File backport_run_in_executor.patch of Package python-flower

From 5741cbcbc5c2a75c2552326018ee97b8fe5f257f Mon Sep 17 00:00:00 2001
From: John Vandenberg <jayvdb@gmail.com>
Date: Fri, 22 Mar 2019 08:28:34 +0700
Subject: [PATCH] Backport run_in_executor

---
 flower/api/tasks.py | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/flower/api/tasks.py b/flower/api/tasks.py
index 1f172422..f0395dea 100644
--- a/flower/api/tasks.py
+++ b/flower/api/tasks.py
@@ -78,6 +78,24 @@ def safe_result(self, result):
             return result
 
 
+def inline_run_in_executor(func, *args):
+    from tornado.concurrent import Future, chain_future
+
+    io_loop = IOLoop.current()
+    if not hasattr(io_loop, "_executor"):
+        import concurrent.futures
+        from tornado.process import cpu_count
+
+        io_loop._executor = concurrent.futures.ThreadPoolExecutor(
+            max_workers=(cpu_count() * 5)
+        )
+    executor = io_loop._executor
+    c_future = executor.submit(func, *args)
+    t_future = Future()
+    io_loop.add_future(c_future, lambda f: chain_future(f, t_future))
+    return t_future
+
+
 class TaskApply(BaseTaskHandler):
     @web.authenticated
     @gen.coroutine
@@ -138,8 +156,7 @@ def post(self, taskname):
         result = task.apply_async(args=args, kwargs=kwargs, **options)
         response = {'task-id': result.task_id}
 
-        response = yield IOLoop.current().run_in_executor(
-            None, self.wait_results, result, response)
+        response = yield inline_run_in_executor(self.wait_results, result, response)
         self.write(response)
 
     def wait_results(self, result, response):