Communicating between processes (using pipes) in C

[@jayshah8843]

why you don't use wait in parent process(else part) because both process are running parallel

[@CodeVault]

You're right, I think a wait(NULL) is missing at the end of the else part. Although, since, we're writing from the child process to the parent, the program will work properly albeit with some resource leaks. I'm glad you actually noticed my mistake. Good job!

[@lxw5231]

I dont understand， why there is resource leak without wait(NULL)?

[@AyushAnshul]

@@CodeVault Why doesn't parent end while we are waiting for input in child?

[@Jason-lb1lu]

@@lxw5231 because the parent might finish before the child process, which will result in the child process becoming a zombie process, ie its data is not cleared by the time you program ends, taking up space in your system while doing nothing hence a zombie process

[@josephmasinre1840]

@@CodeVault I don't think wait(NULL) is needed, since read is a blocking call, the child will wait until the parent writes into the pipe.

[@morpheus7422]

Why is channel underrated, I love how you explain just so much.. stuff that took me weeks to grasp just in one video. I wish I found you earlier

[@californiacrunchmuffin2918]

As a CS student I’ve watched countless tutorials and you are by far one of (if not) the best instructors I’ve come across

[@patrickbitzer8350]

any further recommendations for c? 😇

[@californiacrunchmuffin2918]

@@patrickbitzer8350 Not necessarily C, but for C++ Cherno has really good videos for understanding fundamentals

[@nicofernandez865]

dude, all tour videos from the playlist which includes this video have helped a lot in university. thank you so much and keep it up!

[@SlowedOutOfExistence]

you're a legend you should be proud

[@NavyEagle1]

No word can describe how much your videos helped me take my C a step fourther. Thank youuu 🙏❤

[@ryoma8402]

Your videos are excellent. Really helpful to all IT students out there. Short and straight to the point. And since they explain the basics of every subject so well the rest of the studying is easily done. Keep up the good work.

[@shawnl1155]

Wow, this is the most clear and concise coding lessons I have found on youtube. Perfect pace, audio and video quality is great, everything clear. Thank you so much. I was thinking of dropping my university OS course but now I think I may be able to pass with your videos.

[@johndoesson]

I've been watching your videos, like how you take the time to explain things which might not always be so obvious. You are the only one who has (good) tutorials on IPC, coulnd't find any other, thought I was lucky when I saw you made two videos on IPC but then checked your channel and saw you've not only covered looots of IPC but also have a huge library of videos on C. So surprising due to how little views/subs you have, very underrated. I must ask, I tried to setup the IDE you use, visual studio code and couldn't get it to run a program, tried looking up how to do it but couldn't find anything clear on it for ubuntu, seems rather advanced to set it up so everything works smoothly? Spent the whole day looking for a good IDE, tried Clion, which froze upon loading project and geany which was no better than texteditor imo :/

[@CodeVault]

Thank you! I have a video on how to set it up on Windows, although it should be the exact same setup for Linux. You just hate to point VSCode to gcc instead of mingw. If it's still an issue, you can send me a message over on Discord and I'll send you the exact configurations I have for Linux.

[@abolevi3768]

your video is 4 years old but I really appreciate your help

[@chenruzhao6440]

Thank you so much for making and posting the Unix Processes in C series of videos, it helps me a lot !!!

[@nicholasfoster5065]

This video just saved me 2 hours of reading explaining what should be a simple concept. Thank you so much =D

[@LamNguyen-jp5vh]

Thank you so much for recording this video! I have an OS class at school and the professor never taught us anything about this. Then he just released a project and I was hopeless until found this video!

[@tomasglavina4166]

You are amazing and an amazing teacher, the way you explain is so clear and concise. 15 min of your videos is about a month or two of school classes. You deserve AT LEAST 150k subs

[@harshdeepgupta]

This is amazing! What my professors never taught, it is explained here so succinctly. Thank you for making this video!

[@abhinavsharma1075]

Not all heroes wear capes...Some make useful tutorial tooo ... thanx buddy!!!

[@eylulgunes0289]

youtube's best c narrator 👑👑

[@JYSERroshanseeam]

Thank you so much, i wish my professors explained this well

[@Burak-cr6um]

It was really helpful, thank you. A complex concept can only be simplified in this way.

