Protect rootwrap daemon socket against multiple threads

Wrap the call with eventlet.Semaphore. Simultaneous Client.execute
calls can fail badly. Alternatively, rootwrap daemon connections
could be made every time when Client.execute is called, without
using a semaphore.

Change-Id: Id9d38832c67f2d81d382cda797a48fee943a27f1
Closes-bug: #1654287

oslo_rootwrap/client.py

@@ -47,11 +47,16 @@ class Client(object):
     def __init__(self, rootwrap_daemon_cmd):
         self._start_command = rootwrap_daemon_cmd
         self._initialized = False
+        self._need_restart = False
         self._mutex = threading.Lock()
         self._manager = None
         self._proxy = None
         self._process = None
         self._finalize = None
+        # This is for eventlet compatibility. multiprocessing stores
+        # daemon connection in ForkAwareLocal, so this won't be
+        # needed with the threading module.
+        self._exec_sem = threading.Lock()
 
     def _initialize(self):
         if self._process is not None and self._process.poll() is not None:
@@ -119,20 +124,40 @@ class Client(object):
                 self._proxy = None
                 self._initialized = False
                 self._initialize()
+                self._need_restart = False
             return self._proxy
 
-    def execute(self, cmd, stdin=None):
-        self._ensure_initialized()
-        proxy = self._proxy
-        retry = False
+    def _run_one_command(self, proxy, cmd, stdin):
+        """Wrap proxy.run_one_command, setting _need_restart on an exception.
+
+        Usually it should be enough to drain stale data on socket
+        rather than to restart, but we cannot do draining easily.
+        """
         try:
+            _need_restart = True
             res = proxy.run_one_command(cmd, stdin)
-        except (EOFError, IOError):
-            retry = True
-        # res can be None if we received final None sent by dying server thread
-        # instead of response to our request. Process is most likely to be dead
-        # at this point.
-        if retry or res is None:
-            proxy = self._restart(proxy)
-            res = proxy.run_one_command(cmd, stdin)
+            _need_restart = False
+            return res
+        finally:
+            if _need_restart:
+                self._need_restart = True
+
+    def execute(self, cmd, stdin=None):
+        with self._exec_sem:
+            self._ensure_initialized()
+            proxy = self._proxy
+            retry = False
+            if self._need_restart:
+                proxy = self._restart(proxy)
+            try:
+                res = self._run_one_command(proxy, cmd, stdin)
+            except (EOFError, IOError):
+                retry = True
+            # res can be None if we received final None sent by dying
+            # server thread instead of response to our
+            # request. Process is most likely to be dead at this
+            # point.
+            if retry or res is None:
+                proxy = self._restart(proxy)
+                res = self._run_one_command(proxy, cmd, stdin)
         return res

oslo_rootwrap/tests/test_functional_eventlet.py

@@ -25,3 +25,35 @@ if os.environ.get('TEST_EVENTLET', False):
         def assert_unpatched(self):
             # This test case is specifically for eventlet testing
             pass
+
+        def _thread_worker(self, seconds, msg):
+            code, out, err = self.execute(
+                ['sh', '-c', 'sleep %d; echo %s' % (seconds, msg)])
+            # Ignore trailing newline
+            self.assertEqual(msg, out.rstrip())
+
+        def _thread_worker_timeout(self, seconds, msg, timeout):
+            with eventlet.Timeout(timeout):
+                try:
+                    self._thread_worker(seconds, msg)
+                except eventlet.Timeout:
+                    pass
+
+        def test_eventlet_threads(self):
+            """Check eventlet compatibility.
+
+            The multiprocessing module is not eventlet friendly and
+            must be protected against eventlet thread switching and its
+            timeout exceptions.
+            """
+            th = []
+            # 10 was not enough for some reason.
+            for i in range(15):
+                th.append(
+                    eventlet.spawn(self._thread_worker, i % 3, 'abc%d' % i))
+            for i in [5, 17, 20, 25]:
+                th.append(
+                    eventlet.spawn(self._thread_worker_timeout, 2,
+                                   'timeout%d' % i, i))
+            for thread in th:
+                thread.wait()