[service] Add a base class for the connection pool.

Add a base class for the ServiceConnectionPool that provides the same
interface but does no caching.

compiler_gym/envs/compiler_env.py

@@ -30,7 +30,10 @@
     ServiceTransportError,
     SessionNotFound,
 )
-from compiler_gym.service.connection_pool import ServiceConnectionPool
+from compiler_gym.service.connection_pool import (
+    ServiceConnectionPool,
+    ServiceConnectionPoolBase,
+)
 from compiler_gym.service.proto import AddBenchmarkRequest
 from compiler_gym.service.proto import Benchmark as BenchmarkProto
 from compiler_gym.service.proto import (
@@ -165,7 +168,7 @@ def __init__(
         derived_observation_spaces: Optional[List[Dict[str, Any]]] = None,
         connection_settings: Optional[ConnectionOpts] = None,
         service_connection: Optional[CompilerGymServiceConnection] = None,
-        service_pool: Optional[ServiceConnectionPool] = None,
+        service_pool: Optional[ServiceConnectionPoolBase] = None,
         logger: Optional[logging.Logger] = None,
     ):
         """Construct and initialize a CompilerGym environment.
@@ -250,15 +253,15 @@ def __init__(
         self._connection_settings = connection_settings or ConnectionOpts()
 
         if service_connection is None:
-            self._service_pool: Optional[ServiceConnectionPool] = (
+            self._service_pool: Optional[ServiceConnectionPoolBase] = (
                 ServiceConnectionPool.get() if service_pool is None else service_pool
             )
             self.service = self._service_pool.acquire(
                 endpoint=self._service_endpoint,
                 opts=self._connection_settings,
             )
         else:
-            self._service_pool: Optional[ServiceConnectionPool] = service_pool
+            self._service_pool: Optional[ServiceConnectionPoolBase] = service_pool
             self.service = service_connection
 
         self.datasets = Datasets(datasets or [])

compiler_gym/service/connection_pool.py

@@ -18,7 +18,21 @@
 ServiceConnectionCacheKey = Tuple[Path, ConnectionOpts]
 
 
-class ServiceConnectionPool:
+class ServiceConnectionPoolBase:
+    """A class that provides the base interface for service connection pools."""
+
+    def acquire(
+        self, endpoint: Path, opts: ConnectionOpts
+    ) -> CompilerGymServiceConnection:
+        return CompilerGymServiceConnection(
+            endpoint=endpoint, opts=opts, owning_service_pool=self
+        )
+
+    def release(self, service: CompilerGymServiceConnection) -> None:
+        pass
+
+
+class ServiceConnectionPool(ServiceConnectionPoolBase):
     """An object pool for compiler service connections.
 
     This class implements a thread-safe pool for compiler service connections.
@@ -52,7 +66,7 @@ class ServiceConnectionPool:
     :vartype allocated: Set[CompilerGymServiceConnection]
     """
 
-    def __init__(self) -> None:
+    def __init__(self):
         """"""
         self._lock = Lock()
         self.pool: Dict[