From 9a80a8a8e8feed56fbccd8851b8a789f7fff9c11 Mon Sep 17 00:00:00 2001
From: "leo@yuriev.ru" <leo@yuriev.ru>
Date: Fri, 17 Oct 2014 22:22:39 +0000
Subject: [PATCH] ITS#7969 LMDB: volatile & __synchronize().
Globally shared fields of meta-data are not 'volatile'.
---
libraries/liblmdb/mdb.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 9e65c2741d..c84c07f042 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -610,11 +610,11 @@ typedef struct MDB_rxbody {
* started from so we can avoid overwriting any data used in that
* particular version.
*/
- txnid_t mrb_txnid;
+ volatile txnid_t mrb_txnid;
/** The process ID of the process owning this reader txn. */
- MDB_PID_T mrb_pid;
+ volatile MDB_PID_T mrb_pid;
/** The thread ID of the thread owning this txn. */
- MDB_THR_T mrb_tid;
+ volatile MDB_THR_T mrb_tid;
} MDB_rxbody;
/** The actual reader record, with cacheline padding. */
@@ -664,12 +664,12 @@ typedef struct MDB_txbody {
* This is recorded here only for convenience; the value can always
* be determined by reading the main database meta pages.
*/
- txnid_t mtb_txnid;
+ volatile txnid_t mtb_txnid;
/** The number of slots that have been used in the reader table.
* This always records the maximum count, it is not decremented
* when readers release their slots.
*/
- unsigned mtb_numreaders;
+ volatile unsigned mtb_numreaders;
} MDB_txbody;
/** The actual reader table definition. */
@@ -942,7 +942,7 @@ typedef struct MDB_meta {
/** Any persistent environment flags. @ref mdb_env */
#define mm_flags mm_dbs[0].md_flags
pgno_t mm_last_pg; /**< last used page in file */
- txnid_t mm_txnid; /**< txnid that committed this page */
+ volatile txnid_t mm_txnid; /**< txnid that committed this page */
} MDB_meta;
/** Buffer for a stack-allocated meta page.
@@ -3601,6 +3601,10 @@ mdb_env_write_meta(MDB_txn *txn)
mp->mm_dbs[0] = txn->mt_dbs[0];
mp->mm_dbs[1] = txn->mt_dbs[1];
mp->mm_last_pg = txn->mt_next_pgno - 1;
+#if !(defined(_MSC_VER) || defined(__i386__) || defined(__x86_64__))
+ /* LY: issue a memory barrier, if not x86. ITS#7969 */
+ __sync_synchronize();
+#endif
mp->mm_txnid = txn->mt_txnid;
if (!(env->me_flags & (MDB_NOMETASYNC|MDB_NOSYNC))) {
unsigned meta_size = env->me_psize;
--
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