Is anyone aware of what operations are involved when a call to pthread_self() is made, obtaining the unique thread ID on a Ubuntu system (or even any Linux flavour)?
Specifically, to retrieve the thread id, is there any locking required or atomic operations?
I'm building an application for multi-core systems (in C using pthreads) which needs to be scalable and I'm planning to call this function quite often, hence I need some idea how "expensive" it is to do so.
The internals of this function are some pretty hairy inline assembly, differing wildly from architecture to architecture. I can't tell precisely what it's doing. But from the comments, it sure looks like they're trying hard to make it minimal(down to the instruction-level, even) and nonblocking.
Last edited by Corona688; 06-03-2010 at 07:46 PM..
Which I believe is accessing the Thread Control Block of the running thread which resides here in the gs register, specifically the offset containing the tcb address, I think.
This should result in a pretty quick, "inexpensive" and scalable operation then. Wondered if there was a chance that another thread could overwrite the register where this value is written before the calling thread retrieved it, (the volatile keyword isn't used) but I suppose this function would be useless if that was a possibility. This function must be thread safe, right?
Of course it's thread-safe, not much point having it otherwise. It may be using registers that it wouldn't have write-access to, as well; unlike the old linuxthreads, NPTL operates with pretty low-level support by the kernel. (not that NPTL runs as root -- more that things more fundamental than system calls exist in the kernel for it. On MIPS for example, it monopolizes one of only four special hardware registers a MIPS chip has.)
I can't think of a good reason to call pthread_self a lot.
why?
I doubt it's atomic, why should it need to be, it's unique to the thread.
it's only used for detaching or scheduling.
i would start detached if need be. scheduling I haven't tried.
"keep it simple".
"I can't think of a good reason to call pthread_self a lot.
why?"
It's a long story, but basically I need a way of accessing application specific "context" information I have stored which is different depending on which thread is running. Using pthread_self() provides a way of having a unique key to that information regardless of where within a program, the execution is. Because pthread_self doesn't require any arguments, I don't need to carry around a parameter everywhere with that key, hence the application doesn't even have to be aware of the mechanism.
I need to re-install ubuntu on a system with ubuntu 14.04 already installed. I have the cd but can not seem to boot from it or find the installer. Is there a way to re-install from the command line or how do I do a fresh re-install? Thank you :)
---------- Post updated at 10:13 AM... (2 Replies)
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Gurus,
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