Owning future

src/Common/RingBuffer.h

@@ -54,19 +54,24 @@ public:
 
     /// In case of T = std::shared_ptr<Something> it won't cause any allocations
     template <typename Predicate>
-    void eraseAll(Predicate && predicate)
+    bool eraseAll(Predicate && predicate)
     {
         /// Shift all elements to the beginning of the buffer
         std::rotate(buffer.begin(), buffer.begin() + position, buffer.end());
+        position = 0;
+
         /// Remove elements
         auto end_removed = std::remove_if(buffer.begin(), buffer.begin() + count, predicate);
 
+        if (end_removed == buffer.begin() + count)
+            return false;
+
         size_t new_count = std::distance(buffer.begin(), end_removed);
         for (size_t i = new_count; i < count; ++i)
             buffer[i] = T{};
 
         count = new_count;
-        position = 0;
+        return true;
     }
 
     template <class Predicate>

src/Storages/MergeTree/MergeMutateExecutor.cpp

@@ -26,7 +26,7 @@ void MergeTreeBackgroundExecutor::removeTasksCorrespondingToStorage(StorageID id
 {
     std::lock_guard remove_lock(remove_mutex);
 
-    std::vector<ItemPtr> tasks_to_wait;
+    std::vector<ActiveMeta> tasks_to_wait;
     {
         std::lock_guard lock(mutex);
 
@@ -35,23 +35,91 @@ void MergeTreeBackgroundExecutor::removeTasksCorrespondingToStorage(StorageID id
 
         /// Erase storage related tasks from pending and select active tasks to wait for
         pending.eraseAll([&] (auto item) -> bool { return item->task->getStorageID() == id; });
-        tasks_to_wait = active.getAll([&] (auto item) -> bool { return item->task->getStorageID() == id; });
+        tasks_to_wait = active.getAll([&] (auto elem) -> bool { return elem.item->task->getStorageID() == id; });
     }
 
 
-    for (const auto & item : tasks_to_wait)
+    for (auto & [item, future] : tasks_to_wait)
     {
-        assert(item->future.valid());
-        item->future.wait();
+        assert(future.valid());
+        try
+        {
+            future.wait();
+        }
+        catch (...) {}
     }
 
     {
         std::lock_guard lock(mutex);
+
+        for (auto & [item, future] : tasks_to_wait)
+        {
+            assert(item.use_count() == 1);
+            item.reset();
+        }
+
+
         currently_deleting.erase(id);
     }
 }
 
 
+void MergeTreeBackgroundExecutor::routine(ItemPtr item)
+{
+    setThreadName(name.c_str());
+
+    bool checked{false};
+
+    auto check_if_currently_deleting = [&] ()
+    {
+        checked = true;
+        return active.eraseAll([&] (auto & x) { return x.item == item; });
+    };
+
+
+    SCOPE_EXIT({
+        if (checked)
+            return;
+        std::lock_guard guard(mutex);
+        check_if_currently_deleting();
+    });
+
+    try
+    {
+        if (item->task->execute())
+        {
+            std::lock_guard guard(mutex);
+
+            if (check_if_currently_deleting())
+                return;
+
+            pending.tryPush(item);
+            has_tasks.notify_one();
+            return;
+        }
+
+        /// In a situation of a lack of memory this method can throw an exception,
+        /// because it may interact somehow with BackgroundSchedulePool, which may allocate memory
+        /// But it is rather safe, because we have try...catch block here, and another one in ThreadPool.
+        item->task->onCompleted();
+
+        std::lock_guard guard(mutex);
+        has_tasks.notify_one();
+    }
+    catch(...)
+    {
+        std::lock_guard guard(mutex);
+        has_tasks.notify_one();
+        try
+        {
+            item->task->onCompleted();
+        }
+        catch (...) {}
+        tryLogCurrentException(__PRETTY_FUNCTION__);
+    }
+}
+
+
 void MergeTreeBackgroundExecutor::schedulerThreadFunction()
 {
     DENY_ALLOCATIONS_IN_SCOPE;
@@ -71,88 +139,20 @@ void MergeTreeBackgroundExecutor::schedulerThreadFunction()
         if (!pending.tryPop(&item))
             continue;
 
