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authorRickard Green <[email protected]>2010-12-16 12:10:23 +0100
committerRickard Green <[email protected]>2010-12-16 12:12:25 +0100
commit46d9d4c36e1a9d52256b49d6fe6e519fc54a0f6e (patch)
treea854e8b80841980e600f3b3497717254c6e107b9
parent8b18824e2b13e60fb1a067f80dbb228172f6a3d2 (diff)
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Stop using reference counter when write accessing ETS-tables
-rw-r--r--erts/emulator/beam/erl_db.c136
-rw-r--r--erts/emulator/beam/erl_db_util.h5
2 files changed, 61 insertions, 80 deletions
diff --git a/erts/emulator/beam/erl_db.c b/erts/emulator/beam/erl_db.c
index e662b17592..6f19acdc3b 100644
--- a/erts/emulator/beam/erl_db.c
+++ b/erts/emulator/beam/erl_db.c
@@ -219,43 +219,34 @@ Export ets_select_continue_exp;
* Static traps
*/
static Export ets_delete_continue_exp;
-
-static ERTS_INLINE DbTable* db_ref(DbTable* tb, db_lock_kind_t kind)
-{
- if (tb != NULL && kind != LCK_READ) {
- erts_refc_inc(&tb->common.ref, 2);
- }
- return tb;
-}
static void
free_dbtable(DbTable* tb)
{
#ifdef HARDDEBUG
if (erts_smp_atomic_read(&tb->common.memory_size) != sizeof(DbTable)) {
- erts_fprintf(stderr, "ets: db_unref memory remain=%ld fix=%x\n",
- erts_smp_atomic_read(&tb->common.memory_size)-sizeof(DbTable),
+ erts_fprintf(stderr, "ets: free_dbtable memory remain=%ld fix=%x\n",
+ erts_smp_atomic_read(&tb->common.memory_size)-sizeof(DbTable),
tb->common.fixations);
}
- erts_fprintf(stderr, "ets: db_unref(%T) deleted!!!\r\n",
+ erts_fprintf(stderr, "ets: free_dbtable(%T) deleted!!!\r\n",
tb->common.id);
- erts_fprintf(stderr, "ets: db_unref: meta_pid_to_tab common.memory_size = %ld\n",
+ erts_fprintf(stderr, "ets: free_dbtable: meta_pid_to_tab common.memory_size = %ld\n",
erts_smp_atomic_read(&meta_pid_to_tab->common.memory_size));
print_table(ERTS_PRINT_STDOUT, NULL, 1, meta_pid_to_tab);
- erts_fprintf(stderr, "ets: db_unref: meta_pid_to_fixed_tab common.memory_size = %ld\n",
+ erts_fprintf(stderr, "ets: free_dbtable: meta_pid_to_fixed_tab common.memory_size = %ld\n",
erts_smp_atomic_read(&meta_pid_to_fixed_tab->common.memory_size));
print_table(ERTS_PRINT_STDOUT, NULL, 1, meta_pid_to_fixed_tab);
-
#endif
#ifdef ERTS_SMP
erts_smp_rwmtx_destroy(&tb->common.rwlock);
erts_smp_mtx_destroy(&tb->common.fixlock);
#endif
ASSERT(is_immed(tb->common.heir_data));
- erts_db_free(ERTS_ALC_T_DB_TABLE, tb, (void *) tb, sizeof(DbTable));
+ erts_db_free(ERTS_ALC_T_DB_TABLE, tb, (void *) tb, sizeof(DbTable));
ERTS_ETS_MISC_MEM_ADD(-sizeof(DbTable));
}
@@ -270,26 +261,26 @@ chk_free_dbtable(void *vtb)
}
#endif
-static ERTS_INLINE DbTable* db_unref(DbTable* tb, db_lock_kind_t kind)
+static void schedule_free_dbtable(DbTable* tb)
{
- if (kind != LCK_READ && erts_refc_dectest(&tb->common.ref, 0) == 0) {
+ /*
+ * NON-SMP case: Caller is *not* allowed to access the *tb
+ * structure after this function has returned!
