{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Introduction to Multiprocessing in Python\n",
    "Adapted from: \"LucidProgramming\" [1](https://github.com/vprusso/youtube_tutorials/tree/master/multiprocessing_and_threading)\n",
    "\n",
    "Multiprocessing docs: [2](https://docs.python.org/3.7/library/multiprocessing.html)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import time\n",
    "import os\n",
    "print(os.cpu_count())\n",
    "from multiprocessing import cpu_count\n",
    "print(cpu_count())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Processes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "from multiprocessing import Process, current_process"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# an example function\n",
    "\n",
    "def example(t):\n",
    "    # Process ID assigned by Python\n",
    "    proc_name = current_process().name\n",
    "    # Process ID assigned by system\n",
    "    proc_id = os.getpid()\n",
    "    time.sleep(t)\n",
    "    print(f\"Process {proc_name} ({proc_id}) waited {t} seconds\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "times = [5, 4, 3, 2, 1]\n",
    "proc_list = []\n",
    "\n",
    "for t in times:\n",
    "    proc = Process(target=example, args=(t,))\n",
    "    proc_list.append(proc)\n",
    "    proc.start()\n",
    "\n",
    "for proc in proc_list:\n",
    "    proc.join()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "proc_list = []\n",
    "\n",
    "for _ in range(100):\n",
    "    proc = Process(target=example, args=(10,))\n",
    "    proc_list.append(proc)\n",
    "    proc.start()\n",
    "    \n",
    "for proc in proc_list:\n",
    "    proc.join()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Pool"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# YouTube Link: https://www.youtube.com/watch?v=u2jTn-Gj2Xw\n",
    "\n",
    "# One can create a pool of processes which will carry out tasks submitted to\n",
    "# it with the Pool class.\n",
    "\n",
    "# A process pool object which controls a pool of worker processes to which\n",
    "# jobs can be submitted. It supports asynchronous results with timeouts and\n",
    "# callbacks and has a parallel map implementation.\n",
    "\n",
    "import time\n",
    "from multiprocessing import Pool\n",
    "\n",
    "\n",
    "# contrived CPU intensive task\n",
    "def sum_square(numbers):\n",
    "    s = 0\n",
    "    for i in range(numbers):\n",
    "        s += i * i\n",
    "    return s\n",
    "\n",
    "\n",
    "def sum_square_with_mp(numbers):\n",
    "\n",
    "    start_time = time.time()\n",
    "    p = Pool()\n",
    "    result = p.map(sum_square, numbers)\n",
    "\n",
    "    p.close()\n",
    "    p.join()\n",
    "\n",
    "    end_time = time.time() - start_time\n",
    "\n",
    "    print(f\"Processing {len(numbers)} numbers took {end_time} time using multiprocessing.\")\n",
    "\n",
    "\n",
    "def sum_square_no_mp(numbers):\n",
    "\n",
    "    start_time = time.time()\n",
    "    result = []\n",
    "\n",
    "    for i in numbers:\n",
    "        result.append(sum_square(i))\n",
    "    end_time = time.time() - start_time\n",
    "\n",
    "    print(f\"Processing {len(numbers)} numbers took {end_time} time using serial processing.\")\n",
    "\n",
    "numbers = range(10000)\n",
    "sum_square_with_mp(numbers)\n",
    "sum_square_no_mp(numbers)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Locks"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# YouTube Link: https://www.youtube.com/watch?v=iYJNmuD4McE\n",
    "\n",
    "# A lock or mutex is a sychronization mechanism for enforcing\n",
    "# limits on access to a resource in an environment where there\n",
    "# are many threads of execution.\n",
    "\n",
    "# More on locks:\n",
    "# https://en.wikipedia.org/wiki/Lock_(computer_science)\n",
    "\n",
    "from multiprocessing import Process, Lock, Value\n",
    "\n",
    "\n",
    "def add_500_no_mp(total):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        total += 5\n",
    "    return total\n",
    "\n",
    "\n",
    "def sub_500_no_mp(total):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        total -= 5\n",
    "    return total\n",
    "\n",
    "\n",
    "def add_500_no_lock(total):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        total.value += 5\n",
    "\n",
    "\n",
    "def sub_500_no_lock(total):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        total.value -= 5\n",
    "\n",
    "\n",
    "def add_500_lock(total, lock):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        lock.acquire()\n",
    "        total.value += 5\n",
    "        lock.release()\n",
    "\n",
    "\n",
    "def sub_500_lock(total, lock):\n",
    "    for i in range(100):\n",
    "        time.sleep(0.01)\n",
    "        lock.acquire()\n",
    "        total.value -= 5\n",
    "        lock.release()\n",
    "\n",
    "total = Value('i', 500)\n",
    "\n",
    "add_proc = Process(target=add_500_no_lock, args=(total,))\n",
    "sub_proc = Process(target=sub_500_no_lock, args=(total,))\n",
    "\n",
    "#lock = Lock()\n",
    "#add_proc = Process(target=add_500_lock, args=(total, lock))\n",
    "#sub_proc = Process(target=sub_500_lock, args=(total, lock))\n",
    "\n",
    "add_proc.start()\n",
    "sub_proc.start()\n",
    "\n",
    "add_proc.join()\n",
    "sub_proc.join()\n",
    "print(total.value)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Queues"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# YouTube Link: https://www.youtube.com/watch?v=TQx3IfCVvQ0\n",
    "\n",
    "# We show how to make use of the multiprocessing Queue class to communicate\n",
    "# between different processes.\n",
    "\n",
    "\n",
    "from multiprocessing import Process, Queue\n",
    "\n",
    "\n",
    "def square(numbers, queue):\n",
    "    for i in numbers:\n",
    "        queue.put(i*i)\n",
    "\n",
    "\n",
    "def cube(numbers, queue):\n",
    "    for i in numbers:\n",
    "        queue.put(i*i*i)\n",
    "\n",
    "\n",
    "numbers = range(5)\n",
    "\n",
    "queue = Queue()\n",
    "square_process = Process(target=square, args=(numbers, queue))\n",
    "cube_process = Process(target=cube, args=(numbers, queue))\n",
    "\n",
    "square_process.start()\n",
    "cube_process.start()\n",
    "\n",
    "square_process.join()\n",
    "cube_process.join()\n",
    "\n",
    "while not queue.empty():\n",
    "    print(queue.get())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Pipes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "from multiprocessing import Process, Pipe\n",
    "\n",
    "def f(conn):\n",
    "    conn.send([42, None, 'hello'])\n",
    "    conn.close()\n",
    "\n",
    "a, b = Pipe()\n",
    "p = Process(target=f, args=(a,))\n",
    "p.start()\n",
    "print(b.recv())   # prints \"[42, None, 'hello']\"\n",
    "p.join()"
   ]
  }
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