gdb/run-on-main-thread.c

   1 /* Run a function on the main thread
   2    Copyright (C) 2019-2024 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 "run-on-main-thread.h"
  20 #include "ser-event.h"
  21 #if CXX_STD_THREAD
  22 #include <thread>
  23 #include <mutex>
  24 #endif
  25 #include "gdbsupport/event-loop.h"
  26
  27 /* The serial event used when posting runnables.  */
  28
  29 static struct serial_event *runnable_event;
  30
  31 /* Runnables that have been posted.  */
  32
  33 static std::vector<std::function<void ()>> runnables;
  34
  35 #if CXX_STD_THREAD
  36
  37 /* Mutex to hold when handling RUNNABLE_EVENT or RUNNABLES.  */
  38
  39 static std::mutex runnable_mutex;
  40
  41 /* The main thread's thread id.  */
  42
  43 static std::thread::id main_thread_id;
  44
  45 #endif
  46
  47 /* Run all the queued runnables.  */
  48
  49 static void
  50 run_events (int error, gdb_client_data client_data)
  51 {
  52   std::vector<std::function<void ()>> local;
  53
  54   /* Hold the lock while changing the globals, but not while running
  55      the runnables.  */
  56   {
  57 #if CXX_STD_THREAD
  58     std::lock_guard<std::mutex> lock (runnable_mutex);
  59 #endif
  60
  61     /* Clear the event fd.  Do this before flushing the events list,
  62        so that any new event post afterwards is sure to re-awaken the
  63        event loop.  */
  64     serial_event_clear (runnable_event);
  65
  66     /* Move the vector in case running a runnable pushes a new
  67        runnable.  */
  68     local = std::move (runnables);
  69   }
  70
  71   for (auto &item : local)
  72     {
  73       try
  74         {
  75           item ();
  76         }
  77       catch (...)
  78         {
  79           /* Ignore exceptions in the callback.  */
  80         }
  81     }
  82 }
  83
  84 /* See run-on-main-thread.h.  */
  85
  86 void
  87 run_on_main_thread (std::function<void ()> &&func)
  88 {
  89 #if CXX_STD_THREAD
  90   std::lock_guard<std::mutex> lock (runnable_mutex);
  91 #endif
  92   runnables.emplace_back (std::move (func));
  93   serial_event_set (runnable_event);
  94 }
  95
  96 #if CXX_STD_THREAD
  97 static bool main_thread_id_initialized = false;
  98 #endif
  99
 100 /* See run-on-main-thread.h.  */
 101
 102 bool
 103 is_main_thread ()
 104 {
 105 #if CXX_STD_THREAD
 106   /* Initialize main_thread_id on first use of is_main_thread.  */
 107   if (!main_thread_id_initialized)
 108     {
 109       main_thread_id_initialized = true;
 110
 111       main_thread_id = std::this_thread::get_id ();
 112     }
 113
 114   return std::this_thread::get_id () == main_thread_id;
 115 #else
 116   return true;
 117 #endif
 118 }
 119
 120 void _initialize_run_on_main_thread ();
 121 void
 122 _initialize_run_on_main_thread ()
 123 {
 124 #if CXX_STD_THREAD
 125   /* The variable main_thread_id should be initialized when entering main, or
 126      at an earlier use, so it should already be initialized here.  */
 127   gdb_assert (main_thread_id_initialized);
 128
 129   /* Assume that we execute this in the main thread.  */
 130   gdb_assert (is_main_thread ());
 131 #endif
 132   runnable_event = make_serial_event ();
 133   add_file_handler (serial_event_fd (runnable_event), run_events, nullptr,
 134                     "run-on-main-thread");
 135
 136   /* A runnable may refer to an extension language.  So, we want to
 137      make sure any pending ones have been deleted before the extension
 138      languages are shut down.  */
 139   add_final_cleanup ([] ()
 140     {
 141 #if CXX_STD_THREAD
 142       std::lock_guard lock (runnable_mutex);
 143 #endif
 144       runnables.clear ();
 145     });
 146 }