fix possible deadlock

src/Interpreters/Context.cpp

@@ -3825,9 +3825,9 @@ void Context::initializeBackgroundExecutorsIfNeeded()
         "MergeMutate",
         /*max_threads_count*/background_pool_size,
         /*max_tasks_count*/background_pool_size * background_merges_mutations_concurrency_ratio,
-        CurrentMetrics::BackgroundMergesAndMutationsPoolTask
+        CurrentMetrics::BackgroundMergesAndMutationsPoolTask,
+        background_merges_mutations_scheduling_policy
     );
-    shared->merge_mutate_executor->updateSchedulingPolicy(background_merges_mutations_scheduling_policy);
     LOG_INFO(shared->log, "Initialized background executor for merges and mutations with num_threads={}, num_tasks={}, scheduling_policy={}",
         background_pool_size, background_pool_size * background_merges_mutations_concurrency_ratio, background_merges_mutations_scheduling_policy);
 

src/Storages/MergeTree/MergeTreeBackgroundExecutor.h

@@ -267,6 +267,18 @@ public:
             pool.scheduleOrThrowOnError([this] { threadFunction(); });
     }
 
+    MergeTreeBackgroundExecutor(
+        String name_,
+        size_t threads_count_,
+        size_t max_tasks_count_,
+        CurrentMetrics::Metric metric_,
+        std::string_view policy)
+        requires requires(Queue queue) { queue.updatePolicy(policy); } // Because we use explicit template instantiation
+        : MergeTreeBackgroundExecutor(name_, threads_count_, max_tasks_count_, metric_)
+    {
+        pending.updatePolicy(policy);
+    }
+
     ~MergeTreeBackgroundExecutor()
     {
         wait();