Revert "Fix RWLock inconsistency after write lock timeout"

src/Common/RWLock.cpp

@@ -3,8 +3,6 @@
 #include <Common/Exception.h>
 #include <Common/CurrentMetrics.h>
 #include <Common/ProfileEvents.h>
-#include <IO/Operators.h>
-#include <IO/WriteBufferFromString.h>
 
 
 namespace ProfileEvents
@@ -157,34 +155,25 @@ RWLockImpl::getLock(RWLockImpl::Type type, const String & query_id, const std::c
 
     if (type == Type::Write)
     {
-        /// Always add a group for a writer (writes are never performed simultaneously).
         writers_queue.emplace_back(type);  /// SM1: may throw (nothing to roll back)
     }
-    else
+    else if (readers_queue.empty() ||
+            (rdlock_owner == readers_queue.begin() && readers_queue.size() == 1 && !writers_queue.empty()))
     {
-        /// We don't always add a group to readers_queue here because multiple readers can use the same group.
-        /// We can reuse the last group if the last group didn't get ownership yet,
-        /// or even if it got ownership but there are no writers waiting in writers_queue.
-        bool can_use_last_group = !readers_queue.empty() && (!readers_queue.back().ownership || writers_queue.empty());
-
-        if (!can_use_last_group)
         readers_queue.emplace_back(type);  /// SM1: may throw (nothing to roll back)
     }
-
     GroupsContainer::iterator it_group =
             (type == Type::Write) ? std::prev(writers_queue.end()) : std::prev(readers_queue.end());
 
     /// Lock is free to acquire
     if (rdlock_owner == readers_queue.end() && wrlock_owner == writers_queue.end())
     {
-        /// Set `rdlock_owner` or `wrlock_owner` and make it owner.
         (type == Read ? rdlock_owner : wrlock_owner) = it_group;  /// SM2: nothrow
-        grantOwnership(it_group);
     }
     else
     {
         /// Wait until our group becomes the lock owner
-        const auto predicate = [&] () { return it_group->ownership; };
+        const auto predicate = [&] () { return it_group == (type == Read ? rdlock_owner : wrlock_owner); };
 
         if (lock_deadline_tp == std::chrono::time_point<std::chrono::steady_clock>::max())
         {
@@ -204,20 +193,15 @@ RWLockImpl::getLock(RWLockImpl::Type type, const String & query_id, const std::c
                 /// Rollback(SM1): nothrow
                 if (it_group->requests == 0)
                 {
-                    ((type == Read) ? readers_queue : writers_queue).erase(it_group);
+                    /// When WRITE lock fails, we need to notify next read that is waiting,
+                    /// to avoid handing request, hence next=true.
+                    dropOwnerGroupAndPassOwnership(it_group, /* next= */ true);
                 }
-                /// While we were waiting for this write lock (which has just failed) more readers could start waiting,
-                /// we need to wake up them now.
-                if ((rdlock_owner != readers_queue.end()) && writers_queue.empty())
-                    grantOwnershipToAllReaders();
                 return nullptr;
             }
         }
     }
 
-    /// Our group must be an owner here.
-    chassert(it_group->ownership);
-
     if (request_has_query_id)
     {
         try
@@ -232,7 +216,7 @@ RWLockImpl::getLock(RWLockImpl::Type type, const String & query_id, const std::c
             /// Methods std::list<>::emplace_back() and std::unordered_map<>::emplace() provide strong exception safety
             /// We only need to roll back the changes to these objects: owner_queries and the readers/writers queue
             if (it_group->requests == 0)
-                dropOwnerGroupAndPassOwnership(it_group);  /// Rollback(SM1): nothrow
+                dropOwnerGroupAndPassOwnership(it_group, /* next= */ false);  /// Rollback(SM1): nothrow
 
