From f2e24e49829360af4381cb0ffc46f62e343054fa Mon Sep 17 00:00:00 2001
From: Kevin Tian <kevin.tian@ibm.com>
Date: Wed, 6 Dec 2023 10:28:13 -0500
Subject: [PATCH] Don't block for the first job in a session (#1170)

* don't block if backend not selected

* add reno

* add test
---
 qiskit_ibm_runtime/session.py                       |  6 +++++-
 .../backend-blocking-job-70ebcf44855cbdfd.yaml      |  8 ++++++++
 test/integration/test_session.py                    | 13 +++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 releasenotes/notes/backend-blocking-job-70ebcf44855cbdfd.yaml

diff --git a/qiskit_ibm_runtime/session.py b/qiskit_ibm_runtime/session.py
index 7b9905ac7..58b6eaa08 100644
--- a/qiskit_ibm_runtime/session.py
+++ b/qiskit_ibm_runtime/session.py
@@ -23,6 +23,7 @@
 from .runtime_job import RuntimeJob
 from .utils.result_decoder import ResultDecoder
 from .ibm_backend import IBMBackend
+from .exceptions import RuntimeJobTimeoutError
 from .utils.default_session import set_cm_session
 from .utils.deprecation import deprecate_arguments
 
@@ -180,7 +181,10 @@ def run(
                 self._setup_lock.release()
 
         if self._backend is None:
-            self._backend = job.backend().name
+            try:
+                self._backend = job.backend(0).name
+            except RuntimeJobTimeoutError:
+                self._backend = None
 
         return job
 
diff --git a/releasenotes/notes/backend-blocking-job-70ebcf44855cbdfd.yaml b/releasenotes/notes/backend-blocking-job-70ebcf44855cbdfd.yaml
new file mode 100644
index 000000000..c9cf202fb
--- /dev/null
+++ b/releasenotes/notes/backend-blocking-job-70ebcf44855cbdfd.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixed an issue where the first job in a cloud channel session without a backend passed 
+    in would block other jobs from starting. This would happen because the first job would
+    attempt to retrieve the backend from the job which required the job to be in a 
+    completed state. 
+
diff --git a/test/integration/test_session.py b/test/integration/test_session.py
index b8c086a59..4af012f8a 100644
--- a/test/integration/test_session.py
+++ b/test/integration/test_session.py
@@ -101,6 +101,19 @@ def test_session_from_id(self, service):
         job = sampler.run(ReferenceCircuits.bell(), shots=400)
         self.assertEqual(session_id, job.session_id)
 
+    @run_integration_test
+    def test_session_no_backend(self, service):
+        """Test session without passing in backend."""
+        if self.dependencies.channel == "ibm_quantum":
+            self.skipTest("Not supported on ibm_quantum")
+        with Session(service) as session:
+            sampler = Sampler(session=session)
+            job1 = sampler.run(ReferenceCircuits.bell(), shots=400)
+            job2 = sampler.run(ReferenceCircuits.bell(), shots=400)
+        self.assertTrue(job1.backend())
+        self.assertTrue(job2.backend())
+        self.assertEqual(job1.backend().name, job2.backend().name)
+
 
 class TestBackendRunInSession(IBMIntegrationTestCase):
     """Integration tests for Backend.run in Session."""