`pthread_rwlock_clockrdlock` / `pthread_rwlock_clockwrlock` (3) - glibc

Split from the chapter glibc: Threads into the per-function layout; see the method page and the glibc ledger for coverage status.

Field	Value
Header	`pthread.h` (rwlock block, `__USE_GNU` nested in `__USE_UNIX98
Standards	POSIX.1-2024 (manual standards note, Waiting with Explicit Clocks node; no separate man3 page in the cached man-pages set)
Exported	`pthread_rwlock_clockrdlock@@GLIBC_2.34` plus compat `@GLIBC_2.30`; `pthread_rwlock_clockwrlock@@GLIBC_2.34` plus compat `@GLIBC_2.30` (nm, host glibc 2.41); 64-bit-time redirects `__pthread_rwlock_clock{rd,wr}lock64`
Thread-safety	MT-Safe (manual safety notes: `@asulock`, `@aculock`)
Ledger ID	GLIBC-pthread_rwlock_clockrdlock, GLIBC-pthread_rwlock_clockwrlock

Declaration and gates

#include <pthread.h>

int pthread_rwlock_clockrdlock(pthread_rwlock_t *restrict rwlock,
                               clockid_t clockid,
                               const struct timespec *restrict abstime);
                                                         /* :1004 */
int pthread_rwlock_clockwrlock(pthread_rwlock_t *restrict rwlock,
                               clockid_t clockid,
                               const struct timespec *restrict abstime);
                                                         /* :1051 */

Both are guarded by #ifdef __USE_GNU inside the rwlock block opened by #if defined __USE_UNIX98 || defined __USE_XOPEN2K (/usr/include/pthread.h line 961; clock variants at 1004-1020 and 1051-1067). The base rwlock family is covered in pthread-rwlock-family.

Semantics

Both behave like pthread_rwlock_timedrdlock / pthread_rwlock_timedwrlock except that the absolute timeout abstime is measured against the clock named by clockid instead of the CLOCK_REALTIME default of the timed variants (manual, Waiting with Explicit Clocks). Currently clockid must be CLOCK_MONOTONIC or CLOCK_REALTIME, and any other value makes the call fail with EINVAL (manual, both entries). Everything else – reader/writer acquisition rules, blocking – is the timed rwlock behavior the manual references.

Gotchas and portability

The motivating use is timeout arithmetic: measure deadlines against CLOCK_MONOTONIC so real-time clock adjustments cannot shrink or stretch a wait.
Adopted by POSIX.1-2024 like the other explicit-clock waits (pthread_cond_clockwait, sem_clockwait), but glibc still gates the prototypes behind _GNU_SOURCE.
musl 1.2.5: absent – musl src/thread/ has the plain and timed rwlock calls only, no *clock* variants.

Errors

EINVAL: clockid is neither CLOCK_MONOTONIC nor CLOCK_REALTIME (manual, Waiting with Explicit Clocks). Errors of the underlying timed acquisition are not enumerated on the clock variants in the cached manual.

References

glibc manual: threads.texi, node Waiting with Explicit Clocks
header: /usr/include/pthread.h lines 961, 1004-1020, 1051-1067
symbols: nm -D --with-symbol-versions libc.so.6

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