Changeset: f8a34ca7beb1 for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/f8a34ca7beb1
Modified Files:
gdk/gdk_bbp.c
gdk/gdk_utils.c
Branch: default
Log Message:
Fix lost wake-up problem.
A lost wake-up occurs when:
- a thread calls MT_cond_signal() of MT_cond_broadcast() (without lock);
- and another thread is between the test of the condition and the call
to MT_cond_wait();
- and no threads are waiting.
We fix this by calling the broadcast while holding the lock.
An alternative fix would be to use a timeout in the wait, but that
requires calls to gettimeofday.
diffs (76 lines):
diff --git a/gdk/gdk_bbp.c b/gdk/gdk_bbp.c
--- a/gdk/gdk_bbp.c
+++ b/gdk/gdk_bbp.c
@@ -3077,8 +3077,10 @@ decref(bat i, bool logical, bool lock, c
BATdelete(BBP_desc(i));
BBPclear(i);
} else {
+ MT_lock_set(&GDKswapLock(i));
BBP_status_off(i, BBPUNLOADING);
MT_cond_broadcast(&GDKswapCond(i));
+ MT_lock_unset(&GDKswapLock(i));
}
}
return refs;
@@ -3254,9 +3256,12 @@ BBPsave(BAT *b)
if (ret == GDK_SUCCEED) {
ret = BATsave(b);
}
- /* clearing bits can be done without the lock */
+ if (lock)
+ MT_lock_set(&GDKswapLock(bid));
BBP_status_off(bid, BBPSAVING);
MT_cond_broadcast(&GDKswapCond(bid));
+ if (lock)
+ MT_lock_unset(&GDKswapLock(bid));
}
return ret;
}
@@ -3313,8 +3318,10 @@ BBPfree(BAT *b)
BBPuncacheit(bid, false);
}
TRC_DEBUG(BAT_, "turn off unloading %d\n", bid);
+ MT_lock_set(&GDKswapLock(bid));
BBP_status_off(bid, BBPUNLOADING);
MT_cond_broadcast(&GDKswapCond(bid));
+ MT_lock_unset(&GDKswapLock(bid));
BBP_unload_dec();
return ret;
}
@@ -3927,8 +3934,12 @@ BBPsync(int cnt, bat *restrict subcommit
if (lock)
MT_lock_unset(&GDKswapLock(i));
ret = BATsave_iter(b, &bi, size);
+ if (lock)
+ MT_lock_set(&GDKswapLock(i));
BBP_status_off(i, BBPSAVING);
MT_cond_broadcast(&GDKswapCond(i));
+ if (lock)
+ MT_lock_unset(&GDKswapLock(i));
}
bip = &bi;
} else {
@@ -4009,8 +4020,12 @@ BBPsync(int cnt, bat *restrict subcommit
* GDK_SUCCEED) */
for (int idx = 1; idx < cnt; idx++) {
bat i = subcommit ? subcommit[idx] : idx;
+ if (lock)
+ MT_lock_set(&GDKswapLock(i));
BBP_status_off(i, BBPSYNCING);
MT_cond_broadcast(&GDKswapCond(i));
+ if (lock)
+ MT_lock_unset(&GDKswapLock(i));
}
return ret;
diff --git a/gdk/gdk_utils.c b/gdk/gdk_utils.c
--- a/gdk/gdk_utils.c
+++ b/gdk/gdk_utils.c
@@ -1016,6 +1016,7 @@ GDKinit(opt *set, int setlen, bool embed
char name[MT_NAME_LEN];
snprintf(name, sizeof(name), "GDKswapLock%d", i);
MT_lock_init(&GDKbatLock[i].swap, name);
+ snprintf(name, sizeof(name), "GDKswapCond%d", i);
MT_cond_init(&GDKbatLock[i].cond, name);
}
if (mnstr_init() < 0) {
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