Fix Channel.__hash__ in multiprocessing contexts (backport #11251)

qiskit/pulse/channels.py

@@ -96,7 +96,6 @@ def __init__(self, index: int):
         """
         self._validate_index(index)
         self._index = index
-        self._hash = hash((self.__class__.__name__, self._index))
 
     @property
     def index(self) -> Union[int, ParameterExpression]:
@@ -156,7 +155,7 @@ def __eq__(self, other: "Channel") -> bool:
         return type(self) is type(other) and self._index == other._index
 
     def __hash__(self):
-        return self._hash
+        return hash((type(self), self._index))
 
 
 class PulseChannel(Channel, metaclass=ABCMeta):

qiskit/pulse/instructions/instruction.py

@@ -53,7 +53,6 @@ def __init__(
         """
         self._operands = operands
         self._name = name
-        self._hash = None
         self._validate()
 
     def _validate(self):
@@ -301,9 +300,7 @@ def __eq__(self, other: "Instruction") -> bool:
         return isinstance(other, type(self)) and self.operands == other.operands
 
     def __hash__(self) -> int:
-        if self._hash is None:
-            self._hash = hash((type(self), self.operands, self.name))
-        return self._hash
+        return hash((type(self), self.operands, self.name))
 
     def __add__(self, other):
         """Return a new schedule with `other` inserted within `self` at `start_time`.

releasenotes/notes/fix-pulse-channel-hash-549a8fb5d8738c4d.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixed the :func:`hash` of Qiskit Pulse ``Channel`` objects (such as :class:`.DriveChannel`) in
+    cases where the channel was transferred from one Python process to another that used a different
+    hash seed.