implement reader_cancel_thread using __thread thread-local storage

reader.cpp

@@ -181,7 +181,10 @@ commence.
 #define SEARCH_FORWARD 1
 
 /* Any time the contents of a buffer changes, we update the generation count. This allows for our background highlighting thread to notice it and skip doing work that it would otherwise have to do. */
-static unsigned int s_generation_count;
+static volatile unsigned int s_generation_count;
+
+/* This threadlocal generation count is set when an autosuggestion background thread starts up, so it can easily check if the work it is doing is no longer useful. */
+static __thread unsigned int thread_generation_count;
 
 /* A color is an int */
 typedef int color_t;
@@ -667,6 +670,12 @@ int reader_reading_interrupted()
     return res;
 }
 
+bool reader_cancel_thread()
+{
+    ASSERT_IS_BACKGROUND_THREAD();
+    return s_generation_count != thread_generation_count;
+}
+
 void reader_write_title()
 {
     const wchar_t *title;
@@ -1225,6 +1234,8 @@ struct autosuggestion_context_t
             return 0;
         }
 
+        thread_generation_count = generation_count;
+
         /* Let's make sure we aren't using the empty string */
         if (search_string.empty())
         {

reader.h

@@ -132,6 +132,14 @@ void reader_reset_interrupted();
 */
 int reader_reading_interrupted();
 
+/**
+   Returns true if the current reader generation count does not equal the 
+   generation count the current thread was started with. 
+   Note: currently only valid for autocompletion threads! Other threads don't
+   set the threadlocal generation count when they start up. 
+*/
+bool reader_cancel_thread();
+
 /**
    Read one line of input. Before calling this function, reader_push()
    must have been called in order to set up a valid reader

wildcard.cpp

@@ -728,7 +728,7 @@ static int wildcard_expand_internal(const wchar_t *wc,
 
     //  debug( 3, L"WILDCARD_EXPAND %ls in %ls", wc, base_dir );
 
-    if (is_main_thread() && reader_interrupted())
+    if (is_main_thread() ? reader_interrupted() : reader_cancel_thread())
     {
         return -1;
     }