1 00:00:01,190 --> 00:00:02,840 ‫Let's now write some code 2 00:00:02,840 --> 00:00:05,520 ‫in order to get a better understanding 3 00:00:05,520 --> 00:00:07,893 ‫of what happens in the event loop. 4 00:00:09,200 --> 00:00:11,370 ‫So just like before, to get started 5 00:00:11,370 --> 00:00:13,670 ‫with the coding part of this section, 6 00:00:13,670 --> 00:00:15,970 ‫go ahead and grab the starter files 7 00:00:15,970 --> 00:00:18,550 ‫for this section, copy them somewhere, 8 00:00:18,550 --> 00:00:22,050 ‫and then open up the project in your code editor. 9 00:00:22,050 --> 00:00:24,310 ‫So I have it here on the desktop, 10 00:00:24,310 --> 00:00:27,550 ‫and in my VSCode, and all we have here to start 11 00:00:27,550 --> 00:00:31,420 ‫is this test-file.txt, and so I'm gonna create 12 00:00:31,420 --> 00:00:35,033 ‫a new file here, and I'm gonna call it the event-loop.js. 13 00:00:38,040 --> 00:00:41,530 ‫Alright, now it is actually extremely difficult 14 00:00:41,530 --> 00:00:44,000 ‫to simulate the event loop properly, 15 00:00:44,000 --> 00:00:46,400 ‫because we can't really put many callbacks 16 00:00:46,400 --> 00:00:48,080 ‫in all the callback queues that we 17 00:00:48,080 --> 00:00:51,260 ‫talked about before all at the same time, right. 18 00:00:51,260 --> 00:00:53,710 ‫That situation happens when for example 19 00:00:53,710 --> 00:00:56,360 ‫a lot of requests are coming into your app, 20 00:00:56,360 --> 00:01:00,240 ‫but here locally, that's just very hard to replicate. 21 00:01:00,240 --> 00:01:03,150 ‫But anyway, we will still do some very interesting 22 00:01:03,150 --> 00:01:05,390 ‫experiments using some of the stuff 23 00:01:05,390 --> 00:01:07,540 ‫that we learned in the last video. 24 00:01:07,540 --> 00:01:09,830 ‫And what we're gonna do is to write a bunch 25 00:01:09,830 --> 00:01:12,190 ‫of lines of code, and then try to figure out 26 00:01:12,190 --> 00:01:15,130 ‫in which order they should be executed 27 00:01:15,130 --> 00:01:17,950 ‫in the event loop, and analyze if the results 28 00:01:17,950 --> 00:01:20,360 ‫that we get actually make sense. 29 00:01:20,360 --> 00:01:22,710 ‫So let's start by writing a setTimeout, 30 00:01:24,290 --> 00:01:26,513 ‫so basically in order to set a timer, 31 00:01:27,980 --> 00:01:29,890 ‫and I'm using an arrow function here, 32 00:01:29,890 --> 00:01:31,270 ‫and the only thing that I'm gonna do 33 00:01:31,270 --> 00:01:33,773 ‫is to log to console some string, 34 00:01:34,930 --> 00:01:39,930 ‫so console.log, timer one finished, 35 00:01:41,800 --> 00:01:45,390 ‫and I want this to expire right after zero seconds. 36 00:01:45,390 --> 00:01:47,740 ‫Okay, give it a save, and then you see 37 00:01:47,740 --> 00:01:50,030 ‫that it actually corrected this string here, 38 00:01:50,030 --> 00:01:53,120 ‫so it changed this quotes, and added the semicolon, 39 00:01:53,120 --> 00:01:54,810 ‫and that's because of the Prettier 40 00:01:54,810 --> 00:01:56,940 ‫extension that we installed before. 41 00:01:56,940 --> 00:01:58,510 ‫Now I'm not gonna configure it here, 42 00:01:58,510 --> 00:01:59,850 ‫because for this small example, 43 00:01:59,850 --> 00:02:02,050 ‫that's not really necessary, okay. 44 00:02:02,050 --> 00:02:05,150 ‫So that is setting a timer, then let's also use 45 00:02:05,150 --> 00:02:09,320 ‫setImmediate, so remember that from the last video. 