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Commit f7aa0d5e authored by Howard Chu's avatar Howard Chu
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Tweak locks, fix race conditions

parent d27a7754
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libraries/libmdb/mdb.c
View file @ f7aa0d5e
......@@ -91,6 +91,32 @@ typedef ULONG pgno_t;
#define DKEY(x)
#endif
/* The DB view is always consistent because all writes are wrapped in
* the wmutex. Finer-grained locks aren't necessary.
*/
#ifndef LAZY_LOCKS
#define LAZY_LOCKS 1
#endif
#if LAZY_LOCKS
#define LAZY_MUTEX_LOCK(x)
#define LAZY_MUTEX_UNLOCK(x)
#define LAZY_RWLOCK_UNLOCK(x)
#define LAZY_RWLOCK_WRLOCK(x)
#define LAZY_RWLOCK_RDLOCK(x)
#define LAZY_RWLOCK_DEF(x)
#define LAZY_RWLOCK_INIT(x,y)
#define LAZY_RWLOCK_DESTROY(x)
#else
#define LAZY_MUTEX_LOCK(x) pthread_mutex_lock(x)
#define LAZY_MUTEX_UNLOCK(x) pthread_mutex_unlock(x)
#define LAZY_RWLOCK_UNLOCK(x) pthread_rwlock_unlock(x)
#define LAZY_RWLOCK_WRLOCK(x) pthread_rwlock_wrlock(x)
#define LAZY_RWLOCK_RDLOCK(x) pthread_rwlock_rdlock(x)
#define LAZY_RWLOCK_DEF(x) pthread_rwlock_t x
#define LAZY_RWLOCK_INIT(x,y) pthread_rwlock_init(x,y)
#define LAZY_RWLOCK_DESTROY(x) pthread_rwlock_destroy(x)
#endif
#define P_INVALID (~0UL)
#define F_ISSET(w, f) (((w) & (f)) == (f))
......@@ -308,8 +334,8 @@ struct MDB_txn {
#define MDB_TXN_RDONLY 0x01 /* read-only transaction */
#define MDB_TXN_ERROR 0x02 /* an error has occurred */
#define MDB_TXN_METOGGLE 0x04 /* used meta page 1 */
unsigned int mt_flags;
unsigned int mt_toggle;
};
/* Context for sorted-dup records */
......@@ -334,7 +360,6 @@ struct MDB_env {
char *me_map;
MDB_txninfo *me_txns;
MDB_meta *me_metas[2];
MDB_meta *me_meta;
MDB_txn *me_txn; /* current write transaction */
size_t me_mapsize;
off_t me_size; /* current file size */
......@@ -348,6 +373,7 @@ struct MDB_env {
MDB_dpage *me_dpages;
pgno_t me_free_pgs[MDB_IDL_UM_SIZE];
MIDL2 me_dirty_list[MDB_IDL_DB_SIZE];
LAZY_RWLOCK_DEF(me_dblock);
};
#define NODESIZE offsetof(MDB_node, mn_data)
......@@ -714,8 +740,6 @@ mdb_txn_renew0(MDB_txn *txn)
{
MDB_env *env = txn->mt_env;
int rc, toggle;
if (env->me_flags & MDB_FATAL_ERROR) {
DPUTS("mdb_txn_begin: environment had fatal error, must shutdown!");
return MDB_PANIC;
......@@ -725,6 +749,9 @@ mdb_txn_renew0(MDB_txn *txn)
MDB_reader *r = pthread_getspecific(env->me_txkey);
if (!r) {
unsigned int i;
pid_t pid = getpid();
pthread_t tid = pthread_self();
pthread_mutex_lock(&env->me_txns->mti_mutex);
for (i=0; i<env->me_txns->mti_numreaders; i++)
if (env->me_txns->mti_readers[i].mr_pid == 0)
......@@ -733,47 +760,40 @@ mdb_txn_renew0(MDB_txn *txn)
pthread_mutex_unlock(&env->me_txns->mti_mutex);
return ENOSPC;
}
env->me_txns->mti_readers[i].mr_pid = getpid();
env->me_txns->mti_readers[i].mr_tid = pthread_self();
r = &env->me_txns->mti_readers[i];
pthread_setspecific(env->me_txkey, r);
env->me_txns->mti_readers[i].mr_pid = pid;
env->me_txns->mti_readers[i].mr_tid = tid;
