Beej’s Guide to Unix Interprocess Communication. Version (May) [ ]. Intro. You know what’s easy? fork() is easy. You can. Beejs Guide to Unix IPCBrian “Beej Jorgensen” [email protected] This guide is written in XML using the vim editor on a Slackware. I owe my career to Beej. I was getting burnt out of web development and his guides (along with Jesse Storimer’s books) made programming fun.

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Also check out his guide to C programming [0] and fod guide to network programming [1] [0] http: I owe my career to Beej. I was getting burnt out of web development and his guides along with Jesse Storimer’s books made programming fun for me again. I highly recommend learning how Unix systems work. It’s a lot of fun and opens up a whole new world of programming! I’m feeling the same way about web, I’d like to transition to something similar.

I quite enjoy programming in C, so hopefully that helps. What are you doing at your job now? How did you go about making the switch from web to systems? Has it paid off with an increase in enjoyment? Iipc be told, a significant portion of my day job is still web application stuff. Only the lucky few get to hack on databases, hypervisors and file systems for a living!

But, armed with the knowledge of sockets, processes, etc. But even before I was able to work the knowledge into my day job, nothing beats the dopamine rush of learning things that fascinate you! The rabbit holes that learning the basics of Unix have opened feel like they could occupy my hobbyist hours for the rest of my life.

Beej’s Guide to Unix IPC () | Hacker News

Its amazing how we think the grass is greener. I have been doing systems programming for the past 7 years and have been thinking about moving over to JS based web development for the past few months. Actually both of you are right. You need a break from what you have been doing from a long time. Perhaps exchanging your jobs with one another might help. I think we humans just need change every now and then. Even when the problems and tools we use to solve those problems never change, we still somehow get upset with the tools ofr the problems.

Thank you for your efforts, Brian! Something I’ve struggled to implement on Linux is cross-process multicast notifications, where any process foe post and multiple subscribed processes receive it.

Beej’s Guide to Unix Interprocess Communication | Hacker News

On OS X there’s notify 3 which is very nice. Any good options on Linux, other than writing my own socket server? The solution for this kind of problem will depend heavily on what type of messages you’re trying to send.

When messaging becomes that complex, there ofr often other things that impact the overall design in important ways that need need to be considered. For example, if I was implementing something that is usually associated with user events rare-ish, basically zero bandwidth, complex signal with stateful messaging semanticsI would probably just write a simple server to manage it all.


This has an advantage of centralizing any messaging complexity and lets you manage any multi-message state easily.

Rebroadcasting messages to allow peer-to-peer messaging would be a trivial addition. For something that requires very fpr latency e.

Here, the need for low latency dictated the design. Of course, this means managing locks. Not fun, but a cost that is sometimes worth paying. There really isn’t a one-size-fits all solution. Or, as troglobit said, TIPC. I keep forgetting that we now have it has an option. Thanks for the reply. My use case is very simple: Coalescing or even occasional drops are fine. I did originally use a Unix domain socket server, but that added a lot of complexity: My new solution on Linux is a total hack: Clients see that the FIFO became readable, and that change represents the notification.

The sender then drains the data it wrote, so that the FIFO becomes unreadable again. This is a total abuse of FIFOs, but it’s proven to be much simpler than trying to manage a separate server.

I’ve never heard of TIPC. From a little searching it looks like it’s very capable but geared towards clusters, and is overkill for my use case. What do you think? I tried that once, and it was unreliable. Only some clients woke up.

A colleague wrote up a blog post about the various alternatives that were evaluated before settling on that approach: Ha ha ha, that’s great! If we are sent to programmer purgatory, at least we’ll have each other. If drops are fine, TIPC is probably overkill. I would probably just wrap something generic using UNIX domain sockets up into a library guiee re-use that as needed. Depending on your permissions requirements[1], and if you really only need a signaling flag, have you considered the filesystem?

Just touch a file in a well-defined directory named after the event that happened, and poll it periodically.

Beej’s Guide to Unix IPC

Removing the file clears the flag. Signals can coalesce, but you should never drop any. You can poll a directory that will normally be empty without much CPU load the directory inode will be cached most of the time. You could setup a multiple listeners by giving them their own “inbox” directory, like.

Your signals also persist across programs shutdowns and crashes – you can send and receive even when the other side isn’t running – and your state can persist across reboots. Also, you can leverage some of the guarantees provided by the kenel’s vfs layer. For example, rename 2 is atomic, so you can send small data payloads by writing to a different name first.

Those events can be received either in a simple blocking style by letting poll 2 wake-up your process. The man oage inotify 7 should have an example. Making a group specific to the message sending can help. Thank you for this thoughtful reply. There’s a variety of options if I’m willing to poll, including shared memory or the filesystem idea you outline, but I hope to avoid polling for hygienic reasons.


I also explored inotify but found it to be unreliable https: That’s why I like inotify in blocking mode – the call to poll is just to wake up the process I think you could just blocking-read the inotify file handle? I haven’t tried it directly.

The point of using inotify is that you don’t need to poll, because the kernel send your process reliable events instead over a file handle. The use of poll 2 is just a consequence of the interface using a file handle.

As, I originally said, though, there is certainly no one-size-fits-all solution, these are just a few of the available options, which may not be apropriate for your situation. I like blocking inotify in principle – the problem is that it just didn’t work! I think there is a gap in the Linux APIs in this area. Its multicast IPC mechanisms are just too heavyweight. You can do it with shared memory. One writer writes and multiple readers can observe. I did this for both low latency and throughput reasons.

In general you have to be very careful how you handle it and consider various consistency and failures scenarios. The main part of memory layout looks something like this: You’d probably have to declare this using the ‘volatile’ keyword.

Otherwise compilers will optimize away access to part of this seemingly unused variables. Then it works like this: Data gets written to buffer. Also, note these counters also function as total counts of items written and so each reader cand determine how far ahead the writer is. Compiler could separate the update as multiple instructions and say, increment the lower part of the value, then the upper part. Writer could get pre-empted between those two instructions, so you could get this strange torn value.

But, you might be reading data you didn’t expect. Whether that works for your use case or not you’ll have to see. Don’t also forget about the slow and stupid multicast mechanism — writing to a file. Some file operations can be atomics renaming a file. And some operating systems let you watch the files for changes. Classic signals are tricky You can actually implement a basic pubsub both one-to-many and many-to-many mechanism using FIFOs and file system permissions in a particular fashion known as a fifodir: Specifically, dbus signals without a destination are routed to all connections with match rules added with org.