Talk:Thread (computing)

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Untitled

Thanks for fleshing out the stub, Lee. I knew this stuff, but it wasn't on the tip of my tongue (one step further buried in the memory banks). User:Ed Poor

Renaming

Just for note. I renamed the article to thread (computer science) because threading not necessarily only in software enginnering. -- Taku 16:14, Mar 28, 2004 (UTC)

System call for a context switch?

The article says "Typically fibers are implemented entirely in userspace. As a result, context switching between fibers in a process is extremely efficient: because the kernel is oblivious to the existence of fibers, a context switch does not require a system call." Why would a context switch require a system call in any situation? Is it talking about non-preemptive multitasking? If so, wouldn't it be better if the article mentioned it? If the article isn't intended to say that a system call is required for a context switch, then it would be better if it were cleared up in the article. It's misleading. It would help if the article (that section) is clearer anyway.

Yeah, it would be more clear to say "a context switch does not require a kernel entry" or some such. I'm not sure that it matters whether or not the thread implementation is preemptively scheduled or not: in a cooperatively scheduled implementation of kernel threads, there is still some kernel state associated with the currently-running thread, and so a kernel entry is some kind is required to switch that state, right? The point is somewhat academic, anyway, as cooperatively-scheduled kernel thread implementations are rare AFAIK. Neilc 04:23, 20 Jun 2005 (UTC)

I made that change. I was trying to figure out how to get something about pre-emptive scheduling of threads involving the kernel programming a hardware interrupt in order to stop the current thread, but couldn't figure out how to word that decently. :) Dianne Hackborn 05:51, 22 Jun 2005 (UTC)

Books

I've added Three .NET threading resources - two of these are admittedly my own published works. I've added them only because there were no other .NET programming resources listed. Feel free to remove them if you feel they are inappropriate. Both of these books are out of print but you can still find them quite often at book stores and from secondary book stores. I have a fourth book published that is still on the market that I didn't list because it covers two other areas as well as threading. The title is Pro .Net 1. 1 Remoting, Reflection, and Threading and the ISBN is 1-590-59452-5. While it is more "current", the fact that it covers two other topics doesn't seem to make it appropriate for this article. Once again, feel free to add it if you feel otherwise. - Sleepnomore 15:46, August 26, 2005 (UTC)

The process with threads image

The potentially leads to misinterpretations.

As it is, unwary readers may think processes are always made up of threads, which is not true. Actually, in many contexts, threads break processes into tasks.

I propose the image, as it is now, to be removed. M. B., Jr. (talk) 23:58, 18 December 2022 (UTC)

And in the context of the Mach kernel, a task has multiple threads - and a task corresponds somewhat to a process; Darwin's XNU kernel constructs each UN*X process atop a Mach task (and Darwin's pthread library constructs pthreads atop Mach threads).

So what are your defintions of process, thread, and task here? Guy Harris (talk) 01:05, 19 December 2022 (UTC)

Hi, Guy Harris. I'm glad we agree, since I did not state the opposite whatsoever. As for definitions, I'm not sure what you mean by "your". This is an article about the concept, not about particular implementations. In Modern Operating Systems, Tanenbaum writes that "several different models are possible". Notwithstanding, implementations may be provided in a proper context-wise manner, e.g., precisely explaining the case in the image's subtitle. This way, readers are able to understand the Mach way is not a general rule. Regards, M. B., Jr. (talk) 20:14, 19 December 2022 (UTC)

You said "many contexts, threads break processes into tasks". I noted that, in Mach, one task, in Mach terminology, can have multiple threads, in Mach terminology, so, in that context, a thread doesn't "break processes into tasks" - there is, at least in Darwin (and probably other systems with Mach-based kernels), there's a one-to-one correspondence between Mach tasks and processes.

And what I mean by "your defintions of process, thread, and task here" is "If you mean by "process" that which is described in process (computing), and if you mean by "thread" that which is described in thread (computing), what do you mean by "task" when you say that "threads break processes into tasks"? And if that isn't what you mean by "process" or "thread", what do you mean?"

Where, and in which edition, does Tanenbaum write that "several different models are possible"? I need to know precesly what he was referring to. He could be referring to the different types of threads mentioned in thread (computing) § Processes, kernel threads, user threads, and fibers, or to the threading models mentioned in thread (computing) § Threading models, or to something else?

And the image is pretty straightforward - a process has multiple threads of control, so that the process can be doing multiple things in parallel. By your use of the word "task", are you referring to the "things" being performed by the threads?

I only brought up Mach because it uses the term "task" as a technical term; OS/360 and its successors use "task" in a different sense, where it seems to cover both what we might think of as processes and what we might think of as threads. The point is that "task" doesn't seem to have a commonly-used technical definition in the fashion that "process" and "thread" appear to; if you wan tto be clearly understood here, a good first step might be to indicate what you mean by "task", so we can determine how "processes are made up of threads" and "threads break processes into tasks" mean something different? Guy Harris (talk) 22:55, 19 December 2022 (UTC)

Hi, Guy Harris. Thanks for your feedback. Discussions like this one make Wikipedia awesome. Indeed, the concept of task is context-subordinated. I'm referring to the OS concept, not the application one. And yes, the process to task conversion constitutes a thread hijack technique (and maybe a thread rescue technique as well?). Because processes themselves live in the main memory. Despite the name, the CPU deals with threads and tasks, not processes. If one wants processes' data to be actually processed, such data should be somehow turned into threads and/or tasks. Anyway, the point is: it is probably in the best interest of Wikipedia's readers to understand concepts, and not stick to particular definitions and/or implementations. The book is ISBN 0-13-595752-4, chapter 12 Processes and Processors in Distributed Systems. Regards, M. B., Jr. (talk) 17:11, 20 December 2022 (UTC)

So where is the OS concept of a "task", as distinct from a "thread" or a "process", defined?

And what is a "process to task conversion", and how does it "constitute a thread hijack technique (and maybe a thread rescue technique as well?)"

Processes "live in the main memory" in a number of senses: 1) in many operating systems, one resource that a process has and that is shared by all the threads in the process is its address space - not all of which necessiarly resides in main memory - and 2) the OS maintains state about the process, typically in wired main memory. Point 2), however, applies to threads and, in the case of OSes that use the term "task", tasks.

And most CPUs deal with instructions, not threads (in the thread (computing) sense) or tasks. The notion that a CPU is working on a particular "thread", "process", or "task" is, on most CPUs and operating systems, defined by the operating system, not by the CPU. Guy Harris (talk) 20:50, 20 December 2022 (UTC)