add mure concurrence examples

Concurrence_examples/multiprocessing_example.py

@@ -0,0 +1,14 @@
+import multiprocessing
+import time
+import random
+
+
+def worker(n):
+    sleep = random.randrange(1, 10)
+    time.sleep(sleep)
+    print("Worker {}: sleeping for {} seconds.".format(n, sleep))
+
+
+for i in range(5):
+    t = multiprocessing.Process(target=worker, args=(i,))
+    t.start()

Concurrence_examples/race_coditions.py

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+import threading
+
+x = 0     
+
+COUNT = 10000000
+
+def foo():
+    global x
+    for i in xrange(COUNT):
+        x += 1
+
+def bar():
+    global x
+    for i in xrange(COUNT):
+        x -= 1
+
+t1 = threading.Thread(target=foo)
+t2 = threading.Thread(target=bar)
+
+t1.start()
+t2.start()
+
+t1.join()
+t2.join()
+
+print(x)

Concurrence_examples/thread_example.py

@@ -0,0 +1,14 @@
+import time
+import random
+import threading
+
+
+def worker(n):
+    sleep = random.randrange(1, 10)
+    time.sleep(sleep)
+    print("Worker {}: sleeping for {} seconds.".format(n, sleep))
+
+
+for i in range(5):
+    t = threading.Thread(target=worker, args=(i,))
+    t.start()