Virtually all contemporary operating systems-including Wiridows XP, Linux, Mac OS X, Solaris, andTru64 UNIX (formerly Digital UNIX)-support kernel threads Many-to-one model The many to one model maps many user-level threads to one kernel thread. Mac OS X is incredibly slow, between 2 and 5(!) times slower, in creating new threads, as it doesn't use kernel threads, and has to go through extra layers (wrappers). Linux Threads Frequently Asked Questions (FAQ) by Sean Walton, KB7rfa [email protected] (Last revised 19 Sep 1996) See also. May speed your access. Caution This FAQ is more than a two years out-of-date. POSIX-threads are now a standard part of all modern Linux distributions. The new glibc version 2 (linux libc version 6.0) is fully re-entrant and supports threads in a fully compliant manner. The default Linux thread implementation is with kernel-space threads, not user-space threads; these threads will schedule properly on an SMP architecture. You may still find this FAQ useful if you are looking for user-space threads, DCE threads, a non-standard threads API, or for threads tools for a language other than C/C++/perl/tcl/scheme, or if you are upgrading an older system. The 'LinuxThreads' package (below) has become the default package for Linux distributions, so you will probably want that if upgrading. The MIT (Provenzano) threads package is popular among some folks. Since Sean Walton has moved on to bigger & better things, there is currently no maintainer for the FAQ. If anyone wants to bring this FAQ up-to-date, or can offer an otherwise improved and updated FAQ, please contact me, Linas Vepstas, and I will post your updates and/or redirect this page to your page. Introduction This FAQ is designed to answer several frequently asked questions about Linux threads. For an in-depth view of threads or Linux threads join the discussions on. Since I am only conveying the information (and not an expert), please direct your specific questions to c.o.l.d.s or comp.programming.threads. If you have suggestions/additions/revisions to this document, please email. Limitations This is not a discussion on the various implementations of threads: it is specifically for Linux threading. If you want to see a comparison between systems or would like to promote some other system than is intended here, write your own FAQ. Nevertheless, I welcome comments pertinent to the topic and will gladly add your input. Sound drivers for vmware mac os x download. Credits A special thanks to those who significantly helped me put this together: (for a lot of theory) and (for his list of sources). INDEX • • • • • • • • • • • • • • • • What are threads (user/kernel)? Threads are 'light weight processes' (LWPs). The idea is a process has five fundamental parts: code ('text'), data (VM), stack, file I/O, and signal tables. 'Heavy-weight processes' (HWPs) have a significant amount of overhead when switching: all the tables have to be flushed from the processor for each task switch. Also, the only way to achieve shared information between HWPs is through pipes and 'shared memory'. If a HWP spawns a child HWP using fork(), the only part that is shared is the text. Threads reduce overhead by sharing fundamental parts. By sharing these parts, switching happens much more frequently and efficiently. Also, sharing information is not so 'difficult' anymore: everything can be shared. There are two types of threads:. User-Level Threads User-level avoids the kernel and manages the tables itself. Often this is called 'cooperative multitasking' where the task defines a set of routines that get 'switched to' by manipulating the stack pointer. Typically each thread 'gives-up' the CPU by calling an explicit switch, sending a signal or doing an operation that involves the switcher. Also, a timer signal can force switches. User threads typically can switch faster than kernel threads [however, Linux kernel threads' switching is actually pretty close in performance]. User-level threads have a problem that a single thread can monopolize the timeslice thus starving the other threads within the task. Also, it has no way of taking advantage of SMPs (Symmetric MultiProcessor systems, e.g. Lastly, when a thread becomes I/O blocked, all other threads within the task lose the timeslice as well. Solutions/work arounds.
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