Data commit

Task/Dining-philosophers/Python/dining-philosophers.py

@@ -0,0 +1,67 @@
+import threading
+import random
+import time
+
+# Dining philosophers, 5 Phillies with 5 forks. Must have two forks to eat.
+#
+# Deadlock is avoided by never waiting for a fork while holding a fork (locked)
+# Procedure is to do block while waiting to get first fork, and a nonblocking
+# acquire of second fork.  If failed to get second fork, release first fork,
+# swap which fork is first and which is second and retry until getting both.
+#
+# See discussion page note about 'live lock'.
+
+class Philosopher(threading.Thread):
+
+    running = True
+
+    def __init__(self, xname, forkOnLeft, forkOnRight):
+        threading.Thread.__init__(self)
+        self.name = xname
+        self.forkOnLeft = forkOnLeft
+        self.forkOnRight = forkOnRight
+
+    def run(self):
+        while(self.running):
+            #  Philosopher is thinking (but really is sleeping).
+            time.sleep( random.uniform(3,13))
+            print '%s is hungry.' % self.name
+            self.dine()
+
+    def dine(self):
+        fork1, fork2 = self.forkOnLeft, self.forkOnRight
+
+        while self.running:
+            fork1.acquire(True)
+            locked = fork2.acquire(False)
+            if locked: break
+            fork1.release()
+            print '%s swaps forks' % self.name
+            fork1, fork2 = fork2, fork1
+        else:
+            return
+
+        self.dining()
+        fork2.release()
+        fork1.release()
+
+    def dining(self):			
+        print '%s starts eating '% self.name
+        time.sleep(random.uniform(1,10))
+        print '%s finishes eating and leaves to think.' % self.name
+
+def DiningPhilosophers():
+    forks = [threading.Lock() for n in range(5)]
+    philosopherNames = ('Aristotle','Kant','Spinoza','Marx', 'Russel')
+
+    philosophers= [Philosopher(philosopherNames[i], forks[i%5], forks[(i+1)%5]) \
+            for i in range(5)]
+
+    random.seed(507129)
+    Philosopher.running = True
+    for p in philosophers: p.start()
+    time.sleep(100)
+    Philosopher.running = False
+    print ("Now we're finishing.")
+
+DiningPhilosophers()