gdbsupport/thread-pool.h

   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 */