adding chapter 7 source code

Chapter7/multithreading/thread3a.py

@@ -0,0 +1,27 @@
+# thread3a.py when no thread synchronization used
+
+from threading import Thread as Thread
+
+def inc():
+    global x
+    for _ in range(1000000):
+        x+=1
+
+#global variable
+x = 0
+
+# creating threads
+t1 = Thread(target=inc, name="Th 1")
+t2 = Thread(target=inc, name="Th 2")
+
+# start the threads
+t1.start()
+t2.start()
+
+#wait for the threads
+t1.join()
+t2.join()
+
+print("final value of x :", x)
+
+