pthread_rwlock_timedrdlock(3) on FreeBSD
The text 496ced5041f1, as FreeBSD 6.3-RELEASE, FreeBSD 6.2-RELEASE, FreeBSD 6.1-RELEASE, FreeBSD 6.0-RELEASE, FreeBSD 5.5-RELEASE, FreeBSD 5.4-RELEASE, FreeBSD 5.3-RELEASE shipped it.
acquire a read-write lock for reading or give up after a specified period