+ * SMP case: Caller is allowed to access the *tb structure
+ * until the bif has returned (we typically
+ * need to unlock the table lock after this
+ * function has returned).
+ */
#ifdef ERTS_SMP
- int scheds = erts_get_max_no_executing_schedulers();
- if (scheds == 1)
- free_dbtable(tb);
- else {
- int refs = scheds - 1;
- ASSERT(scheds > 1);
- ERTS_THR_MEMORY_BARRIER;
- erts_refc_add(&tb->common.ref, refs, refs);
- erts_smp_schedule_misc_aux_work(1, scheds, chk_free_dbtable, tb);
- }
+ int scheds = erts_get_max_no_executing_schedulers();
+ ASSERT(scheds >= 1);
+ ASSERT(erts_refc_read(&tb->common.ref, 0) == 0);
+ erts_refc_init(&tb->common.ref, scheds);
+ ERTS_THR_MEMORY_BARRIER;
+ erts_smp_schedule_misc_aux_work(0, scheds, chk_free_dbtable, tb);
#else
- free_dbtable(tb);
+ free_dbtable(tb);
#endif
- return NULL;
- }
- return tb;
}
static ERTS_INLINE void db_init_lock(DbTable* tb, int use_frequent_read_lock,
@@ -300,8 +291,6 @@ static ERTS_INLINE void db_init_lock(DbTable* tb, int use_frequent_read_lock,
if (use_frequent_read_lock)
rwmtx_opt.type = ERTS_SMP_RWMTX_TYPE_FREQUENT_READ;
#endif
- erts_refc_init(&tb->common.ref, 1);
- erts_refc_init(&tb->common.fixref, 0);
#ifdef ERTS_SMP
erts_smp_rwmtx_init_opt_x(&tb->common.rwlock, &rwmtx_opt,
rwname, tb->common.the_name);
@@ -310,7 +299,7 @@ static ERTS_INLINE void db_init_lock(DbTable* tb, int use_frequent_read_lock,
#endif
}
-static ERTS_INLINE void db_lock_take_over_ref(DbTable* tb, db_lock_kind_t kind)
+static ERTS_INLINE void db_lock(DbTable* tb, db_lock_kind_t kind)
{
#ifdef ERTS_SMP
ASSERT(tb != meta_pid_to_tab && tb != meta_pid_to_fixed_tab);
@@ -338,16 +327,13 @@ static ERTS_INLINE void db_lock_take_over_ref(DbTable* tb, db_lock_kind_t kind)
#endif
}
-static ERTS_INLINE void db_lock(DbTable* tb, db_lock_kind_t kind)
-{
- (void) db_ref(tb, kind);
-#ifdef ERTS_SMP
- db_lock_take_over_ref(tb, kind);
-#endif
-}
-
static ERTS_INLINE void db_unlock(DbTable* tb, db_lock_kind_t kind)
{
+ /*
+ * In NON-SMP case tb may refer to an already deallocated
+ * DbTable structure. That is, ONLY the SMP case is allowed
+ * to follow the tb pointer!
+ */
#ifdef ERTS_SMP
ASSERT(tb != meta_pid_to_tab && tb != meta_pid_to_fixed_tab);
@@ -374,7 +360,6 @@ static ERTS_INLINE void db_unlock(DbTable* tb, db_lock_kind_t kind)
}
}
#endif
- (void) db_unref(tb, kind); /* May delete table... */
}
@@ -401,6 +386,13 @@ DbTable* db_get_table_aux(Process *p,
DbTable *tb = NULL;
erts_smp_rwmtx_t *mtl = NULL;
+ /*
+ * IMPORTANT: Only scheduler threads are allowed
+ * to access tables. Memory management
+ * depend on it.
