gdb/run-on-main-thread.c

   1 /* Run a function on the main thread
   2    Copyright (C) 2019-2023 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include "defs.h"
  20 #include "run-on-main-thread.h"
  21 #include "ser-event.h"
  22 #if CXX_STD_THREAD
  23 #include <thread>
  24 #include <mutex>
  25 #endif
  26 #include "gdbsupport/event-loop.h"
  27
  28 /* The serial event used when posting runnables.  */
  29
  30 static struct serial_event *runnable_event;
  31
  32 /* Runnables that have been posted.  */
  33
  34 static std::vector<std::function<void ()>> runnables;
  35
  36 #if CXX_STD_THREAD
  37
  38 /* Mutex to hold when handling RUNNABLE_EVENT or RUNNABLES.  */
  39
  40 static std::mutex runnable_mutex;
  41
  42 /* The main thread's thread id.  */
  43
  44 static std::thread::id main_thread_id;
  45
  46 #endif
  47
  48 /* Run all the queued runnables.  */
  49
  50 static void
  51 run_events (int error, gdb_client_data client_data)
  52 {
  53   std::vector<std::function<void ()>> local;
  54
  55   /* Hold the lock while changing the globals, but not while running
  56      the runnables.  */
  57   {
  58 #if CXX_STD_THREAD
  59     std::lock_guard<std::mutex> lock (runnable_mutex);
  60 #endif
  61
  62     /* Clear the event fd.  Do this before flushing the events list,
  63        so that any new event post afterwards is sure to re-awaken the
  64        event loop.  */
  65     serial_event_clear (runnable_event);
  66
  67     /* Move the vector in case running a runnable pushes a new
  68        runnable.  */
  69     local = std::move (runnables);
  70   }
  71
  72   for (auto &item : local)
  73     {
  74       try
  75         {
  76           item ();
  77         }
  78       catch (...)
  79         {
  80           /* Ignore exceptions in the callback.  */
  81         }
  82     }
  83 }
  84
  85 /* See run-on-main-thread.h.  */
  86
  87 void
  88 run_on_main_thread (std::function<void ()> &&func)
  89 {
  90 #if CXX_STD_THREAD
  91   std::lock_guard<std::mutex> lock (runnable_mutex);
  92 #endif
  93   runnables.emplace_back (std::move (func));
  94   serial_event_set (runnable_event);
  95 }
  96
  97 #if CXX_STD_THREAD
  98 static bool main_thread_id_initialized = false;
  99 #endif
 100
 101 /* See run-on-main-thread.h.  */
 102
 103 bool
 104 is_main_thread ()
 105 {
 106 #if CXX_STD_THREAD
 107   /* Initialize main_thread_id on first use of is_main_thread.  */
 108   if (!main_thread_id_initialized)
 109     {
 110       main_thread_id_initialized = true;
 111
 112       main_thread_id = std::this_thread::get_id ();
 113     }
 114
 115   return std::this_thread::get_id () == main_thread_id;
 116 #else
 117   return true;
 118 #endif
 119 }
 120
 121 void _initialize_run_on_main_thread ();
 122 void
 123 _initialize_run_on_main_thread ()
 124 {
 125 #if CXX_STD_THREAD
 126   /* The variable main_thread_id should be initialized when entering main, or
 127      at an earlier use, so it should already be initialized here.  */
 128   gdb_assert (main_thread_id_initialized);
 129
 130   /* Assume that we execute this in the main thread.  */
 131   gdb_assert (is_main_thread ());
 132 #endif
 133   runnable_event = make_serial_event ();
 134   add_file_handler (serial_event_fd (runnable_event), run_events, nullptr,
 135                     "run-on-main-thread");
 136 }