46 00:02:09,320 --> 00:02:11,620 ‫Okay, now I'm not gonna explain a lot here, 47 00:02:11,620 --> 00:02:13,350 ‫for now let's write this code, 48 00:02:13,350 --> 00:02:15,510 ‫and then analyze what happens, okay. 49 00:02:15,510 --> 00:02:20,320 ‫So setImmediate, and just like the other timer, 50 00:02:20,320 --> 00:02:22,500 ‫it receives a callback function. 51 00:02:22,500 --> 00:02:25,130 ‫And all we're gonna do is to write 52 00:02:27,720 --> 00:02:31,440 ‫immediate one finished, and this one doesn't have 53 00:02:31,440 --> 00:02:33,520 ‫any time, because it's not necessary 54 00:02:33,520 --> 00:02:36,930 ‫because as the name says, it is immediate. 55 00:02:36,930 --> 00:02:38,540 ‫Then another thing that we want to do 56 00:02:38,540 --> 00:02:41,620 ‫is to read this file here, and then pass 57 00:02:41,620 --> 00:02:44,930 ‫a callback function, okay, so the first thing 58 00:02:44,930 --> 00:02:48,963 ‫is that we have to require the correct module, so FS, 59 00:02:52,600 --> 00:02:54,987 ‫and now fs.readFile, and we want text-file.txt, 60 00:03:05,586 --> 00:03:08,003 ‫and then something to happen. 61 00:03:09,270 --> 00:03:12,153 ‫And just like before, let's just say here, 62 00:03:13,740 --> 00:03:17,263 ‫in this case I/O finished, alright. 63 00:03:18,830 --> 00:03:21,170 ‫So I/O because this callback here 64 00:03:21,170 --> 00:03:24,830 ‫is actually related to a I/O task, 65 00:03:24,830 --> 00:03:28,440 ‫which actually gets it's own phase in the event loop, right. 66 00:03:28,440 --> 00:03:31,930 ‫And then finally, let's just add a console.log here, 67 00:03:31,930 --> 00:03:35,473 ‫saying well, hello from the top level code. 68 00:03:37,517 --> 00:03:40,440 ‫Okay, and so top level code, because it's actually 69 00:03:40,440 --> 00:03:43,130 ‫the only one that is not inside of any callback. 70 00:03:43,130 --> 00:03:46,000 ‫So in this very small example that we have for now, 71 00:03:46,000 --> 00:03:48,400 ‫let's try to figure out what should happen first. 72 00:03:48,400 --> 00:03:50,510 ‫Well, remember that the first step 73 00:03:50,510 --> 00:03:53,310 ‫when we load a module is that it's top level code 74 00:03:53,310 --> 00:03:56,000 ‫gets executed, so right away we should see 75 00:03:56,000 --> 00:03:59,360 ‫this console.log here, right, only then later 76 00:03:59,360 --> 00:04:02,110 ‫we should see the other logs coming from 77 00:04:02,110 --> 00:04:04,280 ‫these other callbacks, because these callbacks 78 00:04:04,280 --> 00:04:06,820 ‫will actually run in the event loop. 79 00:04:06,820 --> 00:04:09,190 ‫So let's try to see if that's actually the case, 80 00:04:09,190 --> 00:04:12,000 ‫and then analyze it a bit better even. 81 00:04:12,000 --> 00:04:15,150 ‫So opening up the console here, and again, 82 00:04:15,150 --> 00:04:17,250 ‫I'm doing that by using terminal, 83 00:04:17,250 --> 00:04:22,023 ‫or actually in the view, so this terminal here, alright. 84 00:04:23,100 --> 00:04:27,020 ‫So note, event-loop.js, or actually 85 00:04:27,020 --> 00:04:30,960 ‫before we do so, I need to fix this typo here, 86 00:04:30,960 --> 00:04:33,580 ‫so it's test file, not text file. 87 00:04:33,580 --> 00:04:36,093 ‫Okay, but now we're ready to run this command, 88 00:04:36,960 --> 00:04:40,320 ‫and the results are in, so the first log 89 00:04:40,320 --> 00:04:43,810 ‫that we have here is hello from the top level code, 90 00:04:43,810 --> 00:04:46,100 ‫and that was expected, right, because 91 00:04:46,100 --> 00:04:49,390 ‫this is a code that gets executed immediately. 