add more concurrent examples

Concurrence_examples/getenv_example.py

@@ -0,0 +1,23 @@
+import time
+from gevent.pool import Pool
+from gevent import monkey
+ 
+# Note that you can spawn many workers with gevent since the cost of creating and switching is very low
+NUM_WORKERS = 4
+ 
+# Monkey-Patch socket module for HTTP requests
+monkey.patch_socket()
+ 
+start_time = time.time()
+ 
+pool = Pool(NUM_WORKERS)
+for address in WEBSITE_LIST:
+    pool.spawn(check_website, address)
+ 
+# Wait for stuff to finish
+pool.join()
+         
+end_time = time.time()        
+ 
+print("Time for GreenSquirrel: %ssecs" % (end_time - start_time))
+g