if (i >= env->me_txns->mti_numreaders)
env->me_txns->mti_numreaders = i+1;
pthread_mutex_unlock(&env->me_txns->mti_mutex);
r = &env->me_txns->mti_readers[i];
pthread_setspecific(env->me_txkey, r);
}
txn->mt_txnid = env->me_txns->mti_txnid;
txn->mt_toggle = env->me_txns->mti_me_toggle;
r->mr_txnid = txn->mt_txnid;
txn->mt_u.reader = r;
} else {
pthread_mutex_lock(&env->me_txns->mti_wmutex);
txn->mt_txnid = env->me_txns->mti_txnid+1;
txn->mt_toggle = env->me_txns->mti_me_toggle;
txn->mt_u.dirty_list = env->me_dirty_list;
txn->mt_u.dirty_list[0].mid = 0;
txn->mt_free_pgs = env->me_free_pgs;
txn->mt_free_pgs[0] = 0;
txn->mt_next_pgno = env->me_metas[txn->mt_toggle]->mm_last_pg+1;
env->me_txn = txn;
}
toggle = env->me_txns->mti_me_toggle;
if ((rc = mdb_env_read_meta(env, &toggle)) != MDB_SUCCESS) {
mdb_txn_reset0(txn);
return rc;
}
/* Copy the DB arrays */
LAZY_RWLOCK_RDLOCK(&env->me_dblock);
txn->mt_numdbs = env->me_numdbs;
txn->mt_dbxs = env->me_dbxs; /* mostly static anyway */
memcpy(txn->mt_dbs, env->me_meta->mm_dbs, 2 * sizeof(MDB_db));
memcpy(txn->mt_dbs, env->me_metas[txn->mt_toggle]->mm_dbs, 2 * sizeof(MDB_db));
if (txn->mt_numdbs > 2)
memcpy(txn->mt_dbs+2, env->me_dbs[env->me_db_toggle]+2,
(txn->mt_numdbs - 2) * sizeof(MDB_db));
if (!(txn->mt_flags & MDB_TXN_RDONLY)) {
if (toggle)
txn->mt_flags |= MDB_TXN_METOGGLE;
txn->mt_next_pgno = env->me_meta->mm_last_pg+1;
}
LAZY_RWLOCK_UNLOCK(&env->me_dblock);
DPRINTF("begin txn %p %lu%c on mdbenv %p, root page %lu", txn,
txn->mt_txnid, (txn->mt_flags & MDB_TXN_RDONLY) ? 'r' : 'w',
......@@ -1075,16 +1095,21 @@ mdb_txn_commit(MDB_txn *txn)
return n;
}
env->me_txns->mti_txnid = txn->mt_txnid;
done:
env->me_txn = NULL;
/* update the DB tables */
{
int toggle = !env->me_db_toggle;
MDB_db *ip, *jp;
for (i = 2; i < txn->mt_numdbs; i++)
env->me_dbs[toggle][i] = txn->mt_dbs[i];
ip = &env->me_dbs[toggle][2];
jp = &txn->mt_dbs[2];
LAZY_RWLOCK_WRLOCK(&env->me_dblock);
for (i = 2; i < txn->mt_numdbs; i++) {
if (ip->md_root != jp->md_root)
*ip = *jp;
ip++; jp++;
}
for (i = 2; i < txn->mt_numdbs; i++) {
if (txn->mt_dbxs[i].md_dirty)
......@@ -1092,6 +1117,7 @@ done:
}
env->me_db_toggle = toggle;
env->me_numdbs = txn->mt_numdbs;
LAZY_RWLOCK_UNLOCK(&env->me_dblock);
}
pthread_mutex_unlock(&env->me_txns->mti_wmutex);
......@@ -1197,7 +1223,7 @@ mdb_env_write_meta(MDB_txn *txn)
assert(txn != NULL);
assert(txn->mt_env != NULL);
toggle = !F_ISSET(txn->mt_flags, MDB_TXN_METOGGLE);
toggle = !txn->mt_toggle;
DPRINTF("writing meta page %d for root page %lu",
toggle, txn->mt_dbs[MAIN_DBI].md_root);
......@@ -1236,7 +1262,16 @@ mdb_env_write_meta(MDB_txn *txn)
env->me_flags |= MDB_FATAL_ERROR;
return rc;
}
/* Memory ordering issues are irrelevant; since the entire writer
* is wrapped by wmutex, all of these changes will become visible
* after the wmutex is unlocked. Since the DB is multi-version,
* readers will get consistent data regardless of how fresh or
* how stale their view of these values is.