[@abbashaider7165]

You have clear concepts with nice articulating skills. Thankyou :)

[@blazkowicz666]

You're doing God's work 🙏🙏 💯

[@deli5777]

Thanks! I spend hours trying to figure out my problem before finding this video and fixed with a few minutes of starting

[@habibhasanshakil9086]

Awesome videos no doubt. This playlist is the lifeline of my OS labs this semester. I have one suggestion for you; it would be better if you use an online board and some diagrams when explaining codes. Though I understood most of the explanations, I recommended this playlist to one of my friends and he didn't understand many things. not everyone has good imagination skills. Subscribed your channel. God bless you.

[@CodeVault]

Thanks for the suggestion! I will keep it in mind for the future videos

[@mrtom-a-hawk6732]

You literally saved my lab grade! Thank you so much for this very clear tutorial!

[@cinematicShorts000]

I haven't understood forks and pipes all semester, but these two videos that you have were very well explained! Thank you so much, I might just pass my exam lol

[@sergi9405]

00:00 - Introduction to inter-process communication and the purpose of the video. 01:20 - Explanation of pipes as a method of inter-process communication. 02:40 - Basic syntax and functions for creating pipes in C. 04:15 - Demonstration of creating a pipe in C with a simple example. 06:00 - Discussion of reading from and writing to pipes. 07:30 - Example of parent-child process communication using pipes. 10:00 - Handling errors and closing pipes. 12:00 - Summary and conclusion.

[@maryreilly5102]

You're an amazing teacher... and cute ha! Thanks for the tutorials!!!!

[@CodeVault]

Wow, thanks! Feel free to join our discord community if you have anything you want to talk about: discord.code-vault.net

[@aniketpalve6615]

Good Explanation... Really helps to solve the college assignments solution.

[@aimenigh4413]

Thank you very much sir , you have a very good explication , thanks a lot from Algeria ❤️

[@Squish888]

Your videos are a massive help!

[@Alpha-ng6oc]

You're explaining that very clearly. Thank you, it helped me very much!

[@dr-mee]

You are legend man.

[@murilo_dev]

Very nice explanation! Thank you very much for your content!

[@haster6400]

THis is one of the best video that I had liked Thanks you very much

[@enkelly7496]

Absolutely love this content, thank you!!

[@back81192]

Man, you are my savior!

[@mohansuri2683]

Thanks a ton for this video, This cleared up so many things to me

[@bama2619]

great teaching skills, thank you. Understandable after watching for the first time.))

[@kewtomrao]

These vids are damn helpful for my OS practical classes.Is there a video where you show how you set up vs code and the debugger for C?I use sublime text now but without debugger.Thanks

[@CodeVault]

This one: code-vault.net/course/yx1g2sh6l4:1610029046575/lesson/4wy66ezt7u:1610303902122 And the next in the playlist shows how to run in on Linux and how I actually run VSCode

[@jeroen3648]

Thank you for this tutorial, it helped me understand linux pipe :)

[@fernandoguirao3748]

Super clear video! Do you have any extension for VS to show a little explanation of the functions when you have your cursor above?, when I do so it only shows me the prototype of the function

[@CodeVault]

I have the C/C++ extension from Microsoft. It should work but you just have to make sure it's configured correctly (there might be some path you have to add to the headers and whatnot)

[@danielmouraJC]

Me too

[@kagaskaa2680]

​@@CodeVault can u please elaborate because installing the extension is easy but I have no idea how to configure it, as a beginner this information pop-up can help us a lot!

[@danielmouraJC]

@@CodeVault I haven't been able to

[@isakarahan3037]

You are awesome, I really understood the topic with your explanations. Thanks you so much....

[@vivekkumarverma685]

Well explained... Simply amazing 🤩

[@Yuri-bt4wl]

You sound just like Shaggy lol Thank you for the lesson!

[@mushroom2493]

thanks for the video. you saved me. I love you. hope you have a good life :')

[@keithdumont]

Love your videos, thank you!!

[@oleholgerson3416]

Thank you for sharing your knowledge, that was very helpful

[@xinking2644]

thanks for your video! What should I do if I want to get some complex return value like array of class object from child process ?

[@CodeVault]

Here's a video on how to send an array through pipes: code-vault.net/lesson/phac6gv4cy:1603733529763 It's very similar to how you would send a struct or object

[@xinking2644]

@@CodeVault get it , thank you!

