import threading
import sys
import time
"""
States represent the philosopher state in any moment
"""
class States:
Thinking, Hungry, Eating = range( 0, 3 )
"""
Represents the Silberschatz solution using a monitor
We use a lock to allow only one thead running in all 'public' (PickUp, and PutDown) methods of this class
Each chopstick is represented by a Condition variable
"""
class DiningPhi:
# Instance variables
n = 0
lock = 0
state = []
chopstick = []
# Class variable initialization
def __init__( self, number ):
self.lock = threading.Lock()
self.n = number
self.chopstick = [threading.Condition( self.lock ) for i in range( number ) ]
self.state = [ States.Thinking for i in range( number ) ]
# Called when a philosopher wants to eat, and needs to pickup two chopsticks
def PickUp( self, who ):
with self.lock:
self.state[ who ] = States.Hungry
self.Test( who )
if ( self.state[ who ] == States.Hungry ):
self.chopstick[ who ].wait( )
# Called when a philosopher finish eating and needs to return his two chopsticks
def PutDown( self, who ):
with self.lock:
self.state[ who ] = States.Thinking
self.Test( ( who + (self.n - 1) ) % self.n )
self.Test( ( who + 1 ) % self.n )
# Check if a philosopher can pickup his two chopsticks, if none of his neighbor are not eating
# Additionally check when a philosopher are returning his chopstick if one of his neighbor are Hungry
def Test( self, who ):
if ( ( self.state[ (who + (self.n - 1) ) % self.n ] != States.Eating ) and
( self.state[ (who + 1) % self.n ] != States.Eating ) and
( self.state[ who ] == States.Hungry ) ):
self.state[ who ] = States.Eating
self.chopstick[ who ].notify( )
# Print table status
def Print( self, who ):
desc = [ 'Thinking', 'Hungry', 'Eating' ]
with self.lock:
sys.stdout.write( "Filo %s [ " % who )
[ sys.stdout.write( " %s, " % desc[ self.state[ i ] ] ) for i in range( self.n ) ]
sys.stdout.write( "]\n" )
# Code for the thread representing each philosopher
def Filosofo( who, mesa ):
for i in range(10):
time.sleep(0.1) # think
sys.stdout.write( " Filosofo %s va a tomar palillos \n" % who )
mesa.PickUp( who )
sys.stdout.write( " Filosofo %s esta comiendo \n" % who )
time.sleep(0.1) # (yield makes deadlock more likely)
mesa.PutDown( who )
sys.stdout.write( " Filosofo %s va a pensar \n" % who )
time.sleep(0.1 * who )
mesa.Print( who )
# Code to start simulation, original problem states five philosophers
def Festin( number ):
mesa = DiningPhi( number )
for i in range( number ):
t = threading.Thread( target=Filosofo, args=(i, mesa) )
t.start()
def main():
Festin( 5 )
if __name__ == "__main__":
main()
