PTHREAD_SPIN_DESTROY(3P)

💖 PTHREAD_SPIN_DESTROY(3P) — POSIX Programmer's Manual 💖

okay bestie, welcome to the POSIX Programmer's Manual, page PTHREAD_SPIN_DESTROY(3P). we're doing spin locks today and honestly? they're giving "tiny, fast, feral". let's get into it 🎀

✨ PROLOG ✨

so this manual page is part of the POSIX Programmer's Manual. but heads up: the Linux implementation of this interface may differ — so pls consult the corresponding Linux manual page for the deets on Linux behavior — or, plot twist, the interface might not even be implemented on Linux at all. 🙈

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🌸 NAME 🌸

pthread_spin_destroy, pthread_spin_init — destroy or initialize a spin lock object. that's it, that's the job. two functions, one little lock, main character energy.

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🦋 SYNOPSIS 🦋

#include <pthread.h>

int pthread_spin_destroy(pthread_spinlock_t *lock);
int pthread_spin_init(pthread_spinlock_t *lock, int pshared);

look at those signatures, so clean, so crisp. ✨

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💅 DESCRIPTION 💅

okay so first up: pthread_spin_destroy() shall destroy the spin lock referenced by lock and release any resources used by the lock. 💀 but here's the thing — the effect of using that lock afterwards is undefined until the lock gets reinitialized by another call to pthread_spin_init(). and the results are undefined if you call pthread_spin_destroy() while a thread is still holding the lock, or if you call it with an uninitialized thread spin lock. like, don't do that. seriously. no cap.

then we have pthread_spin_init(), which shall allocate any resources required to use the spin lock referenced by lock and initialize the lock to an unlocked state. fresh lock, clean slate, slay. 🫶

now, if the Thread Process-Shared Synchronization option is supported and the value of pshared is PTHREAD_PROCESS_SHARED, the implementation shall permit the spin lock to be operated upon by any thread that has access to the memory where the spin lock is allocated — even if it's allocated in memory that is shared by multiple processes. cross-process besties, we love to see it. 🌈

also, see Section 2.9.9, Synchronization Object Copies and Alternative Mappings for further requirements. iykyk.

more undefined behavior warnings, bc of course:

• the results are undefined if pthread_spin_init() is called specifying an already initialized spin lock.
• the results are undefined if a spin lock is used without first being initialized.

and if pthread_spin_init() fails? the lock is not initialized and the contents of lock are undefined. 😭

only the object referenced by lock may be used for performing synchronization. just that one. not its cousins, not its photocopies.

and the result of referring to copies of that object in calls to pthread_spin_destroy(), pthread_spin_lock(), pthread_spin_trylock(), or pthread_spin_unlock() is undefined. so like... don't make copies. periodt. 💅

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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. that's the whole vibe check. 💖

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🔥 ERRORS 🔥

the pthread_spin_init() function shall fail if:

• EAGAIN — the system lacks the necessary resources to initialize another spin lock. (girl, we're out of lock juice. 😭)
• ENOMEM — insufficient memory exists to initialize the lock. (no room, no lock, no service. 💀)

also, these functions shall not return an error code of [EINTR]. noted. ✨

the following sections are informative. (translation: the tea below is educational, not mandatory 🍓)

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🎀 EXAMPLES 🎀

None. — nothing here bestie, move along. 🙈

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💜 APPLICATION USAGE 💜

None. — also empty. the void is giving minimalist. ✨

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👑 RATIONALE 👑

okay so the reasoning, and it's all about "recommended" behavior here:

• if an implementation detects that the value specified by the lock argument to pthread_spin_destroy() does not refer to an initialized spin lock object, it is recommended that the function should fail and report an [EINVAL] error.
• if an implementation detects that the value specified by the lock argument to pthread_spin_destroy() or pthread_spin_init() refers to a locked spin lock object — or detects that the value specified by the lock argument to pthread_spin_init() refers to an already initialized spin lock object — it is recommended that the function should fail and report an [EBUSY] error.

so like, implementations should catch your mess, but "recommended" means it's not a promise. stay safe out there. 🫶

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🧚 FUTURE DIRECTIONS 🧚

None. — the future is... nothing. iconic. 💅

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🌈 SEE ALSO 🌈

• pthread_spin_lock()
• pthread_spin_unlock()

and from 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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that's the whole page, bestie!! this one came to you from IEEE/The Open Group, dated 2017, and it signs off as PTHREAD_SPIN_DESTROY(3P) — go forth, initialize your locks, destroy them responsibly, and never touch a copy. mwah. 💅✨🫶