add all concurrence examples

Concurrence_examples/concurrence_future_example.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import random
 import logging
 import concurrent.futures

Concurrence_examples/concurrent_tasks.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import os
 import time
 import threading

Concurrence_examples/concurrent_tasks_with_math.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import os
 import time
 import threading

Concurrence_examples/getenv_example.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import time
 from gevent.pool import Pool
 from gevent import monkey
@@ -20,4 +22,3 @@ pool.join()
 end_time = time.time()        
  
 print("Time for GreenSquirrel: %ssecs" % (end_time - start_time))
-g

Concurrence_examples/multiprocessing_example.py

@@ -1,6 +1,8 @@
-import multiprocessing
+#!/usr/bin/env python3
+
 import time
 import random
+import multiprocessing
 
 
 def worker(n):

Concurrence_examples/pool_example.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+
+from multiprocessing import Pool
+
+def f(x):
+    return x*x
+
+if __name__ == '__main__':
+    p = Pool(5)
+    print(p.map(f, [1, 2, 3]))

Concurrence_examples/race_coditions.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import threading
 
 x = 0     

Concurrence_examples/safe_thread_example.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import threading
 
 counter = 0

Concurrence_examples/thread_example.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import time
 import random
 import threading

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())

Concurrence_examples/threads_with_queues.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import time
 from queue import Queue
 from threading import Thread

Concurrence_examples/unsafe_thread_example.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 import time
 import threading