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Take care of the case where another thread inserts the same key between unlock()/lock()

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greg7mdp
2023-11-13 09:48:49 -05:00
parent 21f14d7a8e
commit ff7bd78206
2 changed files with 17 additions and 7 deletions
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parallel_hashmap/phmap.h
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+12 -3
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@@ -3805,9 +3805,18 @@ protected:
mutexlock = std::move(typename Lockable::ReadWriteLock(inner));
size_t offset = set._find_key(key, hashval);
if (offset == (size_t)-1) {
mutexlock.switch_to_unique();
offset = set.prepare_insert(hashval);
return std::make_tuple(&inner, offset, true);
if (mutexlock.switch_to_unique()) {
// we did an unlock/lock, and another thread could have inserted the same key, so we need to
// do a find() again.
offset = set._find_key(key, hashval);
if (offset == (size_t)-1) {
offset = set.prepare_insert(hashval);
return std::make_tuple(&inner, offset, true);
}
} else {
offset = set.prepare_insert(hashval);
return std::make_tuple(&inner, offset, true);
}
}
return std::make_tuple(&inner, offset, false);
}