+ */
+ ASSERT(erts_get_scheduler_data());
+
if (is_small(id)) {
Uint slot = unsigned_val(id) & meta_main_tab_slot_mask;
if (!meta_already_locked) {
@@ -414,12 +406,8 @@ DbTable* db_get_table_aux(Process *p,
|| erts_lc_rwmtx_is_rwlocked(test_mtl));
}
#endif
- if (slot < db_max_tabs && IS_SLOT_ALIVE(slot)) {
- /* SMP: inc to prevent race, between unlock of meta_main_tab_lock
- * and the table locking outside the meta_main_tab_lock
- */
- tb = db_ref(meta_main_tab[slot].u.tb, kind);
- }
+ if (slot < db_max_tabs && IS_SLOT_ALIVE(slot))
+ tb = meta_main_tab[slot].u.tb;
}
else if (is_atom(id)) {
struct meta_name_tab_entry* bucket = meta_name_tab_bucket(id,&mtl);
@@ -433,16 +421,15 @@ DbTable* db_get_table_aux(Process *p,
if (bucket->pu.tb != NULL) {
if (is_atom(bucket->u.name_atom)) { /* single */
- if (bucket->u.name_atom == id) {
- tb = db_ref(bucket->pu.tb, kind);
- }
+ if (bucket->u.name_atom == id)
+ tb = bucket->pu.tb;
}
else { /* multi */
Uint cnt = unsigned_val(bucket->u.mcnt);
Uint i;
for (i=0; i<cnt; i++) {
if (bucket->pu.mvec[i].u.name_atom == id) {
- tb = db_ref(bucket->pu.mvec[i].pu.tb, kind);
+ tb = bucket->pu.mvec[i].pu.tb;
break;
}
}
@@ -450,7 +437,7 @@ DbTable* db_get_table_aux(Process *p,
}
}
if (tb) {
- db_lock_take_over_ref(tb, kind);
+ db_lock(tb, kind);
if (tb->common.id != id
|| ((tb->common.status & what) == 0 && p->id != tb->common.owner)) {
db_unlock(tb, kind);
@@ -624,11 +611,11 @@ done:
*/
static ERTS_INLINE void local_fix_table(DbTable* tb)
{
- erts_refc_inc(&tb->common.fixref, 1);
+ erts_refc_inc(&tb->common.ref, 1);
}
static ERTS_INLINE void local_unfix_table(DbTable* tb)
{
- if (erts_refc_dectest(&tb->common.fixref, 0) == 0) {
+ if (erts_refc_dectest(&tb->common.ref, 0) == 0) {
ASSERT(IS_HASH_TABLE(tb->common.status));
db_unfix_table_hash(&(tb->hash));
}
@@ -1444,6 +1431,7 @@ BIF_RETTYPE ets_new_2(BIF_ALIST_2)
tb->common.type = status & ERTS_ETS_TABLE_TYPES;
/* Note, 'type' is *read only* from now on... */
#endif
+ erts_refc_init(&tb->common.ref, 0);
db_init_lock(tb, status & (DB_FINE_LOCKED|DB_FREQ_READ),
"db_tab", "db_tab_fix");
tb->common.keypos = keypos;
@@ -1466,7 +1454,7 @@ BIF_RETTYPE ets_new_2(BIF_ALIST_2)
"** Too many db tables **\n");
free_heir_data(tb);
tb->common.meth->db_free_table(tb);
- db_unref(tb, LCK_NONE);
+ free_dbtable(tb);
BIF_ERROR(BIF_P, SYSTEM_LIMIT);
}
@@ -1500,9 +1488,10 @@ BIF_RETTYPE ets_new_2(BIF_ALIST_2)
free_slot(slot);
erts_smp_rwmtx_rwunlock(mmtl);
- db_lock_take_over_ref(tb,LCK_WRITE);
+ db_lock(tb,LCK_WRITE);
free_heir_data(tb);
tb->common.meth->db_free_table(tb);
+ schedule_free_dbtable(tb);
db_unlock(tb,LCK_WRITE);
BIF_ERROR(BIF_P, BADARG);
}
@@ -2874,8 +2863,7 @@ void init_db(void)
