Branch data     Line data    Source code

       1                 :            : #pragma once
       2                 :            : 
       3                 :            : #include <mutable/catalog/Scheduler.hpp>
       4                 :            : #include <condition_variable>
       5                 :            : #include <list>
       6                 :            : #include <future>
       7                 :            : #include <thread>
       8                 :            : 
       9                 :            : 
      10                 :            : namespace m {
      11                 :            : 
      12                 :            : /** This class implements a Scheduler that executes all incoming `DatabaseCommand`s serially.
      13                 :            :  * This means that there is no concurrent execution.
      14                 :            :  * Therefore, a consistent, serial execution of multiple queries is guaranteed. */
      15                 :            : struct SerialScheduler : Scheduler
      16                 :            : {
      17                 :            :     private:
      18                 :            :     /** A thread-safe query plan queue. */
      19                 :            :     struct CommandQueue
      20                 :            :     {
      21                 :            :         private:
      22                 :            :         std::list<queued_command> command_list_;
      23                 :            :         Transaction *running_transaction_; ///< the currently running transaction. Only commands by this transaction are returned.
      24                 :            :         std::mutex mutex_;
      25                 :            :         std::condition_variable has_element_;
      26                 :          1 :         bool closed_ = false;
      27                 :            : 
      28                 :            :         public:
      29                 :          2 :         CommandQueue() = default;
      30                 :          1 :         ~CommandQueue() = default;
      31                 :            : 
      32                 :            :         ///> returns the next queued `ast::Command`. Returns `std::nullopt` if the queue is closed.
      33                 :            :         std::optional<queued_command> pop();
      34                 :            :         /** Inserts the command into the queue. Internally the position in the `command_list_` is determined by the
      35                 :            :          * start time of `Transaction t`. A smaller start time is inserted before a larger start time and elements
      36                 :            :          * with the same start time are ordered in FIFO order by the time of arrival. */
      37                 :            :         void push(Transaction &t, std::unique_ptr<ast::Command> command, Diagnostic &diag, std::promise<bool> promise);
      38                 :            :         void close();    ///< empties and closes the queue without executing the remaining `ast::Command`s.
      39                 :            :         bool is_closed();  ///< signals waiting threads that no more elements will be pushed
      40                 :            :         void stop_transaction(Transaction &t); ///< Marks `t` as no longer running.
      41                 :            :     };
      42                 :            : 
      43                 :            :     static CommandQueue query_queue_; ///< instance of our thread-safe query queue that stores all incoming plans.
      44                 :            :     std::thread schedule_thread_; ///< the worker thread that executes all incoming queries.
      45                 :            : 
      46                 :            :     static std::atomic<int64_t> next_start_time; ///< stores the next transaction start time
      47                 :            : 
      48                 :            :     public:
      49                 :          1 :     SerialScheduler() = default;
      50                 :            :     ~SerialScheduler();
      51                 :            : 
      52                 :            :     std::future<bool> schedule_command(Transaction &t, std::unique_ptr<ast::Command> command, Diagnostic &diag) override;
      53                 :            : 
      54                 :            :     std::unique_ptr<Transaction> begin_transaction() override;
      55                 :            : 
      56                 :            :     bool commit(std::unique_ptr<Transaction> t) override;
      57                 :            : 
      58                 :            :     bool abort(std::unique_ptr<Transaction> t) override;
      59                 :            : 
      60                 :            :     private:
      61                 :            :     /** The method run by the worker thread `schedule_thread_`.
      62                 :            :      * While stopping, the query that is already being executed will complete its execution
      63                 :            :      * but queued queries will not be executed. */
      64                 :            :     static void schedule_thread();
      65                 :            : };
      66                 :            : 
      67                 :            : }