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thread-pool.h revision 1.1 
      1 /* Thread pool
      2 
      3    Copyright (C) 2019-2020 Free Software Foundation, Inc.
      4 
      5    This file is part of GDB.
      6 
      7    This program is free software; you can redistribute it and/or modify
      8    it under the terms of the GNU General Public License as published by
      9    the Free Software Foundation; either version 3 of the License, or
     10    (at your option) any later version.
     11 
     12    This program is distributed in the hope that it will be useful,
     13    but WITHOUT ANY WARRANTY; without even the implied warranty of
     14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     15    GNU General Public License for more details.
     16 
     17    You should have received a copy of the GNU General Public License
     18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
     19 
     20 #ifndef GDBSUPPORT_THREAD_POOL_H
     21 #define GDBSUPPORT_THREAD_POOL_H
     22 
     23 #include <queue>
     24 #include <thread>
     25 #include <vector>
     26 #include <functional>
     27 #include <mutex>
     28 #include <condition_variable>
     29 #include <future>
     30 #include "gdbsupport/gdb_optional.h"
     31 
     32 namespace gdb
     33 {
     34 
     35 /* A thread pool.
     36 
     37    There is a single global thread pool, see g_thread_pool.  Tasks can
     38    be submitted to the thread pool.  They will be processed in worker
     39    threads as time allows.  */
     40 class thread_pool
     41 {
     42 public:
     43   /* The sole global thread pool.  */
     44   static thread_pool *g_thread_pool;
     45 
     46   ~thread_pool ();
     47   DISABLE_COPY_AND_ASSIGN (thread_pool);
     48 
     49   /* Set the thread count of this thread pool.  By default, no threads
     50      are created -- the thread count must be set first.  */
     51   void set_thread_count (size_t num_threads);
     52 
     53   /* Return the number of executing threads.  */
     54   size_t thread_count () const
     55   {
     56     return m_thread_count;
     57   }
     58 
     59   /* Post a task to the thread pool.  A future is returned, which can
     60      be used to wait for the result.  */
     61   std::future<void> post_task (std::function<void ()> func);
     62 
     63 private:
     64 
     65   thread_pool () = default;
     66 
     67   /* The callback for each worker thread.  */
     68   void thread_function ();
     69 
     70   /* The current thread count.  */
     71   size_t m_thread_count = 0;
     72 
     73   /* A convenience typedef for the type of a task.  */
     74   typedef std::packaged_task<void ()> task;
     75 
     76   /* The tasks that have not been processed yet.  An optional is used
     77      to represent a task.  If the optional is empty, then this means
     78      that the receiving thread should terminate.  If the optional is
     79      non-empty, then it is an actual task to evaluate.  */
     80   std::queue<optional<task>> m_tasks;
     81 
     82   /* A condition variable and mutex that are used for communication
     83      between the main thread and the worker threads.  */
     84   std::condition_variable m_tasks_cv;
     85   std::mutex m_tasks_mutex;
     86 };
     87 
     88 }
     89 
     90 #endif /* GDBSUPPORT_THREAD_POOL_H */
     91