92 00:04:49,390 --> 00:04:52,940 ‫Then after that, we have these three outputs, 93 00:04:52,940 --> 00:04:55,460 ‫but they are actually in no particular order, 94 00:04:55,460 --> 00:04:57,640 ‫and that's because this code here, 95 00:04:57,640 --> 00:05:00,970 ‫so this code, is actually not in an I/O cycle, 96 00:05:00,970 --> 00:05:03,780 ‫so it's not running inside of the event loop, 97 00:05:03,780 --> 00:05:07,170 ‫because it's not running inside of any callback function. 98 00:05:07,170 --> 00:05:10,370 ‫Okay, so in your computer, you might actually see 99 00:05:11,470 --> 00:05:13,160 ‫this log here before this one, 100 00:05:13,160 --> 00:05:15,360 ‫and then this one here is only the last one 101 00:05:15,360 --> 00:05:18,550 ‫because this kind of big file here 102 00:05:18,550 --> 00:05:20,840 ‫takes some time to read, and so it's 103 00:05:20,840 --> 00:05:23,060 ‫probably always gonna be the last one. 104 00:05:23,060 --> 00:05:27,140 ‫So again, at this point, the order of these three here 105 00:05:27,140 --> 00:05:29,640 ‫doesn't have anything to do with the event loop, 106 00:05:29,640 --> 00:05:31,320 ‫because they're actually not running 107 00:05:31,320 --> 00:05:33,420 ‫inside the event loop just yet. 108 00:05:33,420 --> 00:05:36,490 ‫For that, we will have to move them, 109 00:05:36,490 --> 00:05:40,490 ‫or at least move these two here, inside a callback function. 110 00:05:40,490 --> 00:05:43,713 ‫And so, for that we're gonna use this one here actually. 111 00:05:45,270 --> 00:05:50,190 ‫So let me put it here, and say timer two and timer two here, 112 00:05:50,190 --> 00:05:55,190 ‫or immediate two, and I'm also gonna add another timer here, 113 00:05:55,270 --> 00:05:57,740 ‫so timer three, and this one is gonna run 114 00:05:57,740 --> 00:06:01,140 ‫for three seconds, so that is 3000 milliseconds. 115 00:06:01,140 --> 00:06:03,840 ‫So let's now try the result of this one. 116 00:06:03,840 --> 00:06:06,230 ‫But before we do that, let's actually think 117 00:06:06,230 --> 00:06:09,660 ‫why right after all the code before had run, 118 00:06:09,660 --> 00:06:13,730 ‫the program then exited and went back to the prompt here. 119 00:06:13,730 --> 00:06:16,500 ‫So remember how Node.js decides if it should continue 120 00:06:16,500 --> 00:06:19,000 ‫running the event loop, well it does so 121 00:06:19,000 --> 00:06:21,620 ‫by asking if there is still any time running 122 00:06:21,620 --> 00:06:24,580 ‫in the background, and if so, it will not finish, 123 00:06:24,580 --> 00:06:26,800 ‫and if there is still a pending timer, 124 00:06:26,800 --> 00:06:29,140 ‫well then it's not gonna exit the program. 125 00:06:29,140 --> 00:06:30,920 ‫But if there's not, which was the case 126 00:06:30,920 --> 00:06:33,920 ‫in the first example here, then it immediately 127 00:06:33,920 --> 00:06:36,660 ‫exits the program, okay, but now we actually 128 00:06:36,660 --> 00:06:38,980 ‫have one timer here, so this one will run 129 00:06:38,980 --> 00:06:41,620 ‫for three seconds, and so let's try 130 00:06:41,620 --> 00:06:43,220 ‫to figure out what happens here. 131 00:06:45,260 --> 00:06:47,450 ‫Okay, so you see that it's not exiting, 132 00:06:47,450 --> 00:06:50,640 ‫and only now, after timer three has finished, 133 00:06:50,640 --> 00:06:53,170 ‫it did then exit the application. 134 00:06:53,170 --> 00:06:56,100 ‫Okay, so let's actually just see that again, 135 00:06:56,100 --> 00:06:59,480 ‫so all these logs timers running, timer finished, 136 00:06:59,480 --> 00:07:02,070 ‫and so it exited the application. 