PTHREAD...PROTOCOL(3POSIX)

PTHREAD...PROTOCOL 💅✨

okay bestie, welcome to the POSIX Programmer's Manual, section 3POSIX — and no, I did not make that name up, that's literally what the page is called, dots and all. sit down, grab a strawberry 🍓, we're talking mutex protocols.

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📢 PROLOG

This manual page is part of the POSIX Programmer's Manual. Heads up though: the Linux implementation of this interface may differ (so go consult the corresponding Linux manual page for the details on Linux behavior), or the interface might not even be implemented on Linux at all. 💀 yeah. rude, but true.

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🌸 NAME

pthread_mutexattr_getprotocol, pthread_mutexattr_setprotocol — get and set the protocol attribute of the mutex attributes object (REALTIME THREADS). yes it's giving realtime, yes it's giving threads, yes we're obsessed. 🫶

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✨ SYNOPSIS

#include <pthread.h>

int pthread_mutexattr_getprotocol(const pthread_mutexattr_t
    *restrict attr, int *restrict protocol);
int pthread_mutexattr_setprotocol(pthread_mutexattr_t *attr,
    int protocol);

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💖 DESCRIPTION

So. pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() respectively get and set the protocol attribute of a mutex attributes object pointed to by attr, and that object needs to have been previously created by pthread_mutexattr_init(). no creating it in the group chat on the fly, bestie.

The protocol attribute defines the protocol to be followed in utilizing mutexes. The value of protocol may be one of:

• PTHREAD_PRIO_INHERIT
• PTHREAD_PRIO_NONE
• PTHREAD_PRIO_PROTECT

all three of which are defined in the <pthread.h> header. The default value of the attribute shall be PTHREAD_PRIO_NONE. (default = chill, no drama, no priority games. ✨)

When a thread owns a mutex with the PTHREAD_PRIO_NONE protocol attribute, its priority and scheduling shall not be affected by its mutex ownership. it's giving unbothered. 💅

When a thread is blocking higher priority threads because of owning one or more robust mutexes with the PTHREAD_PRIO_INHERIT protocol attribute, it shall execute at the higher of its priority or the priority of the highest priority thread waiting on any of the robust mutexes owned by this thread and initialized with this protocol. (so it levels up. the way that it levels up. 👑)

When a thread is blocking higher priority threads because of owning one or more non-robust mutexes with the PTHREAD_PRIO_INHERIT protocol attribute, it shall execute at the higher of its priority or the priority of the highest priority thread waiting on any of the non-robust mutexes owned by this thread and initialized with this protocol. same energy, non-robust edition. 🌈

When a thread owns one or more robust mutexes initialized with the PTHREAD_PRIO_PROTECT protocol, it shall execute at the higher of its priority or the highest of the priority ceilings of all the robust mutexes owned by this thread and initialized with this attribute — and it does this regardless of whether other threads are blocked on any of these robust mutexes or not. like, nobody has to be waiting. it just runs high. main character behavior fr fr.

When a thread owns one or more non-robust mutexes initialized with the PTHREAD_PRIO_PROTECT protocol, it shall execute at the higher of its priority or the highest of the priority ceilings of all the non-robust mutexes owned by this thread and initialized with this attribute, regardless of whether other threads are blocked on any of these non-robust mutexes or not. yeah. same thing, non-robust version. I said what I said. 🎀

While a thread is holding a mutex which has been initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attributes, it shall not be subject to being moved to the tail of the scheduling queue at its priority in the event that its original priority is changed, such as by a call to sched_setparam(). Likewise, when a thread unlocks a mutex that has been initialized with the PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT protocol attributes, it shall not be subject to being moved to the tail of the scheduling queue at its priority in the event that its original priority is changed. no queue demotion for you, gorgeous. 🦋

If a thread simultaneously owns several mutexes initialized with different protocols, it shall execute at the highest of the priorities that it would have obtained by each of these protocols. pick the best one, obviously. ✨

When a thread makes a call to pthread_mutex_lock(), and the mutex was initialized with the protocol attribute having the value PTHREAD_PRIO_INHERIT, and the calling thread is blocked because the mutex is owned by another thread — that owner thread shall inherit the priority level of the calling thread as long as it continues to own the mutex. The implementation shall update its execution priority to the maximum of its assigned priority and all its inherited priorities. Furthermore, if this owner thread itself becomes blocked on another mutex with the protocol attribute having the value PTHREAD_PRIO_INHERIT, the same priority inheritance effect shall be propagated to this other owner thread, in a recursive manner. yes bestie it's a chain reaction, it's giving dominoes, it's giving generational priority. 🔥

⚠️ ok important one: The behavior is undefined if the value specified by the attr argument to pthread_mutexattr_getprotocol() or pthread_mutexattr_setprotocol() does not refer to an initialized mutex attributes object. undefined. we don't do that. 🙈

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💜 RETURN VALUE

Upon successful completion, the pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions shall return zero; otherwise, an error number shall be returned to indicate the error. slay when it's zero, sad when it's not. 😭

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💀 ERRORS

The pthread_mutexattr_setprotocol() function shall fail if:

• ENOTSUP — The value specified by protocol is an unsupported value. like, not in our roster, sorry babe.

The pthread_mutexattr_getprotocol() and pthread_mutexattr_setprotocol() functions may fail if:

• EINVAL — The value specified by protocol is invalid.
• EPERM — The caller does not have the privilege to perform the operation. no permission, no entry, no exceptions. 💅

These functions shall not return an error code of [EINTR].

The following sections are informative.

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🍓 EXAMPLES

None. (I know. I know. nothing to show off with here. 💀)

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🧚 APPLICATION USAGE

None. (also nothing. iconic of them honestly.)

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🌟 RATIONALE

If an implementation detects that the value specified by the attr argument to pthread_mutexattr_getprotocol() or pthread_mutexattr_setprotocol() does not refer to an initialized mutex attributes object, it is recommended that the function should fail and report an [EINVAL] error. (recommended, not required — that's the tea. 🫖)

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🔮 FUTURE DIRECTIONS

None. the future is... empty. very demure. very mindful. ✨

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👀 SEE ALSO

• pthread_cond_destroy()
• pthread_create()
• pthread_mutex_destroy()

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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okay that's the whole thing, bestie, no skips, no cuts. 🫶 this one's brought to you by IEEE and The Open Group, dated 2017 — go forth and inherit your priorities responsibly. mwah. 💖🎀🦋