Data commit

Task/Atomic-updates/Python/atomic-updates.py

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+from __future__ import with_statement # required for Python 2.5
+import threading
+import random
+import time
+
+terminate = threading.Event()
+
+class Buckets:
+    def __init__(self, nbuckets):
+        self.nbuckets = nbuckets
+        self.values = [random.randrange(10) for i in range(nbuckets)]
+        self.lock = threading.Lock()
+
+    def __getitem__(self, i):
+        return self.values[i]
+
+    def transfer(self, src, dst, amount):
+        with self.lock:
+            amount = min(amount, self.values[src])
+            self.values[src] -= amount
+            self.values[dst] += amount
+
+    def snapshot(self):
+        # copy of the current state (synchronized)
+        with self.lock:
+            return self.values[:]
+
+def randomize(buckets):
+    nbuckets = buckets.nbuckets
+    while not terminate.isSet():
+        src = random.randrange(nbuckets)
+        dst = random.randrange(nbuckets)
+        if dst!=src:
+            amount = random.randrange(20)
+            buckets.transfer(src, dst, amount)
+
+def equalize(buckets):
+    nbuckets = buckets.nbuckets
+    while not terminate.isSet():
+        src = random.randrange(nbuckets)
+        dst = random.randrange(nbuckets)
+        if dst!=src:
+            amount = (buckets[src] - buckets[dst]) // 2
+            if amount>=0: buckets.transfer(src, dst, amount)
+            else: buckets.transfer(dst, src, -amount)
+
+def print_state(buckets):
+    snapshot = buckets.snapshot()
+    for value in snapshot:
+        print '%2d' % value,
+    print '=', sum(snapshot)
+
+# create 15 buckets
+buckets = Buckets(15)
+
+# the randomize thread
+t1 = threading.Thread(target=randomize, args=[buckets])
+t1.start()
+
+# the equalize thread
+t2 = threading.Thread(target=equalize, args=[buckets])
+t2.start()
+
+# main thread, display
+try:
+    while True:
+        print_state(buckets)
+        time.sleep(1)
+except KeyboardInterrupt: # ^C to finish
+    terminate.set()
+
+# wait until all worker threads finish
+t1.join()
+t2.join()