137 00:07:02,070 --> 00:07:04,490 ‫Now about these results here, let's actually make 138 00:07:04,490 --> 00:07:06,820 ‫this here a bit easier to see, 139 00:07:06,820 --> 00:07:10,113 ‫and add just a small separator here. 140 00:07:11,360 --> 00:07:14,683 ‫Okay, clean this, okay. 141 00:07:16,510 --> 00:07:19,600 ‫So these four ones here are the outputs 142 00:07:19,600 --> 00:07:22,110 ‫that were not really running in the event loop, 143 00:07:22,110 --> 00:07:24,380 ‫but these three here were actually coming 144 00:07:24,380 --> 00:07:28,150 ‫out of the event loop, so let's now analyze these results. 145 00:07:28,150 --> 00:07:29,980 ‫Now, if you'll remember the diagram 146 00:07:29,980 --> 00:07:32,690 ‫from the previous lecture, you will probably have thought 147 00:07:32,690 --> 00:07:36,960 ‫that the timer, so timer two here, 148 00:07:36,960 --> 00:07:39,640 ‫should actually finish before the setImmediate, 149 00:07:39,640 --> 00:07:42,640 ‫because in the diagram, it actually appeared first 150 00:07:42,640 --> 00:07:45,100 ‫right at the top of the event loop. 151 00:07:45,100 --> 00:07:48,090 ‫So we have to set timeout here with zero, 152 00:07:48,090 --> 00:07:52,500 ‫which should kind of be the same as setImmediate, right. 153 00:07:52,500 --> 00:07:54,610 ‫So why does setImmediate actually 154 00:07:54,610 --> 00:07:57,630 ‫appear before the setTimeout? 155 00:07:57,630 --> 00:08:00,020 ‫Well, there's something that I didn't really explain 156 00:08:00,020 --> 00:08:02,470 ‫in the last video, because I didn't want to make it 157 00:08:02,470 --> 00:08:05,750 ‫even more confusing, and that is that the event loop 158 00:08:05,750 --> 00:08:09,320 ‫actually waits for stuff to happen in the poll phase. 159 00:08:09,320 --> 00:08:12,270 ‫So in that phase where I/O callbacks are handled. 160 00:08:12,270 --> 00:08:15,400 ‫So when this queue of callbacks is empty, 161 00:08:15,400 --> 00:08:17,940 ‫which is the case in our fictional example here, 162 00:08:17,940 --> 00:08:20,270 ‫so we have no I/O callbacks, all we have 163 00:08:20,270 --> 00:08:23,500 ‫is these timers, well then the event loop 164 00:08:23,500 --> 00:08:27,490 ‫will wait in this phase until there is an expired timer. 165 00:08:27,490 --> 00:08:31,430 ‫But, if we scheduled a callback using setImmediate, 166 00:08:31,430 --> 00:08:34,320 ‫then that callback will actually be executed 167 00:08:34,320 --> 00:08:36,920 ‫right away after the polling phase, 168 00:08:36,920 --> 00:08:40,240 ‫and even before expired timers, if there is one. 169 00:08:40,240 --> 00:08:43,270 ‫And in this case, the timer expires right away, 170 00:08:43,270 --> 00:08:46,080 ‫so after zero seconds, but again, the event loop 171 00:08:46,080 --> 00:08:49,710 ‫actually waits, so it pauses in the polling phase. 172 00:08:49,710 --> 00:08:52,100 ‫And so that setImmediate callback 173 00:08:52,100 --> 00:08:55,580 ‫is actually executed first, so that is the whole reason 174 00:08:55,580 --> 00:08:59,730 ‫why we have this immediate here after we have the timers. 175 00:08:59,730 --> 00:09:02,770 ‫Okay, and I know this sounds very confusing, 176 00:09:02,770 --> 00:09:04,810 ‫and I completely agree, but really 177 00:09:04,810 --> 00:09:08,090 ‫that's just the way Node.js works. 178 00:09:08,090 --> 00:09:11,380 ‫And now let's make this even a little bit more confusing, 179 00:09:11,380 --> 00:09:14,250 ‫and add the process.nextTick that 180 00:09:14,250 --> 00:09:16,950 ‫we talked about also in the last lecture. 181 00:09:16,950 --> 00:09:21,950 ‫So we say process.nextTick, and then just like before, 182 00:09:22,170 --> 00:09:24,323 ‫we simply pass it a callback function. 