[gcc] Disable service connection pool for GCC.

Issue facebookresearch#583.

compiler_gym/envs/gcc/gcc_env.py

@@ -16,6 +16,7 @@
 from compiler_gym.envs.gcc.gcc_rewards import AsmSizeReward, ObjSizeReward
 from compiler_gym.service import ConnectionOpts
 from compiler_gym.service.client_service_compiler_env import ClientServiceCompilerEnv
+from compiler_gym.service.connection_pool import ServiceConnectionPoolBase
 from compiler_gym.util.decorators import memoized_property
 from compiler_gym.util.gym_type_hints import ObservationType
 from compiler_gym.util.gym_type_hints import OptionalArgumentValue
@@ -78,6 +79,13 @@ def __init__(
         #    initialization may time out.
         Gcc(bin=gcc_bin)
 
+        # NOTE(github.com/facebookresearch/CompilerGym/pull/583): The GCC
+        # environment stalls on the StartSession() RPC call when service
+        # connection caching is enabled. I believe this has something to do with
+        # the runtime code generation, but have not been able to diagnose it
+        # yet. For now, disable service connection caching for GCC environments.
+        kwargs["service_pool"] = ServiceConnectionPoolBase()
+
         super().__init__(
             *args,
             **kwargs,