Introduction to Parallel Programming

using Python Presented by: Samah Gad

July 11, 2013

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Road MapMotivationForking ProcessesThreadsInterprocess Communication - OverviewThe multiprocessing Module - Overview

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Motivation

Problem:Most computers spend a lot of time doing nothing.Majority of the modern CPU’s capacity is often spent in an idle state.

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Motivation -Cont.Solution:

Running more than one program at a time.

Dividing the CPU attention among a set of tasks.Parallel Processing, Multiprocessing, or Multitasking.

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Parallel Processing in Python

Two main ways to run tasks:Process forks Spawned threads

Python built-in tools like: os.fork, threading, queue, and multiprocessing.Third Party domains offers more advanced tools.

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Forking ProcessesTraditional ways to structure parallel tasks.Straight forward way to start an independent program.What is forking?

Copying programs.Python Module - os.fork

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Example 1

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Example 2

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Threads

Another way to start activities running at the same time.Lightweight processes

Run within the same single process.

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Threads - Advantages:

PerformanceSimplicityShared global memoryPortability

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Python ModulesPython Modules:

_thread modulethreading modules

Both modules provide tools for synchronizing access to shared objects with locks.

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The _thread Module

Start new independent threads of execution within a process.Doesn't support OOPPlatform independent module.

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Example 3

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Example 4

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Synchronizing access to shared objects and names

What is problem? Objects and namespaces in a process that span the life of threads are shared by all spawned threads.

Solution: Threads automatically come with a cross-task communications

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Example 5

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Threading Module

Internally uses the _thread module to implement objects that represent threads and common synchronization tools.Manage threads with high-level class-based objects.

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Example 6

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Interprocess Communication - Overview

Other solutions don’t support cross-program communication Sockets, Pipes, and SignalsEnable performing Inter-Process Communication (IPC)

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The multiprocessing Module - Overview

Provide the best of processes and threads.Platform independent.Uses processes instead of threads.Provide synchronizations tools.Leverage the capacity of multiple processors.

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