add all concurrence examples

Concurrence_examples/threadpool_example.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+
+from time import sleep
+from concurrent.futures import ThreadPoolExecutor
+
+ 
+def return_after_5_secs(message):
+    sleep(5)
+    return message
+ 
+pool = ThreadPoolExecutor(3)
+
+ 
+future = pool.submit(return_after_5_secs, ("hello"))
+print(future.done())
+sleep(5)
+print(future.done())
+print(future.result())