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[[!meta copyright="Copyright © 2002, 2003, 2010 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
License|/fdl]]."]]"""]]
A Mach *thread* belongs to exactly one [[task]], and is the means of execution.
The task supplies the resources.
Mach threads are implemented inside the [[kernel]], like in many operating
systems, unlike some user-level thread packages (aka "green" threads).
A thread (theoretically) runs concurrently with all the other threads of a
system. If the system provides several processors, they can be used for
simultaneously running either several threads of the same task, or several
threads of different tasks. <!-- This is called SMP; the processors use
*shared memory*. --> [[!tag open_issue_documentation]] <!-- This needs a new
page, also covering Mach's `processor_set`s, and non-SMP, but still
multiprocessor systems. --> (But this is currently not support in [[GNU
Mach|gnumach]].)
It is easy for the kernel to switch execution from one thread to another one
inside the same task: essentially, it only involves exchanging a few processor
registers' state.
Threads have scheduling parameters and maintain various statistics about
themselves.
On GNU/Hurd, APIs for Mach threads and thereabouts are provided by the
[[hurd/libthreads]] (cthreads), and [[libpthread]] (POSIX Threads) packages.
A task backing a thread is the basis for a [[UNIX process|unix/process]].
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