183 00:09:25,540 --> 00:09:27,640 ‫And again, I just wanna log to console, 184 00:09:27,640 --> 00:09:31,663 ‫and I'm gonna say process.nextTick. 185 00:09:32,550 --> 00:09:36,150 ‫So what do you think will happen in this case? 186 00:09:36,150 --> 00:09:40,170 ‫Go ahead and make a guess, and once you're ready 187 00:09:40,170 --> 00:09:42,883 ‫you can then run this, so let's do that. 188 00:09:44,120 --> 00:09:48,280 ‫Save it here first, run it, and so here we go. 189 00:09:48,280 --> 00:09:51,760 ‫So the results are again in, and now the first callback 190 00:09:51,760 --> 00:09:55,640 ‫that was executed was actually this function here. 191 00:09:55,640 --> 00:09:58,220 ‫So that's why we have process.nextTick 192 00:09:58,220 --> 00:09:59,710 ‫right in the first one. 193 00:09:59,710 --> 00:10:03,500 ‫So why was this callback function of process.nextTick 194 00:10:03,500 --> 00:10:06,570 ‫the first one of all of them to be executed? 195 00:10:06,570 --> 00:10:09,070 ‫Well, remember that nextTick is part 196 00:10:09,070 --> 00:10:12,410 ‫of the microtasks queue, which get executed 197 00:10:12,410 --> 00:10:16,530 ‫after each phase, so not just after one entire tick. 198 00:10:16,530 --> 00:10:19,120 ‫And so what happened here is that this callback function 199 00:10:19,120 --> 00:10:23,660 ‫actually ran before the phase where this callback function 200 00:10:23,660 --> 00:10:26,970 ‫here ran, and the phase before that, okay. 201 00:10:26,970 --> 00:10:30,850 ‫Now nextTick is actually really a misleading name, 202 00:10:30,850 --> 00:10:33,990 ‫because a tick is actually an entire loop, 203 00:10:33,990 --> 00:10:37,860 ‫but nextTick actually happens before the next loop phase, 204 00:10:37,860 --> 00:10:41,990 ‫and not the entire tick, so that's what I was saying before. 205 00:10:41,990 --> 00:10:45,830 ‫Then on the other side, setImmediate would make you think 206 00:10:45,830 --> 00:10:49,690 ‫that it's callback would be executed immediately, 207 00:10:49,690 --> 00:10:52,780 ‫but it actually doesn't, right, so setImmediate 208 00:10:52,780 --> 00:10:55,570 ‫actually gets executed once per tick, 209 00:10:55,570 --> 00:10:58,800 ‫while nextTick gets executed immediately. 210 00:10:58,800 --> 00:11:01,820 ‫And so their two names should actually be switched. 211 00:11:01,820 --> 00:11:03,700 ‫They should be the other way around, 212 00:11:03,700 --> 00:11:05,390 ‫and this can cause a lot of confusion, 213 00:11:05,390 --> 00:11:08,440 ‫so it's best to just always stick to one of them, 214 00:11:08,440 --> 00:11:12,470 ‫and that's usually setImmediate and not process.nextTick. 215 00:11:12,470 --> 00:11:15,070 ‫Now anyway, as I mentioned in a last video, 216 00:11:15,070 --> 00:11:18,530 ‫these mechanisms are actually more for pretty advanced 217 00:11:18,530 --> 00:11:20,320 ‫use cases, which is why we will 218 00:11:20,320 --> 00:11:22,760 ‫probably not use them in our project. 219 00:11:22,760 --> 00:11:24,970 ‫But if you want to learn more about them, 220 00:11:24,970 --> 00:11:28,060 ‫you can always read the official Node documentation. 221 00:11:28,060 --> 00:11:30,660 ‫Okay, so with this we have simulated 222 00:11:30,660 --> 00:11:33,250 ‫some aspects of the event loop, 223 00:11:33,250 --> 00:11:35,500 ‫but to finish, I want to just quickly 224 00:11:35,500 --> 00:11:38,290 ‫introduce something about thread pool as well, 225 00:11:38,290 --> 00:11:40,950 ‫and for that we're gonna do a more complex operation 226 00:11:40,950 --> 00:11:43,490 ‫that will actually be offloaded to the thread pool, 227 00:11:43,490 --> 00:11:47,040 ‫and take a look at how long these operations take to run, 228 00:11:47,040 --> 00:11:48,510 ‫and how we can change the thread pool 229 00:11:48,510 --> 00:11:50,870 ‫size that we talked about before. 