             throw;
         }
@@ -253,28 +237,19 @@ RWLockImpl::getLock(RWLockImpl::Type type, const String & query_id, const std::c
   * it is guaranteed that all three steps have been executed successfully and the resulting state is consistent.
   * With the mutex locked the order of steps to restore the lock's state can be arbitrary
   *
-  * We do not employ try-catch: if something bad happens and chassert() is disabled, there is nothing we can do
+  * We do not employ try-catch: if something bad happens, there is nothing we can do =(
-  * (we can't throw an exception here because RWLockImpl::unlock() is called from the destructor ~LockHolderImpl).
   */
 void RWLockImpl::unlock(GroupsContainer::iterator group_it, const String & query_id) noexcept
 {
     std::lock_guard state_lock(internal_state_mtx);
 
-    /// Our group must be an owner here.
+    /// All of these are Undefined behavior and nothing we can do!
-    if (!group_it->ownership)
+    if (rdlock_owner == readers_queue.end() && wrlock_owner == writers_queue.end())
-    {
-        chassert(false && "RWLockImpl::unlock() is called for a non-owner group");
         return;
-    }
+    if (rdlock_owner != readers_queue.end() && group_it != rdlock_owner)
-
+        return;
-    /// Check consistency.
+    if (wrlock_owner != writers_queue.end() && group_it != wrlock_owner)
-    if ((group_it->type == Read)
-            ? !(rdlock_owner != readers_queue.end() && wrlock_owner == writers_queue.end())
-            : !(wrlock_owner != writers_queue.end() && rdlock_owner == readers_queue.end() && group_it == wrlock_owner))
-    {
-        chassert(false && "RWLockImpl::unlock() found the rwlock inconsistent");
         return;
-    }
 
     /// If query_id is not empty it must be listed in parent->owner_queries
     if (query_id != NO_QUERY)
@@ -289,26 +264,12 @@ void RWLockImpl::unlock(GroupsContainer::iterator group_it, const String & query
 
     /// If we are the last remaining referrer, remove this QNode and notify the next one
     if (--group_it->requests == 0)               /// SM: nothrow
-        dropOwnerGroupAndPassOwnership(group_it);
+        dropOwnerGroupAndPassOwnership(group_it, /* next= */ false);
 }
 
 
-void RWLockImpl::dropOwnerGroupAndPassOwnership(GroupsContainer::iterator group_it) noexcept
+void RWLockImpl::dropOwnerGroupAndPassOwnership(GroupsContainer::iterator group_it, bool next) noexcept
 {
-    /// All readers with ownership must finish before switching to write phase.
-    /// Such readers has iterators from `readers_queue.begin()` to `rdlock_owner`, so if `rdlock_owner` is equal to `readers_queue.begin()`
-    /// that means there is only one reader with ownership left in the readers_queue and we can proceed to generic procedure.
-    if ((group_it->type == Read) && (rdlock_owner != readers_queue.begin()) && (rdlock_owner != readers_queue.end()))
-    {
-        if (rdlock_owner == group_it)
-            --rdlock_owner;
-        readers_queue.erase(group_it);
-        /// If there are no writers waiting in writers_queue then we can wake up other readers.
-        if (writers_queue.empty())
-            grantOwnershipToAllReaders();
-        return;
-    }
-
     rdlock_owner = readers_queue.end();
     wrlock_owner = writers_queue.end();
 
@@ -317,86 +278,42 @@ void RWLockImpl::dropOwnerGroupAndPassOwnership(GroupsContainer::iterator group_
         readers_queue.erase(group_it);
         /// Prepare next phase
         if (!writers_queue.empty())
+        {
             wrlock_owner = writers_queue.begin();
+        }
         else
+        {
             rdlock_owner = readers_queue.begin();
         }
+    }
     else
     {
         writers_queue.erase(group_it);
         /// Prepare next phase
         if (!readers_queue.empty())
-            rdlock_owner = readers_queue.begin();
+        {
+            if (next && readers_queue.size() > 1)
+            {
+                rdlock_owner = std::next(readers_queue.begin());
+            }
             else
+            {
+                rdlock_owner = readers_queue.begin();
+            }
+        }
+        else
+        {
             wrlock_owner = writers_queue.begin();
         }
+    }
 
