Write a multithreaded program that demonstrates RLock. Create two thread classes—Ad- dThread and MultiplyThread. Class AddThread should increment a global variable by 1, sleep for two seconds and increment the variable again. Class MultiplyThread should double the global variable,sleep for two second and double the variable again. Protect these critical sections with a lock. After both threads

Question

terminate, print the final value of the shared variable. Also, try commenting out lines so that the lock is not used. Notice the different value the variable has.

What will be an ideal response?

Answer 1

```
# Using an RLock to protect access to a critical section.

import threading
import time

class AddThread( threading.Thread ):
"""Subclass of threading.Thread"""

def __init__( self, threadName, lock ):
"""Initialize thread"""

threading.Thread.__init__( self, name = threadName )
self.lock = lock

def run( self ):
"""Modify data, sleep and modify again"""

global number

self.lock.acquire() # protect critical section

print self.getName(), "starting:", number
number += 1
print self.getName(), "sleeping:", number
time.sleep( 2 )
number += 1
print self.getName(), "done:", number

self.lock.release() # allow access to critical section

class MultiplyThread( threading.Thread ):
"""Subclass of threading.Thread"""

def __init__( self, threadName, lock ):
"""Initialize thread"""

threading.Thread.__init__( self, name = threadName )
self.lock = lock

def run( self ):
"""Modify data, sleep and modify again"""

global number

self.lock.acquire() # protect critical section

print self.getName(), "starting:", number
number *= 2
print self.getName(), "sleeping:", number
time.sleep( 2 )
number *= 2
print self.getName(), "done:", number

self.lock.release() # allow access to critical section

number = 1
lock = threading.RLock()

thread1 = AddThread( "thread1", lock )
thread2 = MultiplyThread( "thread2", lock )

thread1.start()
thread2.start()

thread1.join()
thread2.join()

print "Number is:", number
```
thread1 starting: 1
thread1 sleeping: 2
thread1 done: 3
thread2 starting: 3
thread2 sleeping: 6
thread2 done: 12
Number is: 12
thread1 starting: 1
thread1 sleeping: 2
thread2 starting: 2
thread2 sleeping: 4
thread1 done: 5
thread2 done: 10
Number is: 10