# HG changeset patch
# User paulb
# Date 1168815184 0
# Node ID 49367c7fd1043dd132e74e19e469edd984263926
# Parent  737f61472592824ed6b817ea21f89f7fba9de31f
[project @ 2007-01-14 22:53:04 by paulb]
Added a simple example of parallel computation.

diff -r 737f61472592 -r 49367c7fd104 examples/simple.py
--- a/examples/simple.py	Sun Jan 14 22:52:54 2007 +0000
+++ b/examples/simple.py	Sun Jan 14 22:53:04 2007 +0000
@@ -1,43 +1,70 @@
+#!/usr/bin/env python
+
+"""
+A simple example of parallel computation.
+"""
+
 import pprocess
 import time
 
-N = 10
+# Array size and a limit on the number of processes.
+
+N = 100
 limit = 10
 
 def make_array(n):
+
+    "Make an 'n' * 'n' array initialised with zeros."
+
     return [list(x) for x in [(0,) * n] * n]
 
 def calculate(ch, i, j):
+
+    """
+    A time-consuming calculation, using 'ch' to communicate with the parent
+    process, with 'i' and 'j' as operands.
+    """
+
     time.sleep(1)
     ch.send((i, j, i * N + j))
 
-def wait(exchange, D):
-    print "Processes:", len(exchange.active())
-    while len(exchange.active()) >= limit:
-        store(exchange, D)
+class MyExchange(pprocess.Exchange):
+
+    "Parallel convenience class containing the array assignment operation."
 
-def store(exchange, D):
-    for ch in exchange.ready():
+    def store_data(self, ch):
         i, j, result = ch.receive()
-        D[i][j] = result
+        self.D[i][j] = result
+
+# Main program.
 
 if __name__ == "__main__":
-    D = make_array(N)
-    exchange = pprocess.Exchange()
+
+    # Initialise the communications exchange with a limit on the number of
+    # channels/processes.
+
+    exchange = MyExchange(limit=limit)
+
+    # Initialise an array - it is stored in the exchange to permit automatic
+    # assignment of values as the data arrives.
+
+    exchange.D = make_array(N)
+
+    # The parallel computation.
 
     print "Calculating..."
     for i in range(0, N):
         for j in range(0, N):
             ch = pprocess.start(calculate, i, j)
-            wait(exchange, D)
-            exchange.add(ch)
+            exchange.add_wait(ch)
 
     print "Finishing..."
-    while exchange.active():
-        store(exchange, D)
+    exchange.finish()
+
+    # Show the result.
 
     print
-    for row in D:
+    for row in exchange.D:
         print row
 
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