230 00:11:50,870 --> 00:11:52,840 ‫So we're gonna use some cryptography here 231 00:11:52,840 --> 00:11:55,203 ‫to basically encrypt a password. 232 00:11:58,620 --> 00:12:00,820 ‫So that's a new package we hadn't used before, 233 00:12:00,820 --> 00:12:04,130 ‫and it's called Crypto, but I mentioned earlier 234 00:12:04,130 --> 00:12:07,063 ‫that actually, all the functions from this package, 235 00:12:07,960 --> 00:12:11,260 ‫they will be offloaded automatically by the event loop 236 00:12:11,260 --> 00:12:13,280 ‫to the thread pool, and so that's 237 00:12:13,280 --> 00:12:14,780 ‫what we're gonna test out now. 238 00:12:18,380 --> 00:12:22,070 ‫And let's use this now, so crypto.pb, 239 00:12:22,070 --> 00:12:25,303 ‫so we're gonna use an encryption function called pbkdf2, 240 00:12:27,610 --> 00:12:31,050 ‫so kind of a weird name, and now we pass in 241 00:12:31,050 --> 00:12:34,640 ‫the secret string, which let's just say password, 242 00:12:34,640 --> 00:12:37,520 ‫then we need a string to solve the passwords, 243 00:12:37,520 --> 00:12:40,820 ‫and the implementations here don't really matter, 244 00:12:40,820 --> 00:12:42,970 ‫so for now I'm not gonna go into any detail 245 00:12:42,970 --> 00:12:46,150 ‫of how this works, we're gonna do that later, okay, 246 00:12:46,150 --> 00:12:48,320 ‫so here we just need the key length, 247 00:12:48,320 --> 00:12:50,070 ‫so this number here is just for the number 248 00:12:50,070 --> 00:12:53,870 ‫of iterations, then this is the key length, 249 00:12:53,870 --> 00:12:56,020 ‫and then finally the algorithm, 250 00:12:56,020 --> 00:12:58,430 ‫which is gonna be used to encrypt the password. 251 00:12:58,430 --> 00:13:00,380 ‫So these numbers will simply increase 252 00:13:00,380 --> 00:13:02,483 ‫the time it takes for the encryption. 253 00:13:04,970 --> 00:13:08,610 ‫Okay and then finally, it also takes a callback function, 254 00:13:08,610 --> 00:13:11,483 ‫and all I'm gonna do here is to do another console.log, 255 00:13:12,730 --> 00:13:16,453 ‫and just say password encrypted. 256 00:13:17,950 --> 00:13:20,740 ‫Now, for the purpose of this demonstration, 257 00:13:20,740 --> 00:13:24,220 ‫I actually want to show you how much time 258 00:13:24,220 --> 00:13:27,400 ‫each of these operations take, so what we're gonna do 259 00:13:27,400 --> 00:13:32,010 ‫is to basically define a variable in the beginning, 260 00:13:32,010 --> 00:13:37,010 ‫set it to date.now, so that is the current date 261 00:13:37,120 --> 00:13:41,310 ‫in milliseconds, and then here, all we have to do 262 00:13:41,310 --> 00:13:46,310 ‫is to log not only the string, but also date.now, 263 00:13:46,310 --> 00:13:49,700 ‫which will be the date at this point in milliseconds, 264 00:13:49,700 --> 00:13:53,010 ‫minus the start, and so that will then give us 265 00:13:53,010 --> 00:13:55,380 ‫the amount of milliseconds that have passed 266 00:13:55,380 --> 00:13:57,380 ‫in order to do this calculation. 267 00:13:57,380 --> 00:13:59,693 ‫Okay, so let's try it out, give it a save, 268 00:14:00,890 --> 00:14:05,360 ‫and run it again, and so here you see 269 00:14:05,360 --> 00:14:08,530 ‫that it took 1855 milliseconds, 270 00:14:08,530 --> 00:14:12,250 ‫so almost two seconds to encrypt this password. 