Fix crash inside forked subprocess might leave SafeQueue in a locked state, causing task.close() to hang

clearml/utilities/process/mp.py

@@ -49,14 +49,18 @@ class ThreadCalls(object):
         self._queue.put((func, args))
         return True
 
-    def close(self):
+    def close(self, timeout=5.):
-        if not self._thread:
-            return
         t = self._thread
+        if not t:
+            return
+        try:
             # push something into queue so it knows this is the end
             self._queue.put(None)
-        # wait fot thread
+            # wait fot thread it should not take long, so we have a 5 second timeout
-        t.join()
+            # the background thread itself is doing nothing but push into a queue, so it should not take long
+            t.join(timeout=timeout)
+        except BaseException:  # noqa
+            pass
         # mark thread is done
         self._thread = None
 
@@ -76,6 +80,7 @@ class ThreadCalls(object):
                     request[0]()
             except Exception:
                 pass
+        self._thread = None
 
 
 class SingletonThreadPool(object):
@@ -110,8 +115,9 @@ class SafeQueue(object):
     def __init__(self, *args, **kwargs):
         self._reader_thread = None
         self._reader_thread_started = False
+        # Fix the python Queue and Use SimpleQueue write so it uses a single OS write,
+        # making it atomic message passing
         self._q = SimpleQueue(*args, **kwargs)
-        # Fix the simple queue write so it uses a single OS write, making it atomic message passing
         # noinspection PyBroadException
         try:
             # noinspection PyUnresolvedReferences,PyProtectedMember
@@ -129,17 +135,24 @@ class SafeQueue(object):
         # only call from main put process
         return self._q_size > 0
 
-    def close(self, event, timeout=100.0):
+    def close(self, event, timeout=3.0):
         # wait until all pending requests pushed
         tic = time()
+        prev_q_size = self._q_size
         while self.is_pending():
             if event:
                 event.set()
             if not self.__thread_pool.is_active():
                 break
             sleep(0.1)
+            # timeout is for the maximum time to pull a single object from the queue,
+            # this way if we get stuck we notice quickly and abort
             if timeout and (time()-tic) > timeout:
+                if prev_q_size == self._q_size:
                     break
+                else:
+                    prev_q_size = self._q_size
+                    tic = time()
 
     def get(self, *args, **kwargs):
         return self._get_internal_queue(*args, **kwargs)
@@ -169,7 +182,12 @@ class SafeQueue(object):
         self.__thread_pool.get().apply_async(self._q_put, args=(obj, ))
 
     def _q_put(self, obj):
+        try:
             self._q.put(obj)
+        except BaseException:
+            # make sure we zero the _q_size of the process dies (i.e. queue put fails)
+            self._q_size = 0
+            raise
         # GIL will make sure it is atomic
         self._q_size -= 1