     if (rdlock_owner != readers_queue.end())
     {
-        grantOwnershipToAllReaders();
+        rdlock_owner->cv.notify_all();
     }
     else if (wrlock_owner != writers_queue.end())
     {
-        grantOwnership(wrlock_owner);
+        wrlock_owner->cv.notify_one();
     }
 }
-
-
-void RWLockImpl::grantOwnership(GroupsContainer::iterator group_it) noexcept
-{
-    if (!group_it->ownership)
-    {
-        group_it->ownership = true;
-        group_it->cv.notify_all();
-    }
-}
-
-
-void RWLockImpl::grantOwnershipToAllReaders() noexcept
-{
-    if (rdlock_owner != readers_queue.end())
-    {
-        size_t num_new_owners = 0;
-
-        for (;;)
-        {
-            if (!rdlock_owner->ownership)
-                ++num_new_owners;
-            grantOwnership(rdlock_owner);
-            if (std::next(rdlock_owner) == readers_queue.end())
-                break;
-            ++rdlock_owner;
-        }
-
-        /// There couldn't be more than one reader group which is not an owner.
-        /// (Because we add a new reader group only if the last reader group is already an owner - see the `can_use_last_group` variable.)
-        chassert(num_new_owners <= 1);
-    }
-}
-
-
-std::unordered_map<String, size_t> RWLockImpl::getOwnerQueryIds() const
-{
-    std::lock_guard lock{internal_state_mtx};
-    return owner_queries;
-}
-
-
-String RWLockImpl::getOwnerQueryIdsDescription() const
-{
-    auto map = getOwnerQueryIds();
-    WriteBufferFromOwnString out;
-    bool need_comma = false;
-    for (const auto & [query_id, num_owners] : map)
-    {
-        if (need_comma)
-            out << ", ";
-        out << query_id;
-        if (num_owners != 1)
-            out << " (" << num_owners << ")";
-        need_comma = true;
-    }
-    return out.str();
-}
-
 }

src/Common/RWLock.h

@@ -62,42 +62,35 @@ public:
     inline static const String NO_QUERY = String();
     inline static const auto default_locking_timeout_ms = std::chrono::milliseconds(120000);
 
-    /// Returns all query_id owning locks (both read and write) right now.
-    /// !! This function are for debugging and logging purposes only, DO NOT use them for synchronization!
-    std::unordered_map<String, size_t> getOwnerQueryIds() const;
-    String getOwnerQueryIdsDescription() const;
-
 private:
     /// Group of locking requests that should be granted simultaneously
     /// i.e. one or several readers or a single writer
     struct Group
     {
         const Type type;
-        size_t requests = 0;
+        size_t requests;
 
-        bool ownership = false; /// whether this group got ownership? (that means `cv` is notified and the locking requests should stop waiting)
         std::condition_variable cv; /// all locking requests of the group wait on this condvar
 
-        explicit Group(Type type_) : type{type_} {}
+        explicit Group(Type type_) : type{type_}, requests{0} {}
     };
 
     using GroupsContainer = std::list<Group>;
-    using OwnerQueryIds = std::unordered_map<String /* query_id */, size_t /* num_owners */>;
+    using OwnerQueryIds = std::unordered_map<String, size_t>;
 
     mutable std::mutex internal_state_mtx;
 
     GroupsContainer readers_queue;
     GroupsContainer writers_queue;
-    GroupsContainer::iterator rdlock_owner{readers_queue.end()};  /// last group with ownership in readers_queue in read phase
+    GroupsContainer::iterator rdlock_owner{readers_queue.end()};  /// equals to readers_queue.begin() in read phase
-                                                                  /// or readers_queue.end() in writer phase
+                                                                  /// or readers_queue.end() otherwise
     GroupsContainer::iterator wrlock_owner{writers_queue.end()};  /// equals to writers_queue.begin() in write phase
-                                                                  /// or writers_queue.end() in read phase
+                                                                  /// or writers_queue.end() otherwise
     OwnerQueryIds owner_queries;
 
