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ITS#8505 Clarify fork() caveat, mdb_env_get_fd(), flock->fcntl.

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This commit is contained in:
Hallvard Furuseth 2016-09-27 07:03:42 +02:00
parent 6e81d4071b
commit e911ad64b9
1 changed files with 7 additions and 2 deletions
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9
libraries/liblmdb/lmdb.h
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@ -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.