[@jonathanazzopardipaul5048]

Great video, understand pipes now. Cheers!

[@nobi_nose9469]

you are amazing. thank you for making this video!

[@gustavoalexguardiaguardia5790]

quality content! What book would you recommend reading about operating system?

[@CodeVault]

Just the up-to-date manual on any operating system has enough information. Books could be outdated and I never really look into them

[@StackMemory0x00]

The best book you could ever read about programming and OS is Computer Science from bottom up for Ian Wienand. Its a great book by all means. You will never regret any minutes spent reading. I wish if I found this book years ago.

[@sarahali6946]

thank you this was really helpful and it saved me a lot of time

[@coreytodtaylor]

Hey! I like your videos! The only thing I suppose was wrong in that one is that your doesn't close the descriptor in case of write or read error and return straight away

[@CodeVault]

Yep, in production environments it is recommended to check for those errors. Here I don't because it would distract from the main concept and a lot of the time it's difficult to force an error to exemplify what the code does

[@moizcrafts3893]

this seem to me impossible while studying in uni,but now u have explained it really good

[@benwolio9356]

great lesson hairline man

[@vkatasonov]

Hello and thx for the video. One thing that confused me a little bit is why do we close fd before making some operation. It seems to be more logical if pipe would read from fd0 and then write to fd1. But looks like it’s two different processes.

[@vkatasonov]

If you close fd in one process in another it will still work?

[@CodeVault]

fds are duplicated after you call fork(). So, if you open a pipe() and then fork() you have 4 fds in total. Since from one process we only read and from another we only write we don't need half of them

[@vaibhavpanvalkar3025]

@CodeVault has real value

[@uwu-zx5hv]

you explain better and faster than my teacher jsdksjd thank you

[@alternativeenergyresearch4857]

Make video on how to make Excel as dde server so that every second data in Excel may be poke out to trading platform or charting software

[@jamshidbek2000]

Thanks for the explanation. QUESTION : if there is an error when you either read or write and return the program, Will the file descriptors be left open?

[@CodeVault]

Once the program finsihes execution, the operating system should automatically close those file descriptors

[@jamshidbek2000]

@@CodeVault Thank you =)

[@ahmedf2]

Thanks a lot for the wonderful video, I have a question, why do we need to communicate between processes?

[@CodeVault]

There are a lot of reasons. Think about all the tools you're using on your computer and what happens when you do something that makes them interact. Something like, drag and dropping an image from a process to another Other reasons could be to reuse functionality. If you have a program and you want to count the number of words in some text you could reuse the program "wc" and simply put a pipe between your process and the "wc" process' stdin and stdout

[@ahmedf2]

@@CodeVault Thanks a lot my friend, by the way what's your name?

[@joanbo2346]

Really helpfull explanation and example. Many thanks dude :D

[@hackedyou116]

@CodeVault , why cant we use a global valiable in that program declared before fork() and just store the input value in that variable?

[@CodeVault]

Because global variables are only global to the process. Each process (child and parent process) get their own set of global variables. Modifying one global variable in one process won't change it in the other

[@exeprinced]

Excellent tutorial. Thanks a lot.

[@vedhvijay5602]

Very well explained! Thank you!

[@pachu242424]

Clear information. Great! This things are hard to Find on this kind of topics. Thank you and here is your like and subscribe from Argentina

[@enesb4797]

Hello sir, what is the point of giving different return values?

[@CodeVault]

It's simple. What you return inside main gets passed to the operating system. If it's 0, it's considered a "success", if it's anything else, it's considered an error. So, if I return, let's say, 3 in the main function, I will get in the terminal something like: "Program terminated with exit code 3" And then I could look at my code and find where that 3 is and figure out what happened

[@enesb4797]

@@CodeVault Thank you so much!

[@PetraTToth]

what program do you use to run the code? we programmed c in codeblocks, but that obviously can't run these types of codes and i tried putty, but it's just problematic. also thank you so much for these videos, you're the reason i haven't failed yet in my operation system class.

[@CodeVault]

Glad to be of help. There's this video and the next one in the list presenting how to use VSCode in Linux and how I am using VSCode to run the programs (it's a bit more complex): code-vault.net/course/yx1g2sh6l4:1610029046575/lesson/4wy66ezt7u:1610303902122

[@tongpoo8985]

oh thank god you have a video on this

[@flamendless]

Awesome thanks a lot! Please need some guidance on how to get the output of printf of another program (child) then receive that in the main program (parent) but not after the child is closed or done?

