adding chapter 7 source code

Chapter7/multithreading/thread3b.py

@@ -0,0 +1,27 @@
+# thread3b.py when  thread synchronization is used
+
+from threading import Lock, Thread as Thread
+
+def inc_with_lock (lock):
+    global x
+    for _ in range(1000000):
+        lock.acquire()
+        x+=1
+        lock.release()
+
+x = 0
+mylock = Lock()
+# creating threads
+t1 = Thread(target=inc_with_lock , args=(mylock,), name="Th 1")
+t2 = Thread(target=inc_with_lock , args=(mylock,), name="Th 2")
+
+# start the threads
+t1.start()
+t2.start()
+
+#wait for the threads
+t1.join()
+t2.join()
+print("final value of x :", x)
+
+