271 00:14:12,250 --> 00:14:15,110 ‫Okay, but now let's actually duplicate 272 00:14:15,110 --> 00:14:17,360 ‫this code, or actually I want four instances 273 00:14:17,360 --> 00:14:19,660 ‫of this to show you something. 274 00:14:19,660 --> 00:14:23,400 ‫So if we run this now, it should probably take 275 00:14:23,400 --> 00:14:25,710 ‫approximately the same amount of time, 276 00:14:25,710 --> 00:14:27,980 ‫and yeah it does, so it was 1.8 seconds, 277 00:14:27,980 --> 00:14:31,620 ‫now it's 2.2 seconds, which is quite similar. 278 00:14:31,620 --> 00:14:34,530 ‫Okay, and remember that I told you in one of 279 00:14:34,530 --> 00:14:36,630 ‫the earlier lectures, that by default 280 00:14:36,630 --> 00:14:39,360 ‫the size of the thread pool is four, 281 00:14:39,360 --> 00:14:41,720 ‫so there are four threads doing the work 282 00:14:41,720 --> 00:14:44,010 ‫at the same time, and so that's why 283 00:14:44,010 --> 00:14:46,160 ‫these four password encryptions 284 00:14:46,160 --> 00:14:48,000 ‫take approximately the same time 285 00:14:48,000 --> 00:14:50,740 ‫and happen basically all at the same time. 286 00:14:50,740 --> 00:14:53,990 ‫But we can actually change that thread pool size. 287 00:14:53,990 --> 00:14:57,100 ‫So, let me show you how we do that, 288 00:14:57,100 --> 00:14:59,867 ‫and we do that by saying process.env, 289 00:15:01,290 --> 00:15:03,230 ‫and that's an environmental variable, 290 00:15:03,230 --> 00:15:05,680 ‫and again we're gonna talk more about that later, 291 00:15:06,684 --> 00:15:08,613 ‫and UV, which stands for LibUV, 292 00:15:11,232 --> 00:15:15,500 ‫threadpool size, so if we set this to one, 293 00:15:15,500 --> 00:15:18,783 ‫we will only have one thread in our thread pool. 294 00:15:21,110 --> 00:15:26,110 ‫So let's try that again, and so let's see what happens now. 295 00:15:28,650 --> 00:15:32,840 ‫So you see that they all take much longer to calculate. 296 00:15:32,840 --> 00:15:35,490 ‫Basically, they are calculated one after the other. 297 00:15:35,490 --> 00:15:38,470 ‫So this one the first, then this one here takes 298 00:15:38,470 --> 00:15:40,610 ‫double the time, and again that's because 299 00:15:40,610 --> 00:15:42,980 ‫this one can only start as soon as 300 00:15:42,980 --> 00:15:45,160 ‫the first one is completed, and the same 301 00:15:45,160 --> 00:15:46,893 ‫with the third and the fourth one. 302 00:15:47,920 --> 00:15:49,620 ‫Now let's say we change it to two, 303 00:15:52,170 --> 00:15:54,300 ‫then we should see the first two ones 304 00:15:54,300 --> 00:15:56,990 ‫with the same time, and exactly, 305 00:15:56,990 --> 00:15:59,710 ‫the second two also with a similar time. 306 00:15:59,710 --> 00:16:01,363 ‫So that makes sense, right. 307 00:16:02,650 --> 00:16:04,500 ‫Just for the sake of completion here, 308 00:16:05,610 --> 00:16:08,950 ‫now the same with three, so these three 309 00:16:08,950 --> 00:16:11,340 ‫have a similar time, and then the last one. 310 00:16:11,340 --> 00:16:15,440 ‫Alright, so this is how the thread pool works basically, 311 00:16:15,440 --> 00:16:18,660 ‫so I decided to not only focus on the event loop, 312 00:16:18,660 --> 00:16:22,630 ‫but also to give you an overview, a very quick one, 313 00:16:22,630 --> 00:16:25,010 ‫of the thread pool and how we can change 314 00:16:25,010 --> 00:16:27,620 ‫the thread pool size, okay, keep in mind 315 00:16:27,620 --> 00:16:29,560 ‫that this code here is actually still 316 00:16:29,560 --> 00:16:33,230 ‫asynchronous, because we passed in a callback function. 