From b2ab9910dd5f13ca2d92eeb4c39a90b922df8dfe Mon Sep 17 00:00:00 2001 From: Hallvard Furuseth Date: Sat, 17 Jan 2015 06:32:12 +0100 Subject: [PATCH] ITS#7971 Fix reader allocation and me_numreaders --- libraries/liblmdb/mdb.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c index e2aa170..7175276 100644 --- a/libraries/liblmdb/mdb.c +++ b/libraries/liblmdb/mdb.c @@ -1185,7 +1185,8 @@ struct MDB_env { unsigned int me_psize; /**< DB page size, inited from me_os_psize */ unsigned int me_os_psize; /**< OS page size, from #GET_PAGESIZE */ unsigned int me_maxreaders; /**< size of the reader table */ - unsigned int me_numreaders; /**< max numreaders set by this env */ + /** Max #MDB_txninfo.%mti_numreaders of interest to #mdb_env_close() */ + volatile int me_close_readers; MDB_dbi me_numdbs; /**< number of DBs opened */ MDB_dbi me_maxdbs; /**< size of the DB table */ MDB_PID_T me_pid; /**< process ID of this env */ @@ -2603,13 +2604,19 @@ mdb_txn_renew0(MDB_txn *txn) return MDB_READERS_FULL; } r = &ti->mti_readers[i]; + /* Claim the reader slot, carefully since other code + * uses the reader table un-mutexed: First reset the + * slot, next publish it in mti_numreaders. After + * that, it is safe for mdb_env_close() to touch it. + * When it will be closed, we can finally claim it. + */ + r->mr_pid = 0; r->mr_txnid = (txnid_t)-1; r->mr_tid = tid; - r->mr_pid = pid; /* should be written last, see ITS#7971. */ if (i == nr) ti->mti_numreaders = ++nr; - /* Save numreaders for un-mutexed mdb_env_close() */ - env->me_numreaders = nr; + env->me_close_readers = nr; + r->mr_pid = pid; UNLOCK_MUTEX(rmutex); new_notls = (env->me_flags & MDB_NOTLS); @@ -4790,8 +4797,12 @@ mdb_env_close0(MDB_env *env, int excl) MDB_PID_T pid = env->me_pid; /* Clearing readers is done in this function because * me_txkey with its destructor must be disabled first. + * + * We skip the the reader mutex, so we touch only + * data owned by this process (me_close_readers and + * our readers), and clear each reader atomically. */ - for (i = env->me_numreaders; --i >= 0; ) + for (i = env->me_close_readers; --i >= 0; ) if (env->me_txns->mti_readers[i].mr_pid == pid) env->me_txns->mti_readers[i].mr_pid = 0; #ifdef _WIN32 @@ -9110,11 +9121,7 @@ mdb_env_info(MDB_env *env, MDB_envinfo *arg) arg->me_mapaddr = env->me_metas[toggle]->mm_address; arg->me_mapsize = env->me_mapsize; arg->me_maxreaders = env->me_maxreaders; - - /* me_numreaders may be zero if this process never used any readers. Use - * the shared numreader count if it exists. - */ - arg->me_numreaders = env->me_txns ? env->me_txns->mti_numreaders : env->me_numreaders; + arg->me_numreaders = env->me_txns ? env->me_txns->mti_numreaders : 0; arg->me_last_pgno = env->me_metas[toggle]->mm_last_pg; arg->me_last_txnid = env->me_metas[toggle]->mm_txnid; -- 2.7.4