meta_pid_to_tab->common.meth = &db_hash;
meta_pid_to_tab->common.compress = 0;
- erts_refc_init(&meta_pid_to_tab->common.ref, 1);
- erts_refc_init(&meta_pid_to_tab->common.fixref, 0);
+ erts_refc_init(&meta_pid_to_tab->common.ref, 0);
/* Neither rwlock or fixlock used
db_init_lock(meta_pid_to_tab, "meta_pid_to_tab", "meta_pid_to_tab_FIX");*/
@@ -2907,8 +2895,7 @@ void init_db(void)
meta_pid_to_fixed_tab->common.meth = &db_hash;
meta_pid_to_fixed_tab->common.compress = 0;
- erts_refc_init(&meta_pid_to_fixed_tab->common.ref, 1);
- erts_refc_init(&meta_pid_to_fixed_tab->common.fixref, 0);
+ erts_refc_init(&meta_pid_to_fixed_tab->common.ref, 0);
/* Neither rwlock or fixlock used
db_init_lock(meta_pid_to_fixed_tab, "meta_pid_to_fixed_tab", "meta_pid_to_fixed_tab_FIX");*/
@@ -3066,12 +3053,10 @@ retry:
to_pid, to_locks,
ERTS_P2P_FLG_TRY_LOCK);
if (to_proc == ERTS_PROC_LOCK_BUSY) {
- db_ref(tb, LCK_NONE); /* while unlocked */
db_unlock(tb,LCK_WRITE);
to_proc = erts_pid2proc(p, ERTS_PROC_LOCK_MAIN,
to_pid, to_locks);
db_lock(tb,LCK_WRITE);
- tb = db_unref(tb, LCK_NONE);
ASSERT(tb != NULL);
if (tb->common.owner != p->id) {
@@ -3182,13 +3167,13 @@ erts_db_process_exiting(Process *c_p, ErtsProcLocks c_p_locks)
erts_smp_rwmtx_t *mmtl = get_meta_main_tab_lock(ix);
erts_smp_rwmtx_rlock(mmtl);
if (!IS_SLOT_FREE(ix)) {
- tb = db_ref(GET_ANY_SLOT_TAB(ix), LCK_WRITE);
+ tb = GET_ANY_SLOT_TAB(ix);
ASSERT(tb);
}
erts_smp_rwmtx_runlock(mmtl);
if (tb) {
int do_yield;
- db_lock_take_over_ref(tb, LCK_WRITE);
+ db_lock(tb, LCK_WRITE);
/* Ownership may have changed since
we looked up the table. */
if (tb->common.owner != pid) {
@@ -3270,7 +3255,7 @@ erts_db_process_exiting(Process *c_p, ErtsProcLocks c_p_locks)
erts_smp_rwmtx_t *mmtl = get_meta_main_tab_lock(ix);
erts_smp_rwmtx_rlock(mmtl);
if (IS_SLOT_ALIVE(ix)) {
- tb = db_ref(meta_main_tab[ix].u.tb, LCK_WRITE_REC);
+ tb = meta_main_tab[ix].u.tb;
ASSERT(tb);
}
erts_smp_rwmtx_runlock(mmtl);
@@ -3278,7 +3263,7 @@ erts_db_process_exiting(Process *c_p, ErtsProcLocks c_p_locks)
int reds;
DbFixation** pp;
- db_lock_take_over_ref(tb, LCK_WRITE_REC);
+ db_lock(tb, LCK_WRITE_REC);
#ifdef ERTS_SMP
erts_smp_mtx_lock(&tb->common.fixlock);
#endif
@@ -3289,7 +3274,7 @@ erts_db_process_exiting(Process *c_p, ErtsProcLocks c_p_locks)
if ((*pp)->pid == pid) {
DbFixation* fix = *pp;
long diff = -(long)fix->counter;
- erts_refc_add(&tb->common.fixref,diff,0);
+ erts_refc_add(&tb->common.ref,diff,0);
*pp = fix->next;
erts_db_free(ERTS_ALC_T_DB_FIXATION,
tb, fix, sizeof(DbFixation));
@@ -3364,7 +3349,7 @@ static void fix_table_locked(Process* p, DbTable* tb)
#ifdef ERTS_SMP
erts_smp_mtx_lock(&tb->common.fixlock);
