Part 15 - Functions as Objects and Multithreading

Added by Cameron Kenneth Knight, last edited by Cameron Kenneth Knight on Sep 10, 2005  (view change)

Part 15 - Functions as Objects and Multithreading

Having Functions act as objects exposes three very useful methods:

  1. function.Invoke(<arguments>) as <return type>
  2. function.BeginInvoke(<arguments>) as IAsyncResult
  3. function.EndInvoke(IAsyncResult) as <return type>

.Invoke just calls the function normally and acts like it was called with just regular parentheses ().
.BeginInvoke starts a seperate thread that does nothing but run the function invoked.
.EndInvoke finishes up the previously invoked function and returns the proper return type.

example of .Invoke
def Nothing(x):
    return x

i = 5
assert 5 == Nothing(i)
assert i == Nothing.Invoke(i)
assert i == Nothing.Invoke.Invoke(i)

Since .Invoke is a function itself, it has its own .Invoke.

Here's a good example of .BeginInvoke

Multithreading with .BeginInvoke
import System
import System.Threading

class FibonacciCalculator:
    def constructor():
        _alpha, _beta = 0, 1
        _stopped = true
    
    def Calculate():
        _stopped = false
        while not _stopped:
            Thread.Sleep(200)
            _alpha, _beta = _beta, _alpha + _beta
            print _beta
    
    def Start():
        _result = Calculate.BeginInvoke()
    
    def Stop():
        _stopped = true
        Calculate.EndInvoke(_result)

    _result as IAsyncResult
    
    _alpha as ulong
    _beta as ulong
    
    _stopped as bool

fib = FibonacciCalculator()
fib.Start()
prompt("Press enter to stop...\n")
fib.Stop()

The output produces the Fibonacci sequence roughly every 200 milliseconds (because that's what the delay is). This will produce an overflow after it gets up to 2^64.
The important thing is that it stops cleanly if you press Enter.

Exercises

  1. Think of an exercise

Go on to Part 16 - Generators

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