lec2b.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "de014d74-4685-4f16-85fd-f571fd5a91db",
   "metadata": {},
   "outputs": [],
   "source": [
    "import threading"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "82b2f08c-1a13-4a0f-9546-e5d624dbee5b",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  0           RESUME                   0\n",
      "\n",
      "  1           LOAD_NAME                0 (total)\n",
      "              LOAD_CONST               0 (1)\n",
      "              BINARY_OP               13 (+=)\n",
      "              STORE_NAME               0 (total)\n",
      "              RETURN_CONST             1 (None)\n"
     ]
    }
   ],
   "source": [
    "import dis\n",
    "dis.dis(\"total += 1\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "ae617ed8-dd51-4154-ad83-308df527d1f1",
   "metadata": {},
   "outputs": [],
   "source": [
    "import threading"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "b735264e-f27a-4d27-ba5f-4d6a1f53543e",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "CPU times: user 151 ms, sys: 0 ns, total: 151 ms\n",
      "Wall time: 148 ms\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "2000000"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "%%time\n",
    "# 141 ms (no locks)\n",
    "# 340 ms (fine-grained locking)\n",
    "# 122 ms (coarse-grained locking)\n",
    "\n",
    "lock = threading.Lock() # this protects total\n",
    "total = 0\n",
    "\n",
    "def task(count):\n",
    "    global total\n",
    "    lock.acquire()\n",
    "    for i in range(count):\n",
    "        total += 1\n",
    "    lock.release()\n",
    "\n",
    "t1 = threading.Thread(target=task, args=[1_000_000])\n",
    "t1.start()\n",
    "t2 = threading.Thread(target=task, args=[1_000_000])\n",
    "t2.start()\n",
    "\n",
    "t1.join()\n",
    "t2.join()\n",
    "\n",
    "total"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "7cf83d46-b7db-4ab6-b0bb-4b35fecba5b2",
   "metadata": {},
   "outputs": [],
   "source": [
    "bank_accounts = {\"x\": 25, \"y\": 100, \"z\": 200} # in dollars\n",
    "lock = threading.Lock() # protects bank_accounts\n",
    "\n",
    "def transfer(src, dst, amount):\n",
    "    with lock: # automatically acquire now, automatically release after the with\n",
    "        success = False\n",
    "        if bank_accounts[src] >= amount:\n",
    "            bank_accounts[src] -= amount\n",
    "            bank_accounts[dst] += amount\n",
    "            success = True\n",
    "        print(\"transferred\" if success else \"denied\")\n",
    "        print(\"is it locked inside the with?\", lock.locked())\n",
    "    print(\"is it locked after the with?\", lock.locked())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "c9f19a3d-172f-4103-b631-11b42a8dc94c",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "transferred\n",
      "is it locked inside the with? True\n",
      "is it locked after the with? False\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "{'x': 5, 'y': 120, 'z': 200}"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "transfer(\"x\", \"y\", 20)\n",
    "bank_accounts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "bdd94c73-dd01-4b9e-aecc-70faff00685d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "denied\n",
      "is it locked inside the with? True\n",
      "is it locked after the with? False\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "{'x': 5, 'y': 120, 'z': 200}"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "transfer(\"x\", \"z\", 10)\n",
    "bank_accounts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "41f9d7d2-86f8-433c-bf56-724a7f445753",
   "metadata": {},
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "'w'",
     "output_type": "error",
     "traceback": [
      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[0;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "Cell \u001b[0;32mIn[8], line 1\u001b[0m\n\u001b[0;32m----> 1\u001b[0m \u001b[43mtransfer\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[38;5;124;43mw\u001b[39;49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[38;5;124;43mz\u001b[39;49m\u001b[38;5;124;43m\"\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[38;5;241;43m10\u001b[39;49m\u001b[43m)\u001b[49m \u001b[38;5;66;03m# there is no \"w\" bank account\u001b[39;00m\n\u001b[1;32m      2\u001b[0m bank_accounts\n",
      "Cell \u001b[0;32mIn[5], line 7\u001b[0m, in \u001b[0;36mtransfer\u001b[0;34m(src, dst, amount)\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[38;5;28;01mwith\u001b[39;00m lock: \u001b[38;5;66;03m# automatically acquire now, automatically release after the with\u001b[39;00m\n\u001b[1;32m      6\u001b[0m     success \u001b[38;5;241m=\u001b[39m \u001b[38;5;28;01mFalse\u001b[39;00m\n\u001b[0;32m----> 7\u001b[0m     \u001b[38;5;28;01mif\u001b[39;00m \u001b[43mbank_accounts\u001b[49m\u001b[43m[\u001b[49m\u001b[43msrc\u001b[49m\u001b[43m]\u001b[49m \u001b[38;5;241m>\u001b[39m\u001b[38;5;241m=\u001b[39m amount:\n\u001b[1;32m      8\u001b[0m         bank_accounts[src] \u001b[38;5;241m-\u001b[39m\u001b[38;5;241m=\u001b[39m amount\n\u001b[1;32m      9\u001b[0m         bank_accounts[dst] \u001b[38;5;241m+\u001b[39m\u001b[38;5;241m=\u001b[39m amount\n",
      "\u001b[0;31mKeyError\u001b[0m: 'w'"
     ]
    }
   ],
   "source": [
    "transfer(\"w\", \"z\", 10) # there is no \"w\" bank account\n",
    "bank_accounts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "f193975b-6f75-4c3c-b789-c494ad1130a6",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "transferred\n",
      "is it locked inside the with? True\n",
      "is it locked after the with? False\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "{'x': 5, 'y': 170, 'z': 150}"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "transfer(\"z\", \"y\", 50)\n",
    "bank_accounts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "cd9dd92a-3d2c-47c7-85f1-4bec952d1a67",
   "metadata": {},
   "outputs": [],
   "source": []
  }
 ],
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