     RWLockImpl() = default;
     void unlock(GroupsContainer::iterator group_it, const String & query_id) noexcept;
-    void dropOwnerGroupAndPassOwnership(GroupsContainer::iterator group_it) noexcept;
+    /// @param next - notify next after begin, used on writer lock failures
-    void grantOwnership(GroupsContainer::iterator group_it) noexcept;
+    void dropOwnerGroupAndPassOwnership(GroupsContainer::iterator group_it, bool next) noexcept;
-    void grantOwnershipToAllReaders() noexcept;
 };
 }

src/Common/tests/gtest_rw_lock.cpp

@@ -24,39 +24,6 @@ namespace DB
 }
 
 
-namespace
-{
-    class Events
-    {
-    public:
-        Events() : start_time(std::chrono::steady_clock::now()) {}
-
-        void add(String && event)
-        {
-            String timepoint = std::to_string(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - start_time).count());
-            if (timepoint.length() < 5)
-                timepoint.insert(0, 5 - timepoint.length(), ' ');
-            std::lock_guard lock{mutex};
-            //std::cout << timepoint << " : " << event << std::endl;
-            events.emplace_back(std::move(event));
-        }
-
-        void check(const Strings & expected_events)
-        {
-            std::lock_guard lock{mutex};
-            EXPECT_EQ(events.size(), expected_events.size());
-            for (size_t i = 0; i != events.size(); ++i)
-                EXPECT_EQ(events[i], (i < expected_events.size() ? expected_events[i] : ""));
-        }
-
-    private:
-        const std::chrono::time_point<std::chrono::steady_clock> start_time;
-        Strings events TSA_GUARDED_BY(mutex);
-        mutable std::mutex mutex;
-    };
-}
-
-
 TEST(Common, RWLock1)
 {
     /// Tests with threads require this, because otherwise
@@ -320,200 +287,3 @@ TEST(Common, RWLockNotUpgradeableWithNoQuery)
 
