PTHREAD_BARRIER_WAIT(3P)

💖 PTHREAD_BARRIER_WAIT(3P) 💖

okay so bestie, welcome to the POSIX Programmer's Manual ✨ this page is literally part of it, no cap. 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 honestly the interface may not even be implemented on Linux at all. it's giving "check your platform first" 🫶

---

🌸 NAME 🌸

pthread_barrier_wait — synchronize at a barrier

---

🎀 SYNOPSIS 🎀

#include <pthread.h>

int pthread_barrier_wait(pthread_barrier_t *barrier);

---

✨ DESCRIPTION ✨

so pthread_barrier_wait() shall synchronize the participating threads at the barrier referenced by barrier. the calling thread shall block until the required number of threads have called pthread_barrier_wait() specifying that same barrier. it's giving "we're all waiting for the group chat to be complete before we go" 💅

when the required number of threads have called pthread_barrier_wait() specifying the barrier, the constant PTHREAD_BARRIER_SERIAL_THREAD shall be returned to one unspecified thread and zero shall be returned to each of the remaining threads. and at this point? the barrier shall be reset to the state it had as a result of the most recent pthread_barrier_init() function that referenced it. iconic behavior honestly 🌈

the constant PTHREAD_BARRIER_SERIAL_THREAD is defined in <pthread.h> and its value shall be distinct from any other value returned by pthread_barrier_wait(). so like, no identity crises, it's one of a kind 👑

⚠️ the results are undefined if this function is called with an uninitialized barrier. literally do not do that. not the vibe. 💀

if a signal is delivered to a thread blocked on a barrier, upon return from the signal handler the thread shall resume waiting at the barrier if the barrier wait has not completed (that is, if the required number of threads have not arrived at the barrier during the execution of the signal handler); otherwise, the thread shall continue as normal from the completed barrier wait. and until the thread in the signal handler returns from it, it is unspecified whether other threads may proceed past the barrier once they have all reached it. messy? a little. correct? yes. 🧚

a thread that has blocked on a barrier shall not prevent any unblocked thread that is eligible to use the same processing resources from eventually making forward progress in its execution. eligibility for processing resources shall be determined by the scheduling policy. everyone gets their moment, periodt ✋

---

💜 RETURN VALUE 💜

upon successful completion, the pthread_barrier_wait() function shall return PTHREAD_BARRIER_SERIAL_THREAD for a single (arbitrary) thread synchronized at the barrier and zero for each of the other threads. otherwise, an error number shall be returned to indicate the error. so like, one main character and a whole supporting cast 🎬

---

🔥 ERRORS 🔥

this function shall not return an error code of [EINTR]. nope. not happening. 🙈

the following sections are informative.

---

🍓 EXAMPLES 🍓

None.

---

🦋 APPLICATION USAGE 🦋

applications using this function may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion. yeah, that's a thing, and it's mentioned right there 💫

---

⭐ RATIONALE ⭐

if an implementation detects that the value specified by the barrier argument to pthread_barrier_wait() does not refer to an initialized barrier object, it is recommended that the function should fail and report an [EINVAL] error. like, recommended. take the hint bestie 🫶

---

🌈 FUTURE DIRECTIONS 🌈

None.

---

👑 SEE ALSO 👑

• pthread_barrier_destroy()
• the Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion
• the Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory Synchronization
• <pthread.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 thing, bestie 🎀 this page came to you from IEEE/The Open Group, dated 2017 — thanks for reading, ily, go synchronize those threads responsibly 💅✨