Modify resource tracking to write to distinct filenames

doc/releases/changelog-dev.md

@@ -279,6 +279,7 @@ Here's a list of deprecations made this release. For a more detailed breakdown o
 * `null.qubit` can now support an optional `track_resources` argument which allows it to record which gates are executed.
   [(#7226)](https://github.com/PennyLaneAI/pennylane/pull/7226)
   [(#7372)](https://github.com/PennyLaneAI/pennylane/pull/7372)
+  [(#7392)](https://github.com/PennyLaneAI/pennylane/pull/7392)
 
 * A new internal module, `qml.concurrency`, is added to support internal use of multiprocess and multithreaded execution of workloads. This also migrates the use of `concurrent.futures` in `default.qubit` to this new design.
   [(#7303)](https://github.com/PennyLaneAI/pennylane/pull/7303)

pennylane/devices/null_qubit.py

@@ -20,6 +20,7 @@
 import inspect
 import json
 import logging
+import time
 from collections import defaultdict
 from dataclasses import replace
 from functools import lru_cache, singledispatch
@@ -51,6 +52,8 @@
 logger = logging.getLogger(__name__)
 logger.addHandler(logging.NullHandler())
 
+RESOURCES_FNAME_PREFIX = "__pennylane_resources_data_"
+
 
 @singledispatch
 def zero_measurement(
@@ -132,7 +135,7 @@ def _interface(config: ExecutionConfig):
     return config.interface.get_like() if config.gradient_method == "backprop" else "numpy"
 
 
-def _simulate_resource_use(circuit, resources_fname="__pennylane_resources_data.json"):
+def _simulate_resource_use(circuit, outfile):
     num_wires = len(circuit.wires)
     gate_types = defaultdict(int)
 
@@ -163,17 +166,16 @@ def _simulate_resource_use(circuit, resources_fname="__pennylane_resources_data.
             name = f"{controls if controls > 1 else ''}C({name})"
 
         gate_types[name] += 1
-    # NOTE: For now, this information is being printed to match the behavior of catalyst resource tracking.
+    # NOTE: For now, this information is being printed to match the behaviour of catalyst resource tracking.
     #  In the future it may be better to return this information in a more structured way.
-    with open(resources_fname, "w") as f:
-        json.dump(
-            {
-                "num_wires": num_wires,
-                "num_gates": sum(gate_types.values()),
-                "gate_types": gate_types,
-            },
-            f,
-        )
+    json.dump(
+        {
+            "num_wires": num_wires,
+            "num_gates": sum(gate_types.values()),
+            "gate_types": gate_types,
+        },
+        outfile,
+    )
 
 
 @simulator_tracking
@@ -188,7 +190,7 @@ class NullQubit(Device):
             (``['aux_wire', 'q1', 'q2']``). Default ``None`` if not specified.
         shots (int, Sequence[int], Sequence[Union[int, Sequence[int]]]): The default number of shots
             to use in executions involving this device.
-        track_resources (bool): If ``True``, track the number of resources used by the device. This argument is experimental and subject to change.
+        track_resources (bool): If True, track the number of resources used by the device and save them to a JSON file. This argument is experimental and subject to change.
     **Example:**
 
     .. code-block:: python
@@ -285,7 +287,10 @@ def _simulate(self, circuit, interface):
         results = []
 
         if self._track_resources:
-            _simulate_resource_use(circuit)
+            timestamp = int(time.time() * 1e9)  # nanoseconds since epoch
+            resources_fname = f"{RESOURCES_FNAME_PREFIX}{timestamp}.json"
+            with open(resources_fname, "x", encoding="utf-8") as f:
+                _simulate_resource_use(circuit, f)
 
         for s in circuit.shots or [None]:
             r = tuple(

tests/devices/test_null_qubit.py

@@ -67,9 +67,8 @@ def test_resource_tracking_attribute():
     """Test NullQubit track_resources attribute"""
     # pylint: disable=protected-access
     assert NullQubit()._track_resources is False
-    assert NullQubit(track_resources=True)._track_resources is True
-
     dev = NullQubit(track_resources=True)
+    assert dev._track_resources is True
 
     def small_circ(params):
         qml.X(0)
@@ -93,41 +92,59 @@ def small_circ(params):
         qml.RX(params[0], wires=0)
         qml.RX(params[0] * 2, wires=1)
 
+        qml.QubitUnitary([[1, 0], [0, 1]], wires=0)
+        qml.ControlledQubitUnitary([[1, 0], [0, 1]], wires=[0, 1, 2], control_values=[1, 1])
+
         return qml.expval(qml.PauliZ(0))
 
     qnode = qml.QNode(small_circ, dev, diff_method="backprop")
 
     inputs = qml.numpy.array([0.5])
 
+    def check_outputs():
+        written_files = list(
+            filter(
+                lambda fname: fname.startswith(qml.devices.null_qubit.RESOURCES_FNAME_PREFIX),
+                os.listdir(os.getcwd()),
+            )
+        )
+
+        assert len(written_files) == 1
+        resources_fname = written_files[0]
+
+        assert os.path.exists(resources_fname)
+
+        with open(resources_fname, "r", encoding="utf-8") as f:
+            stats = f.read()
+
+        os.remove(resources_fname)
+
+        assert stats == json.dumps(
+            {
+                "num_wires": 3,
+                "num_gates": 11,
+                "gate_types": {
+                    "PauliX": 1,
+                    "Hadamard": 1,
+                    "C(Adj(T))": 1,
+                    "2C(S)": 1,
+                    "CNOT": 1,
+                    "C(IsingXX)": 1,
+                    "Adj(S)": 1,
+                    "RX": 2,
+                    "QubitUnitary": 1,
+                    "ControlledQubitUnitary": 1,
+                },
+            }
+        )
+
+    # Check ordinary forward computation
     qnode(inputs)
+    check_outputs()
 
-    # Check that resource tracking doesn't interfere with backprop
+    # Check backpropagation
     assert qml.grad(qnode)(inputs) == 0
-
-    RESOURCES_FNAME = "__pennylane_resources_data.json"
-    assert os.path.exists(RESOURCES_FNAME)
-
-    with open(RESOURCES_FNAME, "r") as f:
-        stats = f.read()
-
-    os.remove(RESOURCES_FNAME)
-
-    assert stats == json.dumps(
-        {
-            "num_wires": 3,
-            "num_gates": 9,
-            "gate_types": {
-                "PauliX": 1,
-                "Hadamard": 1,
-                "C(Adj(T))": 1,
-                "2C(S)": 1,
-                "CNOT": 1,
-                "C(IsingXX)": 1,
-                "Adj(S)": 1,
-                "RX": 2,
-            },
-        }
-    )
+    check_outputs()
 
 
 @pytest.mark.parametrize("shots", (None, 10))