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mdbx: refine mdb_meta_head_r().

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Change-Id: I038862b3dada408de46f24175513d7522b1f89f5
This commit is contained in:
Leo Yuriev 2016-03-13 18:41:28 +03:00
parent 340da0fd7a
commit 4d9c0657d9
1 changed files with 29 additions and 39 deletions
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68
mdb.c
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@ -1883,54 +1883,44 @@ static MDB_meta* mdb_meta_head_w(MDB_env *env) {
return a;
}
static
MDB_meta* mdb_meta_head_r(MDB_env *env) {
static MDB_meta*
mdb_meta_head_r(MDB_env *env) {
MDB_meta* a = METAPAGE_1(env);
MDB_meta* b = METAPAGE_2(env), *h;
txnid_t head_txnid;
int loop = 0, rc;
while(1) {
#ifdef __SANITIZE_THREAD__
pthread_mutex_lock(&tsan_mutex);
#endif
head_txnid = env->me_txns->mti_txnid;
mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);
if (likely(a->mm_txnid == head_txnid)) {
#ifdef __SANITIZE_THREAD__
pthread_mutex_unlock(&tsan_mutex);
#endif
return a;
}
if (likely(b->mm_txnid == head_txnid)) {
#ifdef __SANITIZE_THREAD__
pthread_mutex_unlock(&tsan_mutex);
#endif
return b;
}
#ifdef __SANITIZE_THREAD__
pthread_mutex_unlock(&tsan_mutex);
pthread_mutex_lock(&tsan_mutex);
#endif
/* LY: got a race on env->me_txns->mti_txnid with mdb_env_sync0() */
#if defined(__i386__) || defined(__x86_64__)
__asm__ __volatile__("pause");
#endif
txnid_t head_txnid = env->me_txns->mti_txnid;
mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);
if (likely(a->mm_txnid == head_txnid)) {
h = a;
} else if (likely(b->mm_txnid == head_txnid)) {
h = b;
} else {
/* LY: seems got a race with mdb_env_sync0() */
mdb_coherent_barrier();
loop += 1;
if(likely(loop < 3))
continue;
if(unlikely(loop > 5))
break;
pthread_yield();
head_txnid = env->me_txns->mti_txnid;
mdb_assert(env, a->mm_txnid != b->mm_txnid || head_txnid == 0);
if (likely(a->mm_txnid == head_txnid)) {
h = a;
} else if (likely(b->mm_txnid == head_txnid)) {
h = b;
} else {
/* LY: got a race again, or DB is corrupted */
int rc = mdb_mutex_lock(env, MDB_MUTEX(env, w));
h = mdb_meta_head_w(env);
if (rc == 0)
mdb_mutex_unlock(env, MDB_MUTEX(env, w));
}
}
rc = mdb_mutex_lock(env, MDB_MUTEX(env, w));
h = mdb_meta_head_w(env);
if (rc == 0)
mdb_mutex_unlock(env, MDB_MUTEX(env, w));
#ifdef __SANITIZE_THREAD__
pthread_mutex_unlock(&tsan_mutex);
#endif
return h;
}