PTHREAD..._DESTROY(3POSIX)

💅 PTHREAD..._DESTROY 💅

okay bestie, we're in the POSIX Programmer's Manual rn, and today's topic is barriers — the pthread kind, not the emotional kind (though honestly, same energy). 🎀

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🌈 PROLOG

So here's the tea: this manual page is part of the POSIX Programmer's Manual. That means the Linux implementation of this interface may differ — like, if you're on Linux, go check the corresponding Linux manual page for the actual deets on Linux behavior. Or, plot twist, the interface might not even be implemented on Linux at all. 🙈 So vibe check your platform first, bestie.

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✨ NAME ✨

pthread_barrier_destroy, pthread_barrier_init — destroy and initialize a barrier object. Two functions, one mission: barrier management. 💖

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🦋 SYNOPSIS 🦋

#include <pthread.h>

int pthread_barrier_destroy(pthread_barrier_t *barrier);
int pthread_barrier_init(pthread_barrier_t *restrict barrier,
    const pthread_barrierattr_t *restrict attr, unsigned count);

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🌸 DESCRIPTION 🌸

💀 pthread_barrier_destroy()

This one shall destroy the barrier referenced by barrier and release any resources used by the barrier. That's it, that's the job.

But listen — the effect of using the barrier afterwards is undefined until it gets reinitialized by another call to pthread_barrier_init(). And an implementation may use this function to set barrier to an invalid value, so don't go poking at it like it's still valid. 💀

🚨 Results are undefined if pthread_barrier_destroy() is called when any thread is blocked on the barrier, or if this function is called with an uninitialized barrier. Like, do not do that. That's not a vibe, that's a crash.

✨ pthread_barrier_init()

This one shall allocate any resources required to use the barrier referenced by barrier, and shall initialize the barrier with attributes referenced by attr.

If attr is NULL, the default barrier attributes shall be used — the effect is the same as passing the address of a default barrier attributes object. So NULL is lowkey just the "I trust the defaults" move. 🫶

🚨 Results are undefined if: - pthread_barrier_init() is called when any thread is blocked on the barrier (that is, has not returned from the pthread_barrier_wait() call) - a barrier is used without first being initialized - pthread_barrier_init() is called specifying an already initialized barrier

All three? Undefined. No cap. 😭

🔢 the count argument

The count argument specifies the number of threads that must call pthread_barrier_wait() before any of them successfully return from the call. And the value specified by count must be greater than zero. Zero is not it, bestie. 🚫

If the pthread_barrier_init() function fails, the barrier shall not be initialized, and the contents of barrier are undefined. So a failed init leaves you with... mystery. 🎁

Also, see Section 2.9.9, Synchronization Object Copies and Alternative Mappings for further requirements — yes, there's homework. 📚

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🎀 RETURN VALUE 🎀

Upon successful completion, these functions shall return zero. Otherwise, an error number shall be returned to indicate the error. So: 0 = slay, anything else = read the next section. 💅

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🔥 ERRORS 🔥

The pthread_barrier_init() function shall fail if:

• EAGAIN — the system lacks the necessary resources to initialize another barrier. The system said "no more, I'm full." 😭
• EINVAL — the value specified by count is equal to zero. Told you, zero is not it.
• ENOMEM — insufficient memory exists to initialize the barrier. Out of memory, out of luck.

⚠️ These functions shall not return an error code of [EINTR]. So don't sit around waiting for that one. It's not coming. 👑

The following sections are informative. (aka: the lore, not the law 📖)

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🌈 EXAMPLES 🌈

None. Literally nothing here. We move. 💀

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🦋 APPLICATION USAGE 🦋

None. Also empty. The void is giving minimalist. ✨

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💜 RATIONALE 💜

This is the "why tho" section, and it's all about what an implementation should do if it detects nonsense:

• If an implementation detects that the value specified by the barrier argument to pthread_barrier_destroy() does not refer to an initialized barrier object, it is recommended that the function should fail and report an [EINVAL] error. 🚩
• If an implementation detects that the value specified by the attr argument to pthread_barrier_init() does not refer to an initialized barrier attributes object, it is recommended that the function should fail and report an [EINVAL] error. 🚩
• If an implementation detects that the value specified by the barrier argument to pthread_barrier_destroy() or pthread_barrier_init() refers to a barrier that is in use (for example, in a pthread_barrier_wait() call) by another thread, or detects that the value specified by the barrier argument to pthread_barrier_init() refers to an already initialized barrier object, it is recommended that the function should fail and report an [EBUSY] error. 🚩🚩🚩

So basically: uninitialized stuff → [EINVAL], busy/in-use/already-initialized stuff → [EBUSY]. Recommended, not required. iykyk. 💅

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🧚 FUTURE DIRECTIONS 🧚

None. The future is... nothing. Iconic of it honestly. ✨

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🌟 SEE ALSO 🌟

• pthread_barrier_wait() — go read that one too, it's the whole point of the barrier fr fr
• The Base Definitions volume of POSIX.1‐2017, <pthread.h> — the header where it all lives

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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. So if they disagree, the Standard wins. Periodt.

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 💖 this one came from the IEEE/The Open Group, 2017 — POSIX era, vintage, iconic, no notes. go forth and initialize your barriers responsibly. 🌸💅✨