From ec6196afeeefe83c9e717ea5fba7a2f81632680d Mon Sep 17 00:00:00 2001
From: Etienne Vouga <evouga@gmail.com>
Date: Sun, 13 Aug 2017 01:38:32 -0500
Subject: The keyboard handler has a race condition that can cause Allegro
 programs to stop accepting any keyboard input (usually manifests itself after
 the program has been running a considerable length of time). Replaced the old
 attempt at protecting the critical section with a mutex.


diff --git a/src/keyboard.c b/src/keyboard.c
index c433268a7f6a..34fced3d9f2f 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -134,6 +134,7 @@ typedef struct KEY_BUFFER
 static volatile KEY_BUFFER key_buffer;
 static volatile KEY_BUFFER _key_buffer;
 
+static void *key_mutex;
 
 
 /* add_key:
@@ -163,12 +164,7 @@ static INLINE void add_key(volatile KEY_BUFFER *buffer, int key, int scancode)
       }
    }
 
-   buffer->lock++;
-
-   if (buffer->lock != 1) {
-      buffer->lock--;
-      return;
-   }
+   system_driver->lock_mutex(key_mutex);
 
    if ((waiting_for_input) && (keyboard_driver) && (keyboard_driver->stop_waiting_for_input))
       keyboard_driver->stop_waiting_for_input();
@@ -184,7 +188,7 @@ static INLINE void add_key(volatile KEY_BUFFER *buffer, int key, int scancode)
       buffer->end = c;
    }
 
-   buffer->lock--;
+   system_driver->unlock_mutex(key_mutex);
 }
 
 
@@ -197,14 +193,12 @@ void clear_keybuf(void)
    if (keyboard_polled)
       poll_keyboard();
 
-   key_buffer.lock++;
-   _key_buffer.lock++;
+   system_driver->lock_mutex(key_mutex);
 
    key_buffer.start = key_buffer.end = 0;
    _key_buffer.start = _key_buffer.end = 0;
 
-   key_buffer.lock--;
-   _key_buffer.lock--;
+   system_driver->unlock_mutex(key_mutex);
 
    if ((keypressed_hook) && (readkey_hook))
       while (keypressed_hook())
@@ -400,6 +394,13 @@ END_OF_STATIC_FUNCTION(repeat_timer);
 {
    key_buffer.lock = _key_buffer.lock = 0;
 
+   // since this mode of using the keyboard handler does not have a removal
+   // function, it leaks memory---but at least we can limit the leak to only
+   // a single mutex even if the user calls this function a bunch of times
+   // for some reason.
+   if(!key_mutex)
+      key_mutex = system_driver->create_mutex();
+
    clear_keybuf();
    clear_key();
 
@@ -651,6 +652,9 @@ int install_keyboard(void)
    LOCK_FUNCTION(repeat_timer);
 
    key_buffer.lock = _key_buffer.lock = 0;
+   
+   if(!key_mutex)
+      key_mutex = system_driver->create_mutex();
 
    clear_keybuf();
    clear_key();
@@ -720,6 +724,11 @@ void remove_keyboard(void)
 
    clear_keybuf();
    clear_key();
+   
+   if(key_mutex) {
+      system_driver->destroy_mutex(key_mutex);
+      key_mutex = NULL;
+   }
 
    key_shifts = _key_shifts = 0;