PTHREAD_GETSCHEDPARAM(3P)

🌸 PROLOG 🌸

ok so real talk bestie, this page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go check the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface may not even be implemented on Linux at all. 🙈

---

✨ NAME ✨

pthread_getschedparam, pthread_setschedparam — dynamic thread scheduling parameters access (REALTIME THREADS)

---

💅 SYNOPSIS 💅

#include <pthread.h>

int pthread_getschedparam(pthread_t thread, int *restrict policy,
    struct sched_param *restrict param);
int pthread_setschedparam(pthread_t thread, int policy,
    const struct sched_param *param);

---

🦋 DESCRIPTION 🦋

Okay so pthread_getschedparam() and pthread_setschedparam() do the thing where they get and set the scheduling policy and parameters of individual threads inside a multi-threaded process. Iconic behavior honestly. For SCHED_FIFO and SCHED_RR, the only member of the sched_param structure you're required to have is the priority, sched_priority. For SCHED_OTHER? The affected scheduling parameters are implementation-defined, iykyk. 🤷

The pthread_getschedparam() function shall retrieve the scheduling policy and scheduling parameters for the thread whose thread ID is given by thread, and shall store those values in policy and param, respectively. And listen — the priority value you get back from pthread_getschedparam() shall be the value specified by the most recent pthread_setschedparam(), pthread_setschedprio(), or pthread_create() call that affected the target thread. It shall not reflect any temporary adjustments to its priority that happened because of any priority inheritance or ceiling functions. Periodt. 💅

The pthread_setschedparam() function shall set the scheduling policy and associated scheduling parameters for the thread whose thread ID is given by thread to the policy and associated parameters provided in policy and param, respectively.

So the policy parameter may have the value SCHED_OTHER, SCHED_FIFO, or SCHED_RR. The scheduling parameters for the SCHED_OTHER policy are implementation-defined. The SCHED_FIFO and SCHED_RR policies shall have a single scheduling parameter: priority. ✨

If _POSIX_THREAD_SPORADIC_SERVER is defined, then the policy argument may have the value SCHED_SPORADIC, with the exception for the pthread_setschedparam() function that if the scheduling policy was not SCHED_SPORADIC at the time of the call, it is implementation-defined whether the function is supported — in other words, the implementation need not allow the application to dynamically change the scheduling policy to SCHED_SPORADIC. The sporadic server scheduling policy has the associated parameters sched_ss_low_priority, sched_ss_repl_period, sched_ss_init_budget, sched_priority, and sched_ss_max_repl.

The specified sched_ss_repl_period shall be greater than or equal to the specified sched_ss_init_budget for the function to succeed; if it is not, then the function shall fail. 😭 The value of sched_ss_max_repl shall be within the inclusive range [1,{SS_REPL_MAX}] for the function to succeed; if not, the function shall fail. And it is unspecified whether the sched_ss_repl_period and sched_ss_init_budget values are stored as provided by this function or are rounded to align with the resolution of the clock being used. 🕰️

If the pthread_setschedparam() function fails, the scheduling parameters shall not be changed for the target thread. No half-done glow-ups around here. 🚫

---

🫶 RETURN VALUE 🫶

If successful, the pthread_getschedparam() and pthread_setschedparam() functions shall return zero; otherwise, an error number shall be returned to indicate the error. slay. ✨

---

👑 ERRORS 👑

The pthread_setschedparam() function shall fail if:

• ENOTSUP — an attempt was made to set the policy or scheduling parameters to an unsupported value.
• ENOTSUP — an attempt was made to dynamically change the scheduling policy to SCHED_SPORADIC, and the implementation does not support this change.

The pthread_setschedparam() function may fail if:

• EINVAL — the value specified by policy or one of the scheduling parameters associated with the scheduling policy policy is invalid.
• EPERM — the caller does not have appropriate privileges to set either the scheduling parameters or the scheduling policy of the specified thread.
• EPERM — the implementation does not allow the application to modify one of the parameters to the value specified.

These functions shall not return an error code of [EINTR]. Not even once. 🚫

The following sections are informative.

---

🎀 EXAMPLES 🎀

None. (i know. tragic. but that's what it says bestie 😭)

---

🌈 APPLICATION USAGE 🌈

None. (again. nothing. we move. 💅)

---

🧚 RATIONALE 🧚

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. Like, expired thread ID? ghosted. 👻

---

⭐ FUTURE DIRECTIONS ⭐

None.

---

🔥 SEE ALSO 🔥

• pthread_setschedprio()
• sched_getparam()
• sched_getscheduler()

The Base Definitions volume of POSIX.1‐2017, <pthread.h>, <sched.h>

---

💖 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 .

---

and that's the whole page bestie!! 💖✨ this one came to you from IEEE/The Open Group, dated 2017, for PTHREAD_GETSCHEDPARAM(3P) — go forth and schedule those threads responsibly, mwah 🎀🦋💅