PTHREAD_DETACH(3P)

💅 PTHREAD_DETACH(3P) — POSIX Programmer's Manual 💅

okay bestie, welcome to the POSIX Programmer's Manual ✨ this one's about pthread_detach, and it's genuinely a glow-up for your thread hygiene, no cap.

⚠️ PROLOG — real talk first: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so go check the corresponding Linux manual page for the deets on Linux behavior), or the interface might not even be implemented on Linux at all. iykyk 🙈

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🌸 NAME 🌸

pthread_detach — detach a thread 💫

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✨ SYNOPSIS ✨

#include <pthread.h>

int pthread_detach(pthread_t thread);

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🦋 DESCRIPTION 🦋

so the way pthread_detach() works is: it shall indicate to the implementation that storage for the thread thread can be reclaimed once that thread terminates. that's it, that's the whole vibe. ✨

and listen — if thread has not terminated yet, pthread_detach() shall not cause it to terminate. it's not a murder function, it's a cleanup function, periodt. 💅

💀 the behavior is undefined if the value specified by the thread argument to pthread_detach() does not refer to a joinable thread. undefined behavior, bestie. we do not do that.

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🎀 RETURN VALUE 🎀

if the call succeeds, pthread_detach() shall return 0. otherwise, an error number shall be returned to indicate the error. simple as that 🫶

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🔥 ERRORS 🔥

the pthread_detach() function shall not return an error code of [EINTR]. nope, not a thing, don't ask.

the following sections are informative. 👑

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🌈 EXAMPLES 🌈

None. — literally none, we're keeping it mysterious 🧚

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💜 APPLICATION USAGE 💜

None. — also none. the manpage said "figure it out" and honestly? respect. 😌

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👑 RATIONALE 👑

okay this is the part where the standard explains itself, and it ate:

the pthread_join() or pthread_detach() functions should eventually be called for every thread that is created, so that storage associated with the thread may be reclaimed. yes, every single one. no orphaned thread storage in this house 🏠✨

so, it has been suggested that a "detach" function is not necessary — that the detachstate thread creation attribute is sufficient, since a thread need never be dynamically detached. however, need arises in at least two cases:

1. In a cancellation handler for a pthread_join() it is nearly essential to have a pthread_detach() function in order to detach the thread on which pthread_join() was waiting. Without it, it would be necessary to have the handler do another pthread_join() to attempt to detach the thread — which would both delay the cancellation processing for an unbounded period and introduce a new call to pthread_join(), which might itself need a cancellation handler. A dynamic detach is nearly essential in this case. 💀 (this is the "not me nesting joins in a cancellation handler" scenario)
2. In order to detach the "initial thread" (as may be desirable in processes that set up server threads). 👑

and some implementation notes, straight from the source, no edits:

• If an implementation detects that the value specified by the thread argument to pthread_detach() does not refer to a joinable thread, it is recommended that the function should fail and report an [EINVAL] error.
• If an implementation detects use of a thread ID after the end of its lifetime, it is recommended that the function should fail and report an [ESRCH] error.

⚠️ note the words "recommended" and "detects" — these are recommendations for implementations, not promises to you. don't build your whole app on them 💅

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🌟 FUTURE DIRECTIONS 🌟

None. — the future is bright but this section is empty, and that's iconic. ✨

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🫶 SEE ALSO 🫶

• pthread_join()
• The Base Definitions volume of POSIX.1‐2017, <pthread.h>

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💖 COPYRIGHT 💖

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie 🎀 brought to you by IEEE/The Open Group, dated 2017, filed under PTHREAD_DETACH(3P) — go detach something responsibly, mwah 💋