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Fixed possible deadlock in RWLock

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This commit is contained in:
Alexey Milovidov 2019-09-02 03:12:01 +03:00
parent de2586cd15
commit 2d331fb992
1 changed files with 9 additions and 8 deletions
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17
dbms/src/Common/RWLock.cpp
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@ -110,11 +110,12 @@ RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String &
GroupsContainer::iterator it_group;
ClientsContainer::iterator it_client;
/// This object is placed above unique_lock, because it may lock in destructor.
LockHolder res;
std::unique_lock lock(mutex);
/// Check if the same query is acquiring previously acquired lock
LockHolder existing_holder_ptr;
auto this_thread_id = std::this_thread::get_id();
auto it_thread = thread_to_holder.find(this_thread_id);
@ -123,17 +124,17 @@ RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String &
it_query = query_id_to_holder.find(query_id);
if (it_thread != thread_to_holder.end())
existing_holder_ptr = it_thread->second.lock();
res = it_thread->second.lock();
else if (it_query != query_id_to_holder.end())
existing_holder_ptr = it_query->second.lock();
res = it_query->second.lock();
if (existing_holder_ptr)
if (res)
{
/// XXX: it means we can't upgrade lock from read to write - with proper waiting!
if (type != Read || existing_holder_ptr->it_group->type != Read)
if (type != Read || res->it_group->type != Read)
throw Exception("Attempt to acquire exclusive lock recursively", ErrorCodes::LOGICAL_ERROR);
return existing_holder_ptr;
return res;
}
/** If the query already has any active read lock and tries to acquire another read lock
@ -182,7 +183,7 @@ RWLockImpl::LockHolder RWLockImpl::getLock(RWLockImpl::Type type, const String &
throw;
}
LockHolder res(new LockHolderImpl(shared_from_this(), it_group, it_client));
res.reset(new LockHolderImpl(shared_from_this(), it_group, it_client));
/// Wait a notification until we will be the only in the group.
it_group->cv.wait(lock, [&] () { return it_group == queue.begin(); });