguments",
     "deprecate_func",
     "deprecate_function",
-    "local_hardware_info",
     "is_main_process",
-    "apply_prefix",
+    "local_hardware_info",
     "parallel_map",
     "should_run_in_parallel",
 ]