#endif
- erts_refc_inc(&tb->common.fixref,1);
+ erts_refc_inc(&tb->common.ref,1);
fix = tb->common.fixations;
if (fix == NULL) {
get_now(&(tb->common.megasec),
@@ -3418,7 +3403,7 @@ static void unfix_table_locked(Process* p, DbTable* tb,
for (pp = &tb->common.fixations; *pp != NULL; pp = &(*pp)->next) {
if ((*pp)->pid == p->id) {
DbFixation* fix = *pp;
- erts_refc_dec(&tb->common.fixref,0);
+ erts_refc_dec(&tb->common.ref,0);
--(fix->counter);
ASSERT(fix->counter >= 0);
if (fix->counter > 0) {
@@ -3448,7 +3433,6 @@ unlocked:
#ifdef ERTS_SMP
if (*kind_p == LCK_READ && tb->common.is_thread_safe) {
/* Must have write lock while purging pseudo-deleted (OTP-8166) */
- db_ref(tb, LCK_WRITE); /* LCK_WRITE need it, but not LCK_READ */
erts_smp_rwmtx_runlock(&tb->common.rwlock);
erts_smp_rwmtx_rwlock(&tb->common.rwlock);
*kind_p = LCK_WRITE;
@@ -3467,6 +3451,8 @@ static void free_fixations_locked(DbTable *tb)
fix = tb->common.fixations;
while (fix != NULL) {
+ long diff = -(long)fix->counter;
+ erts_refc_add(&tb->common.ref,diff,0);
next_fix = fix->next;
db_meta_lock(meta_pid_to_fixed_tab, LCK_WRITE_REC);
db_erase_bag_exact2(meta_pid_to_fixed_tab,
@@ -3590,10 +3576,6 @@ static int free_table_cont(Process *p,
mmtl = get_meta_main_tab_lock(tb->common.slot);
#ifdef ERTS_SMP
if (erts_smp_rwmtx_tryrwlock(mmtl) == EBUSY) {
- /*
- * We keep our increased refc over this op in order to
- * prevent the table from disapearing.
- */
erts_smp_rwmtx_rwunlock(&tb->common.rwlock);
erts_smp_rwmtx_rwlock(mmtl);
erts_smp_rwmtx_rwlock(&tb->common.rwlock);
@@ -3608,7 +3590,7 @@ static int free_table_cont(Process *p,
make_small(tb->common.slot));
db_meta_unlock(meta_pid_to_tab, LCK_WRITE_REC);
}
- db_unref(tb, LCK_NONE);
+ schedule_free_dbtable(tb);
BUMP_REDS(p, 100);
return 0;
}
diff --git a/erts/emulator/beam/erl_db_util.h b/erts/emulator/beam/erl_db_util.h
index 10ba755e80..58ad39d772 100644
--- a/erts/emulator/beam/erl_db_util.h
+++ b/erts/emulator/beam/erl_db_util.h
@@ -206,8 +206,7 @@ typedef struct db_fixation {
*/
typedef struct db_table_common {
- erts_refc_t ref;
- erts_refc_t fixref; /* fixation counter */
+ erts_refc_t ref; /* fixation counter and delete counter */
#ifdef ERTS_SMP
erts_smp_rwmtx_t rwlock; /* rw lock on table */
erts_smp_mtx_t fixlock; /* Protects fixations,megasec,sec,microsec */
@@ -253,7 +252,7 @@ typedef struct db_table_common {
(DB_BAG | DB_SET | DB_DUPLICATE_BAG)))
#define IS_TREE_TABLE(Status) (!!((Status) & \
DB_ORDERED_SET))
-#define NFIXED(T) (erts_refc_read(&(T)->common.fixref,0))
+#define NFIXED(T) (erts_refc_read(&(T)->common.ref,0))
#define IS_FIXED(T) (NFIXED(T) != 0)
Eterm erts_ets_copy_object(Eterm, Process*);