Fix LD_LIBRARY_PATH race conditions

Some providers need additional libraries, specified through
the LD_LIBRARY_PATH env variable.

The problem is that we're modifying os.environ globally before
starting the process. This leads to race conditions when
spawning multiple subprocesses at the same time.

For this reason, we'll use a lock.

coriolis/worker/rpc/server.py

@@ -7,6 +7,7 @@ import os
 import shutil
 import signal
 import sys
+import threading
 import time
 
 from oslo_config import cfg
@@ -49,6 +50,7 @@ class WorkerServerEndpoint(object):
         self._server = utils.get_hostname()
         self._service_registration = self._register_worker_service()
         self._rpc_conductor_client_instance = None
+        self._lock = threading.Lock()
 
     @property
     def _rpc_conductor_client(self):
@@ -166,20 +168,23 @@ class WorkerServerEndpoint(object):
         param extra_library_paths: list(str): list of paths with extra
         libraries which should be available to the worker process.
         """
-        original_ld_path = os.environ.get('LD_LIBRARY_PATH', "")
-        LOG.debug(
-            "Starting new worker process with extra libraries: '%s'",
-            extra_library_paths)
-        try:
-            os.environ['LD_LIBRARY_PATH'] = self._get_custom_ld_path(
-                original_ld_path, extra_library_paths)
-            process.start()
-        except TypeError:
-            LOG.warning(
-                "Failed to set extra library paths: %s. Error was: %s",
-                extra_library_paths, utils.get_exception_details())
-        finally:
-            os.environ['LD_LIBRARY_PATH'] = original_ld_path
+        # We're modifying the "os.environ" globally. To avoid race conditions,
+        # we need to use a lock.
+        with self._lock:
+            original_ld_path = os.environ.get('LD_LIBRARY_PATH', "")
+            LOG.debug(
+                "Starting new worker process with extra libraries: '%s'",
+                extra_library_paths)
+            try:
+                os.environ['LD_LIBRARY_PATH'] = self._get_custom_ld_path(
+                    original_ld_path, extra_library_paths)
+                process.start()
+            except TypeError:
+                LOG.warning(
+                    "Failed to set extra library paths: %s. Error was: %s",
+                    extra_library_paths, utils.get_exception_details())
+            finally:
+                os.environ['LD_LIBRARY_PATH'] = original_ld_path
 
     def _get_extra_library_paths_for_providers(
             self, ctxt, task_id, task_type, origin, destination):