[@CodeVault]

There's this video on the topic: code-vault.net/lesson/43zvcsz6o1:1603732432539

[@beef2244]

Could you show us how to write things to a file. For example if I wanted to have a file with: - The time the program was run - Parent and Child process ID - When processes terminate - Some info about the inode?

[@CodeVault]

There are these videos about working with files: code-vault.net/course/3os73qqz0h:1610029045277 Combine that with what you learned on the processes' playlist and you should be good to go

[@dealvin]

do you have some videos about mmap() function?. Thanks for this video.

[@CodeVault]

No yet

[@yogi3058]

Explanation is good but there is correction here. Else part is parent part of process because fork return number is non zero for Parent process only.

[@CodeVault]

I'm pretty sure that's how it was set up. Do I say in the video otherwise?

[@pablo17349]

Please share your keyboard model, it sounds delicious!

[@CodeVault]

Corsair K65 with red switches I use in that video, although I don't really recommend it. Nowadays I use a Das Keyboard with brown switches. Much easier to type on

[@play_sports_and_read_books]

Should i close the read for parent or write for child if i want to read from more than one child more than one time, or want to read from different children? Or the child wants to send many messages for the parent process, lets say in a loop

[@CodeVault]

If you want to communicate with more children you'll need to open another pipe for each line of communication

[@play_sports_and_read_books]

@@CodeVault i found that out in later videos for you Thank you for this amazing content, it is really helping me in real Time systems course

[@djoykeabyah5904]

Thank you so much for this video! I'm only a bit confused because while following along with the code around 11 min in the video my output showed only 2 printf messages or just one when we removed the break. ➜ ./a.out wrote 8 result is 8 Why is that happening? does that mean that even with the break the parent process is too quick for the child even to give any form of output?

[@CodeVault]

I'm guessing your program just never waits for the child process to finish its execution. Try adding a wait(NULL) before the return of the parent process

[@djoykeabyah5904]

@@CodeVault thanks! I'll try that out!

[@anton78570]

thank you so much! very clear explications!

[@toniiicarbonelll287]

excellent, thank you very much for you work

[@hackraise]

Hello, Thanks for these usefull videos! I was wondering how you can see on VS the definitions of functions that you call, for instance pipe : "Create a one-way communication channel [...] " Thanks for the help :) best

[@CodeVault]

I just installed the C/C++ extension from Microsoft and made sure it pointed to the right folder where the compiler is

[@navidnouri151]

Thank you so much for videos..They are very useful..

[@bhavikdesai6000]

As both the process is running concurrently ,What if Parent process is executed first and read call executed before we actually write something into the pipe?

[@CodeVault]

The read function ALWAYS waits for there to be data in the pipe, similarly the write function ALWAYS waits for there to be space in the pipe's buffer

[@hrishikeshp856]

This video was quite helpful!

[@anupgyawali5122]

Thank You.. all theory explained by simple example :)

[@vanchark]

I came here for 6:54. I was wondering why in my professor's sample code you have to close the other end of the pipe. Turns out it's very simple -- it's because we inherit it but we're not using it haha

[@naseerahmed3162]

Hi , Do you have to wait i the else part at the begenning of paper before reading from the pipe(fd[0]) for the child to write to fd[1] and finish its execution basically i was asking if you can a write call before anything is written to the pipe. please advices

[@CodeVault]

No you don't. read will wait for there to be something in the pipe, similarly write will wait for there to be space in the pipe's buffer.

[@namanchhabra4136]

@CodeVault How can we achieve synchronisation in this ? Please give me some code …

[@CodeVault]

Usually pipe, read and write gives you enough synchronization. You could also used shared semaphores between the processes (I might make a video on this later on)

[@suneelabbigari]

Please upload a playlist on IPC, PIPE, FIFO , MESSAGE QUEUE AND SHARED MEMORY

[@suneelabbigari]

Thank for the reply , Can i expect these concepts ??