317 00:16:33,230 --> 00:16:36,490 ‫Okay, and we could actually use the synchronous version, 318 00:16:36,490 --> 00:16:38,920 ‫but that would then block the event loop. 319 00:16:38,920 --> 00:16:40,650 ‫Wanna see that? 320 00:16:40,650 --> 00:16:43,183 ‫So let me very quickly show that to you as well, 321 00:16:44,120 --> 00:16:46,130 ‫so that one was not really planned, 322 00:16:46,130 --> 00:16:48,240 ‫but let's do it anyway, 'cause it's 323 00:16:48,240 --> 00:16:50,090 ‫very interesting to see that I think. 324 00:16:51,580 --> 00:16:53,830 ‫Okay, so that will work like this. 325 00:16:53,830 --> 00:16:57,570 ‫We use again the sync version of the same function, 326 00:16:57,570 --> 00:16:59,950 ‫which a note, is many times available. 327 00:16:59,950 --> 00:17:02,760 ‫Remember we have the same for the read file, 328 00:17:02,760 --> 00:17:05,190 ‫so we have read file, which accepts a callback, 329 00:17:05,190 --> 00:17:08,290 ‫and we have read file sync, which is the synchronous version 330 00:17:08,290 --> 00:17:11,440 ‫which doesn't accept any callback, so just like this. 331 00:17:11,440 --> 00:17:13,520 ‫So this one will then encrypt the password, 332 00:17:13,520 --> 00:17:16,890 ‫block the code execution, and then move on to the next line, 333 00:17:16,890 --> 00:17:19,700 ‫which will then log this here to the console. 334 00:17:19,700 --> 00:17:21,823 ‫So let's now duplicate this here. 335 00:17:23,570 --> 00:17:26,553 ‫That was too much, get rid of this one here, 336 00:17:27,500 --> 00:17:31,310 ‫and so now these four password encryptions 337 00:17:31,310 --> 00:17:33,350 ‫will no longer run in the event loop. 338 00:17:33,350 --> 00:17:37,070 ‫And so they will no longer be offloaded to the thread pool. 339 00:17:37,070 --> 00:17:39,980 ‫Okay, and so now even if we have the thread pool size 340 00:17:39,980 --> 00:17:42,583 ‫of four, let's see what happens. 341 00:17:46,010 --> 00:17:50,080 ‫So you see, they happen completely in a synchronous way. 342 00:17:50,080 --> 00:17:53,290 ‫So one after the other, and what is even worse, 343 00:17:53,290 --> 00:17:55,350 ‫is that all of these timers here, 344 00:17:55,350 --> 00:17:57,960 ‫even nextTick and the immediate one, 345 00:17:57,960 --> 00:18:01,850 ‫only appeared after the password encryptions happened. 346 00:18:01,850 --> 00:18:04,990 ‫So this really was blocking the entire execution, 347 00:18:04,990 --> 00:18:07,460 ‫even if this timer here, for example this one here, 348 00:18:07,460 --> 00:18:09,580 ‫was finished after zero seconds, 349 00:18:09,580 --> 00:18:11,440 ‫and this one after three seconds, 350 00:18:11,440 --> 00:18:13,830 ‫but they all have to wait seven seconds 351 00:18:13,830 --> 00:18:16,010 ‫until all of these password encryptions here 352 00:18:16,010 --> 00:18:19,670 ‫were finally ready, again because they were not running 353 00:18:19,670 --> 00:18:22,120 ‫inside the event loop, but these were. 354 00:18:22,120 --> 00:18:24,960 ‫And so they were basically working in the background 355 00:18:24,960 --> 00:18:26,890 ‫and could only be picked up by the event loop 356 00:18:26,890 --> 00:18:29,470 ‫when they were ready, right after these four 357 00:18:29,470 --> 00:18:32,110 ‫password encryptions, so this one was 358 00:18:32,110 --> 00:18:34,760 ‫another great example of seeing the 359 00:18:34,760 --> 00:18:38,240 ‫code blocking and event loop all in action. 360 00:18:38,240 --> 00:18:41,600 ‫Okay, so that was enough for one lecture, 361 00:18:41,600 --> 00:18:43,270 ‫I hope that you found it interesting, 362 00:18:43,270 --> 00:18:45,220 ‫and I'll see you right in the next one.