Re: processes, tasks, threads
Re: processes, tasks, threads
- Subject: Re: processes, tasks, threads
- From: Jens Alfke <email@hidden>
- Date: Sat, 10 Apr 2010 09:09:27 -0700
A thread is just a flow of control -- a CPU state (registers) and a stack.
A process is what you think of as a program, what's listed in 'top' or Activity Monitor. It's a set of threads running in a memory address space plus a set of privileges (user and group ID, resource quotas, etc.)
"Task" is I think a synonym for process. I haven't heard "flow" before, but I'd guess it means the same as thread.
The above definitions hold for pretty much every OS, including Linux.
The notion of thread can get tricky because there can be multiple types of threads. The OS kernel manages threads and has system calls for them. There are portability APIs like pthreads that wrap these. But it's also possible for user code to implement it's own threading system, using calls like setjmp and ucontext that let you save and restore CPU state. These are often called "green" threads, a name that came from the original Java runtime. The advantage of these is that they can be extremely lightweight because they don't consume any kernel resources. But they're more difficult to work with because the kernel and system libraries don't understand them. (You usually see green threads in interpreted language runtimes like Java and Ruby.)
--Jens {via iPad}
On Apr 10, 2010, at 6:06 AM, Ariel Feinerman <email@hidden> wrote:
> Hi,
> sorry for stupid question. What is the difference between process, task, flow and thread in the Darwin? What kind of relationsheeps between calls fork(), exec() and pthreads or mach threads? I heard that in some OS process and thread are the same entity at least in Linux.
> Thank you in advance,
>
> --
> best regards
> Ariel
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