From e911ad64b905dc6532270b2de5f7cb46e80167b4 Mon Sep 17 00:00:00 2001 From: Hallvard Furuseth Date: Tue, 27 Sep 2016 07:03:42 +0200 Subject: [PATCH] ITS#8505 Clarify fork() caveat, mdb_env_get_fd(), flock->fcntl. --- libraries/liblmdb/lmdb.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/libraries/liblmdb/lmdb.h b/libraries/liblmdb/lmdb.h index a356538..ba74a22 100644 --- a/libraries/liblmdb/lmdb.h +++ b/libraries/liblmdb/lmdb.h @@ -96,11 +96,12 @@ * transactions. Each transaction belongs to one thread. See below. * The #MDB_NOTLS flag changes this for read-only transactions. * - * - Use an MDB_env* in the process which opened it, without fork()ing. + * - Use an MDB_env* in the process which opened it, not after fork(). * * - Do not have open an LMDB database twice in the same process at * the same time. Not even from a plain open() call - close()ing it - * breaks flock() advisory locking. + * breaks fcntl() advisory locking. (It is OK to reopen it after + * fork() - exec*(), since the lockfile has FD_CLOEXEC set.) * * - Avoid long-lived transactions. Read transactions prevent * reuse of pages freed by newer write transactions, thus the @@ -794,6 +795,10 @@ int mdb_env_get_flags(MDB_env *env, unsigned int *flags); int mdb_env_get_path(MDB_env *env, const char **path); /** @brief Return the filedescriptor for the given environment. + * + * This function may be called after fork(), so the descriptor can be + * closed before exec*(). Other LMDB file descriptors have FD_CLOEXEC. + * (Until LMDB 0.9.18, only the lockfile had that.) * * @param[in] env An environment handle returned by #mdb_env_create() * @param[out] fd Address of a mdb_filehandle_t to contain the descriptor.