     read_thread.join();
 }
-
-
-TEST(Common, RWLockWriteLockTimeoutDuringRead)
-{
-    static auto rw_lock = RWLockImpl::create();
-    Events events;
-
-    std::thread ra_thread([&] ()
-    {
-        events.add("Locking ra");
-        auto ra = rw_lock->getLock(RWLockImpl::Read, "ra");
-        events.add(ra ? "Locked ra" : "Failed to lock ra");
-        EXPECT_NE(ra, nullptr);
-
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(400));
-
-        events.add("Unlocking ra");
-        ra.reset();
-        events.add("Unlocked ra");
-    });
-
-    std::thread wc_thread([&] ()
-    {
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(100));
-        events.add("Locking wc");
-        auto wc = rw_lock->getLock(RWLockImpl::Write, "wc", std::chrono::milliseconds(200));
-        events.add(wc ? "Locked wc" : "Failed to lock wc");
-        EXPECT_EQ(wc, nullptr);
-    });
-
-    ra_thread.join();
-    wc_thread.join();
-
-    {
-        events.add("Locking wd");
-        auto wd = rw_lock->getLock(RWLockImpl::Write, "wd", std::chrono::milliseconds(1000));
-        events.add(wd ? "Locked wd" : "Failed to lock wd");
-        EXPECT_NE(wd, nullptr);
-        events.add("Unlocking wd");
-        wd.reset();
-        events.add("Unlocked wd");
-    }
-
-    events.check(
-        {"Locking ra",
-         "Locked ra",
-         "Locking wc",
-         "Failed to lock wc",
-         "Unlocking ra",
-         "Unlocked ra",
-         "Locking wd",
-         "Locked wd",
-         "Unlocking wd",
-         "Unlocked wd"});
-}
-
-
-TEST(Common, RWLockWriteLockTimeoutDuringTwoReads)
-{
-    static auto rw_lock = RWLockImpl::create();
-    Events events;
-
-    std::thread ra_thread([&] ()
-    {
-        events.add("Locking ra");
-        auto ra = rw_lock->getLock(RWLockImpl::Read, "ra");
-        events.add(ra ? "Locked ra" : "Failed to lock ra");
-        EXPECT_NE(ra, nullptr);
-
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(400));
-
-        events.add("Unlocking ra");
-        ra.reset();
-        events.add("Unlocked ra");
-    });
-
-    std::thread rb_thread([&] ()
-    {
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(200));
-        events.add("Locking rb");
-
-        auto rb = rw_lock->getLock(RWLockImpl::Read, "rb");
-        events.add(rb ? "Locked rb" : "Failed to lock rb");
-        EXPECT_NE(rb, nullptr);
-
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(200));
-        events.add("Unlocking rb");
-        rb.reset();
-        events.add("Unlocked rb");
-    });
-
-    std::thread wc_thread([&] ()
-    {
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(100));
-        events.add("Locking wc");
-        auto wc = rw_lock->getLock(RWLockImpl::Write, "wc", std::chrono::milliseconds(200));
-        events.add(wc ? "Locked wc" : "Failed to lock wc");
-        EXPECT_EQ(wc, nullptr);
-    });
-
-    ra_thread.join();
-    rb_thread.join();
-    wc_thread.join();
-
-    {
-        events.add("Locking wd");
-        auto wd = rw_lock->getLock(RWLockImpl::Write, "wd", std::chrono::milliseconds(1000));
-        events.add(wd ? "Locked wd" : "Failed to lock wd");
-        EXPECT_NE(wd, nullptr);
-        events.add("Unlocking wd");
-        wd.reset();
-        events.add("Unlocked wd");
-    }
-
-    events.check(
-        {"Locking ra",
-         "Locked ra",
-         "Locking wc",
-         "Locking rb",
-         "Failed to lock wc",
-         "Locked rb",
-         "Unlocking ra",
-         "Unlocked ra",
-         "Unlocking rb",
-         "Unlocked rb",
-         "Locking wd",
-         "Locked wd",
-         "Unlocking wd",
-         "Unlocked wd"});
-}
-
-
-TEST(Common, RWLockWriteLockTimeoutDuringWriteWithWaitingRead)
-{
-    static auto rw_lock = RWLockImpl::create();
-    Events events;
-
-    std::thread wa_thread([&] ()
-    {
-        events.add("Locking wa");
-        auto wa = rw_lock->getLock(RWLockImpl::Write, "wa");
-        events.add(wa ? "Locked wa" : "Failed to lock wa");
-        EXPECT_NE(wa, nullptr);
-
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(500));
-
-        events.add("Unlocking wa");
-        wa.reset();
-        events.add("Unlocked wa");
-    });
-
-    std::thread wb_thread([&] ()
-    {
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(100));
-        events.add("Locking wb");
-        auto wc = rw_lock->getLock(RWLockImpl::Write, "wc", std::chrono::milliseconds(200));
-        events.add(wc ? "Locked wb" : "Failed to lock wb");
-        EXPECT_EQ(wc, nullptr);
-    });
-    
-    std::thread rc_thread([&] ()
-    {
-        std::this_thread::sleep_for(std::chrono::duration<int, std::milli>(200));
-        events.add("Locking rc");
-        auto rc = rw_lock->getLock(RWLockImpl::Read, "rc", std::chrono::milliseconds(200));
-        events.add(rc ? "Locked rc" : "Failed to lock rc");
-        EXPECT_EQ(rc, nullptr);
-    });
-
-    wa_thread.join();
-    wb_thread.join();
-    rc_thread.join();
-
-    {
-        events.add("Locking wd");
-        auto wd = rw_lock->getLock(RWLockImpl::Write, "wd", std::chrono::milliseconds(1000));
-        events.add(wd ? "Locked wd" : "Failed to lock wd");
-        EXPECT_NE(wd, nullptr);
-        events.add("Unlocking wd");
-        wd.reset();
-        events.add("Unlocked wd");
-    }
-
-    events.check(
-        {"Locking wa",
-         "Locked wa",
-         "Locking wb",
-         "Locking rc",
-         "Failed to lock wb",
-         "Failed to lock rc",
-         "Unlocking wa",
-         "Unlocked wa",
-         "Locking wd",
-         "Locked wd",
-         "Unlocking wd",
-         "Unlocked wd"});
-}

