Rework join to wait once for all threads and not once per thread

Author: benoit74

src/zimscraperlib/executor.py

@@ -85,6 +85,8 @@ def start(self):
         """Enable executor, starting requested amount of workers
 
         Workers are started always, not provisioned dynamically"""
+        logger.debug(f"Starting {self.executor_name} with {self.nb_workers} threads")
+
         self.drain()
         self._workers: set[threading.Thread] = set()
         self.no_more = False
@@ -139,26 +141,30 @@ def drain(self):
 
     def join(self):
         """Await completion of workers, requesting them to stop taking new task"""
-        logger.debug(f"joining all threads for {self.executor_name}")
+        logger.debug(
+            f"joining all threads for {self.executor_name}; threads have "
+            f"{self.thread_deadline_sec}s to join before we give-up waiting for them"
+        )
         self.no_more = True
-        for num, t in enumerate(self._workers):
-            deadline = datetime.datetime.now(tz=datetime.UTC) + datetime.timedelta(
-                seconds=self.thread_deadline_sec
-            )
-            logger.debug(
-                f"Giving {self.executor_name}-{num} {self.thread_deadline_sec}s to join"
-            )
+        deadline = datetime.datetime.now(tz=datetime.UTC) + datetime.timedelta(
+            seconds=self.thread_deadline_sec
+        )
+        alive_threads = list(filter(lambda t: t.is_alive(), self._workers))
+        for t in filter(lambda t: t not in alive_threads, self._workers):
+            logger.debug(f"Thread {t.name} is already dead. Skipping…")
+        while (
+            len(alive_threads) > 0 and datetime.datetime.now(tz=datetime.UTC) < deadline
+        ):
             e = threading.Event()
-            while t.is_alive() and datetime.datetime.now(tz=datetime.UTC) < deadline:
-                t.join(1)
-                e.wait(timeout=2)
-            if t.is_alive():
-                logger.debug(
-                    f"Thread {self.executor_name}-{num} is not joining. Skipping…"
-                )
-            else:
-                logger.debug(f"Thread {self.executor_name}-{num} joined")
-        logger.debug(f"all threads joined for {self.executor_name}")
+            for t in alive_threads:
+                t.join(0.1)  # just indicate to the thread that we want to stop
+            e.wait(2)  # wait a bit more to let things cool down
+            for t in filter(lambda t: not t.is_alive(), alive_threads):
+                logger.debug(f"Thread {t.name} joined")
+                alive_threads.remove(t)
+        for t in alive_threads:
+            logger.debug(f"Thread {t.name} never joined. Skipping…")
+        logger.debug(f"join completed for {self.executor_name}")
 
     def shutdown(self, *, wait=True):
         """stop the executor, either somewhat immediately or awaiting completion"""