*/
LAZY_MUTEX_LOCK(&env->me_txns->mti_mutex);
txn->mt_env->me_txns->mti_me_toggle = toggle;
txn->mt_env->me_txns->mti_txnid = txn->mt_txnid;
LAZY_MUTEX_UNLOCK(&env->me_txns->mti_mutex);
return MDB_SUCCESS;
}
......@@ -1248,15 +1283,11 @@ mdb_env_read_meta(MDB_env *env, int *which)
assert(env != NULL);
if (which)
toggle = *which;
else if (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid)
if (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid)
toggle = 1;
if (env->me_meta != env->me_metas[toggle])
env->me_meta = env->me_metas[toggle];
DPRINTF("Using meta page %d", toggle);
*which = toggle;
return MDB_SUCCESS;
}
......@@ -1313,7 +1344,7 @@ mdb_env_get_maxreaders(MDB_env *env, int *readers)
static int
mdb_env_open2(MDB_env *env, unsigned int flags)
{
int i, newenv = 0;
int i, newenv = 0, toggle;
MDB_meta meta;
MDB_page *p;
......@@ -1358,17 +1389,17 @@ mdb_env_open2(MDB_env *env, unsigned int flags)
env->me_metas[0] = METADATA(p);
env->me_metas[1] = (MDB_meta *)((char *)env->me_metas[0] + meta.mm_psize);
if ((i = mdb_env_read_meta(env, NULL)) != 0)
if ((i = mdb_env_read_meta(env, &toggle)) != 0)
return i;
DPRINTF("opened database version %u, pagesize %u",
env->me_meta->mm_version, env->me_psize);
DPRINTF("depth: %u", env->me_meta->mm_dbs[MAIN_DBI].md_depth);
DPRINTF("entries: %lu", env->me_meta->mm_dbs[MAIN_DBI].md_entries);
DPRINTF("branch pages: %lu", env->me_meta->mm_dbs[MAIN_DBI].md_branch_pages);
DPRINTF("leaf pages: %lu", env->me_meta->mm_dbs[MAIN_DBI].md_leaf_pages);
DPRINTF("overflow pages: %lu", env->me_meta->mm_dbs[MAIN_DBI].md_overflow_pages);
DPRINTF("root: %lu", env->me_meta->mm_dbs[MAIN_DBI].md_root);
env->me_metas[toggle]->mm_version, env->me_psize);
DPRINTF("depth: %u", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_depth);
DPRINTF("entries: %lu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_entries);
DPRINTF("branch pages: %lu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_branch_pages);
DPRINTF("leaf pages: %lu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_leaf_pages);
DPRINTF("overflow pages: %lu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_overflow_pages);
DPRINTF("root: %lu", env->me_metas[toggle]->mm_dbs[MAIN_DBI].md_root);
return MDB_SUCCESS;
}
......@@ -1388,10 +1419,12 @@ static void
mdb_env_share_locks(MDB_env *env)
{
struct flock lock_info;
int toggle = 0;
env->me_txns->mti_txnid = env->me_meta->mm_txnid;
if (env->me_metas[0]->mm_txnid < env->me_metas[1]->mm_txnid)
env->me_txns->mti_me_toggle = 1;
toggle = 1;
env->me_txns->mti_me_toggle = toggle;
env->me_txns->mti_txnid = env->me_metas[toggle]->mm_txnid;
memset((void *)&lock_info, 0, sizeof(lock_info));
lock_info.l_type = F_RDLCK;
......@@ -1535,6 +1568,7 @@ mdb_env_open(MDB_env *env, const char *path, unsigned int flags, mode_t mode)
env->me_path = strdup(path);
DPRINTF("opened dbenv %p", (void *) env);
pthread_key_create(&env->me_txkey, mdb_env_reader_dest);
LAZY_RWLOCK_INIT(&env->me_dblock, NULL);
if (excl)
mdb_env_share_locks(env);
env->me_dbxs = calloc(env->me_maxdbs, sizeof(MDB_dbx));
......@@ -1577,6 +1611,7 @@ mdb_env_close(MDB_env *env)
free(env->me_dbxs);
free(env->me_path);
LAZY_RWLOCK_DESTROY(&env->me_dblock);
pthread_key_delete(env->me_txkey);
if (env->me_map) {
......@@ -1587,7 +1622,7 @@ mdb_env_close(MDB_env *env)
if (env->me_txns) {
pid_t pid = getpid();
size_t size = (env->me_maxreaders-1) * sizeof(MDB_reader) + sizeof(MDB_txninfo);
int i;
unsigned int i;
for (i=0; i<env->me_txns->mti_numreaders; i++)
if (env->me_txns->mti_readers[i].mr_pid == pid)
env->me_txns->mti_readers[i].mr_pid = 0;
......@@ -1718,7 +1753,7 @@ mdb_get_page(MDB_txn *txn, pgno_t pgno, MDB_page **ret)
}
}
if (!p) {
if (pgno <= txn->mt_env->me_meta->mm_last_pg)
if (pgno <= txn->mt_env->me_metas[txn->mt_toggle]->mm_last_pg)
p = (MDB_page *)(txn->mt_env->me_map + txn->mt_env->me_psize * pgno);
}
*ret = p;
......@@ -3674,10 +3709,14 @@ mdb_stat0(MDB_env *env, MDB_db *db, MDB_stat *arg)
int
mdb_env_stat(MDB_env *env, MDB_stat *arg)
{
int toggle;
if (env == NULL || arg == NULL)
return EINVAL;
return mdb_stat0(env, &env->me_meta->mm_dbs[MAIN_DBI], arg);
mdb_env_read_meta(env, &toggle);
return mdb_stat0(env, &env->me_metas[toggle]->mm_dbs[MAIN_DBI], arg);
}
int mdb_open(MDB_txn *txn, const char *name, unsigned int flags, MDB_dbi *dbi)
......
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