-        status = active.tryPush(item);
-        assert(status);
-
-
-        bool res = pool.trySchedule([this, item] ()
-        {
-            setThreadName(name.c_str());
-
-            /// Storage may want to destroy and it needs to finish all task related to it.
-            /// But checking causes some interaction with storage methods, for example it calls getStorageID.
-            /// So, we must execute this checking once, signal another thread that we are finished and be destroyed.
-            /// Not doing any complex stuff, especially interaction with Storage...
-            /// Calling this check twice may cause segfault.
-            auto check_if_currently_deleting = [&] () -> bool
-            {
-                active.eraseAll([&] (auto x) { return x == item; });
-
-                for (const auto & id : currently_deleting)
-                {
-                    if (item->task->getStorageID() == id)
-                    {
-                        item->promise.set_value();
-                        return true;
-                    }
-                }
-
-                return false;
-            };
-
-            bool checked{false};
-
-            SCOPE_EXIT({
-                if (checked)
-                    return;
-                checked = true;
-                std::lock_guard guard(mutex);
-                check_if_currently_deleting();
-            });
-
-            try
-            {
-                if (item->task->execute())
-                {
-                    std::lock_guard guard(mutex);
-
-                    if (check_if_currently_deleting())
-                        return;
-
-                    pending.tryPush(item);
-                    has_tasks.notify_one();
-                    return;
-                }
-
-                /// In a situation of a lack of memory this method can throw an exception,
-                /// because it may interact somehow with BackgroundSchedulePool, which may allocate memory
-                /// But it is rather safe, because we have try...catch block here, and another one in ThreadPool.
-                item->task->onCompleted();
-
-                std::lock_guard guard(mutex);
-                has_tasks.notify_one();
-            }
-            catch(...)
-            {
-                std::lock_guard guard(mutex);
-                has_tasks.notify_one();
-                try
-                {
-                    item->task->onCompleted();
-                }
-                catch (...) {}
-                tryLogCurrentException(__PRETTY_FUNCTION__);
-            }
-
-        });
+        auto thread_pool_job = std::make_shared<std::packaged_task<void()>>([this, item] { routine(item); });
+        auto future = thread_pool_job->get_future();
+        bool res = pool.trySchedule([thread_pool_job] { (*thread_pool_job)(); });
 
         if (!res)
         {
-            active.eraseAll([&] (auto x) { return x == item; });
+            active.eraseAll([&] (auto x) { return x.item == item; });
             status = pending.tryPush(item);
             assert(status);
+            continue;
         }
 
+        status = active.tryPush({std::move(item), std::move(future)});
+        assert(status);
     }
 }
 

src/Storages/MergeTree/MergeMutateExecutor.h

@@ -136,8 +136,6 @@ private:
         max_tasks_count = new_max_tasks_count;
     }
 
-    void schedulerThreadFunction();
-
     static String toString(Type type);
 
     Type type;
@@ -156,22 +154,28 @@ private:
         explicit Item(ExecutableTaskPtr && task_, CurrentMetrics::Metric metric_)
             : task(std::move(task_))
             , increment(std::move(metric_))
-            , future(promise.get_future())
         {
         }
 
         ExecutableTaskPtr task;
         CurrentMetrics::Increment increment;
-
-        std::promise<void> promise;
-        std::future<void> future;
     };
 
     using ItemPtr = std::shared_ptr<Item>;
 
+    void routine(ItemPtr item);
+    void schedulerThreadFunction();
+
     /// Initially it will be empty
     RingBuffer<ItemPtr> pending{0};
-    RingBuffer<ItemPtr> active{0};
+
+    struct ActiveMeta
+    {
+        ItemPtr item;
+        std::shared_future<void> future;
+    };
+
+    RingBuffer<ActiveMeta> active{0};
     std::set<StorageID> currently_deleting;
 
     std::mutex remove_mutex;