src/Storages/IStorage.cpp

@@ -41,8 +41,8 @@ RWLockImpl::LockHolder IStorage::tryLockTimed(
     {
         const String type_str = type == RWLockImpl::Type::Read ? "READ" : "WRITE";
         throw Exception(ErrorCodes::DEADLOCK_AVOIDED,
-            "{} locking attempt on \"{}\" has timed out! ({}ms) Possible deadlock avoided. Client should retry. Owner query ids: {}",
+            "{} locking attempt on \"{}\" has timed out! ({}ms) Possible deadlock avoided. Client should retry",
-            type_str, getStorageID(), acquire_timeout.count(), rwlock->getOwnerQueryIdsDescription());
+            type_str, getStorageID(), acquire_timeout.count());
     }
     return lock_holder;
 }

tests/integration/test_backup_restore_on_cluster/test_concurrency.py

@@ -216,7 +216,7 @@ def test_create_or_drop_tables_during_backup(db_engine, table_engine):
             node = nodes[randint(0, num_nodes - 1)]
             # "DROP TABLE IF EXISTS" still can throw some errors (e.g. "WRITE locking attempt on node0 has timed out!")
             # So we use query_and_get_answer_with_error() to ignore any errors.
-            # `lock_acquire_timeout` is reduced because we don't wait our test to wait too long.
+            # `lock_acquire_timeout` is also reduced because we don't wait our test to wait too long.
             node.query_and_get_answer_with_error(
                 f"DROP TABLE IF EXISTS {table_name} SYNC",
                 settings={"lock_acquire_timeout": 10},
@@ -227,24 +227,15 @@ def test_create_or_drop_tables_during_backup(db_engine, table_engine):
             table_name1 = f"mydb.tbl{randint(1, num_nodes)}"
             table_name2 = f"mydb.tbl{randint(1, num_nodes)}"
             node = nodes[randint(0, num_nodes - 1)]
-            # `lock_acquire_timeout` is reduced because we don't wait our test to wait too long.
             node.query_and_get_answer_with_error(
-                f"RENAME TABLE {table_name1} TO {table_name2}",
+                f"RENAME TABLE {table_name1} TO {table_name2}"
-                settings={"lock_acquire_timeout": 10},
             )
 
     def truncate_tables():
         while time.time() < end_time:
             table_name = f"mydb.tbl{randint(1, num_nodes)}"
             node = nodes[randint(0, num_nodes - 1)]
-            # "TRUNCATE TABLE IF EXISTS" still can throw some errors
+            node.query(f"TRUNCATE TABLE IF EXISTS {table_name} SYNC")
-            # (e.g. "WRITE locking attempt on node0 has timed out!" if the table engine is "Log").
-            # So we use query_and_get_answer_with_error() to ignore any errors.
-            # `lock_acquire_timeout` is reduced because we don't wait our test to wait too long.
-            node.query_and_get_answer_with_error(
-                f"TRUNCATE TABLE IF EXISTS {table_name} SYNC",
-                settings={"lock_acquire_timeout": 10},
-            )
 
     def make_backups():
         ids = []