[@CodeVault]

There are already videos on pipe and fifo: code-vault.net/course/46qpfr4tkz:1603732431896/lesson/l60w4pa21h:1603732432183 and code-vault.net/course/46qpfr4tkz:1603732431896/lesson/6beteynqqw:1603732432282 respectively. The rest are on my todo list already

[@suneelabbigari]

@@CodeVault Thanks for the reply, please upload videos for message queues , shared memory in depth plss

[@umuttay]

Thanks for the video i really appreciate that. My problem is what should we do when we want to communicate both processes for example: parent process sent "x" and child process read it and child process wants to send "y" so now parent process has to read it.I'm kind a confused here.Isn't pipe for only one way ? I didn't want to bother you on Discord pretty sure you are busy.So glad if you help me

[@CodeVault]

Pipes are generally used for one way communication between processes. That is because if you both read and write to a pipe from a single process, you will most likely read your own content that you just wrote. You have to use 2 pipes in order to communicate both ways. I'll release a video on this next week. (as it's a fairly common issue)

[@umuttay]

@@CodeVault got it thanks again

[@NOPerative]

Excellent video.

[@baranklc6302]

I have a question sir. Why we have to fork right after the pipe? Can't we just pipe first after fork? What is the difference? Apart from sir, everyone who knows the exact answer shall comment under my question too, i really welcome your thoughts. Thank you in advance

[@CodeVault]

pipe() created a pair of file descriptors (basically IDs). If you first fork() and then pipe() you will be left with two different pipes (since pipe() would be called on both processes) and, since the file descriptors would be different you wouldn't be able to communicate between them

[@hackedyou116]

@CodeVault, what if we increase the size of the array? why only size 2?

[@CodeVault]

Only size 2 because a pipe has 2 ends (a read end and a write end). You could increase the size of the array and store multiple pipes if you wanted but you would need to initialize them individually

[@ihoussem3367]

Simple explanation! Thanks again

[@subhashjha2959]

fork return 0, pid, -1, so need to add 3rd condition for fork.

[@enesb4797]

you are the best

[@HedgehogShimmered]

Just a question , shouldn't you put an exit a then end of your child? Because if you make a wait(null) in your father process it might be stuck forever if the child never dies?

[@CodeVault]

I'm actually indirectly calling exit here. There's one more line of code executed after the if block, that is the 'return 0;'. Which is equivalent to 'exit(0);' if done in the main function.

[@hiotasmusic3811]

Hi, what is your VSCode extension which shows you the function's description ? Thank you !

[@CodeVault]

It's the C/C++ extension from Microsoft. Make sure the headers are configured properly otherwise it won't show the tooltips properly

[@hiotasmusic3811]

@@CodeVault ok I see, thank you ! Your videos help me a lot !

[@themodesttraveler745]

i have been watching you videos and there are very good . but im trying to use system(); to call nmap and mysql togther and feed one with inforamtion with the other .do you have any videos on piping console output and input

[@CodeVault]

Yes, there's this video: code-vault.net/lesson/43zvcsz6o1:1603732432539

[@timog7358]

fantastic video

[@kiseijuu7420]

I have multiple question. Why u dont wait at the end of the parent? Since u dont wait, why did the child process always run before the parent? For exemple why u didnt get an error telling u that value y isnt initialised cause we learned that u never know which process execute first if u dont wait. Second, how did u open the fd? Dont u need to use open() after using a pipe? Cause pipe juste gives u fd, but they dont actually open them right? + dont u need to give them the permission to either read or write in them? And last question, since u use a protection for ur fork, ur write and ur read, why didnt u close the fd before returning each error value? Cause what i see here is that if u fail to write, then u return 2 if i remember correctly, and only fd[0] is closed, while fd[1] remains open no? Except from these questions, i find ur videos really helpful thanks 🙏 , cause i noticed that since the beginning i only ask questions without thanking u lol 😂, sry about that.

[@CodeVault]

1) read() always waits for there to be something written to the pipe 2) pipe() already opens the fds so no open() call is needed 3) You're correct. The better solution would be to close the fds before returning. But, since we are returning, the OS will automatically close the fds for us. It's just good practice to close them but not required. It's also a good idea to close them once you don't need them anymore if it's a long-running process

[@ishikasharma4045]

I have a question. How do we pass an array of values using for loop from parent to child or vice versa?

[@CodeVault]

There's actually a video on this: code-vault.net/lesson/phac6gv4cy:1603733529763