On 2014-06-26 00:08:48 +0300, Heikki Linnakangas wrote: > LWLocks are implemented with semaphores, so if you can increment a semaphore > in the signal handler / callback thread, then in theory you should be able > to release a LWLock.
I don't think that's a convincing argument even if semop et al were signal safe. LWLocks also use spinlocks and it's a fairly bad idea to do anything with the same spinlock both inside and outside a signal handler. I don't think we're going to get lwlock.c/LWLockRelease to work reasonably from a signal handler without a lot of work. > On Linux at least we use System V semaphores, which are (unsurpisingly) not > listed as safe for using in a signal handler. See list Async-signal-safe > functions in signal(7) man page. The function used to increment a POSIX > semaphore, sem_post(), is in the list, however. Heh, just wrote the same after reading the beginning of your email ;) Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
