Rename primary_thread to main_thread

This avoids the confusion of using two different phrases "main thread"
and "primary thread" internally to mean the same thing.  See:
http://lists.gnu.org/archive/html/emacs-devel/2016-12/msg01142.html
* src/thread.c (main_thread): Rename from primary_thread,
since the new name no longer clashes with main_thread_id
and Emacs internals normally call this the "main thread".
(init_main_thread): Rename from init_primary_thread.
(main_thread_p): Rename from primary_thread_p.
All uses changed.

src/alloc.c

@@ -6404,7 +6404,7 @@ mark_object (Lisp_Object arg)
 
 #ifdef GC_CHECK_MARKED_OBJECTS
 	m = mem_find (po);
-	if (m == MEM_NIL && !SUBRP (obj) && !primary_thread_p (po))
+	if (m == MEM_NIL && !SUBRP (obj) && !main_thread_p (po))
 	  emacs_abort ();
 #endif /* GC_CHECK_MARKED_OBJECTS */
 
@@ -6416,7 +6416,7 @@ mark_object (Lisp_Object arg)
 
 	if (pvectype != PVEC_SUBR
 	    && pvectype != PVEC_BUFFER
-	    && !primary_thread_p (po))
+	    && !main_thread_p (po))
 	  CHECK_LIVE (live_vector_p);
 
 	switch (pvectype)

src/thread.c

@@ -26,11 +26,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "coding.h"
 #include "syssignal.h"
 
-static struct thread_state primary_thread;
+static struct thread_state main_thread;
 
-struct thread_state *current_thread = &primary_thread;
+struct thread_state *current_thread = &main_thread;
 
-static struct thread_state *all_threads = &primary_thread;
+static struct thread_state *all_threads = &main_thread;
 
 static sys_mutex_t global_lock;
 
@@ -927,41 +927,41 @@ thread_check_current_buffer (struct buffer *buffer)
 
 
 static void
-init_primary_thread (void)
+init_main_thread (void)
 {
-  primary_thread.header.size
+  main_thread.header.size
     = PSEUDOVECSIZE (struct thread_state, m_stack_bottom);
-  XSETPVECTYPE (&primary_thread, PVEC_THREAD);
-  primary_thread.m_last_thing_searched = Qnil;
-  primary_thread.m_saved_last_thing_searched = Qnil;
-  primary_thread.name = Qnil;
-  primary_thread.function = Qnil;
-  primary_thread.error_symbol = Qnil;
-  primary_thread.error_data = Qnil;
-  primary_thread.event_object = Qnil;
+  XSETPVECTYPE (&main_thread, PVEC_THREAD);
+  main_thread.m_last_thing_searched = Qnil;
+  main_thread.m_saved_last_thing_searched = Qnil;
+  main_thread.name = Qnil;
+  main_thread.function = Qnil;
+  main_thread.error_symbol = Qnil;
+  main_thread.error_data = Qnil;
+  main_thread.event_object = Qnil;
 }
 
 bool
-primary_thread_p (void *ptr)
+main_thread_p (void *ptr)
 {
-  return (ptr == &primary_thread) ? true : false;
+  return ptr == &main_thread;
 }
 
 void
 init_threads_once (void)
 {
-  init_primary_thread ();
+  init_main_thread ();
 }
 
 void
 init_threads (void)
 {
-  init_primary_thread ();
-  sys_cond_init (&primary_thread.thread_condvar);
+  init_main_thread ();
+  sys_cond_init (&main_thread.thread_condvar);
   sys_mutex_init (&global_lock);
   sys_mutex_lock (&global_lock);
-  current_thread = &primary_thread;
-  primary_thread.thread_id = sys_thread_self ();
+  current_thread = &main_thread;
+  main_thread.thread_id = sys_thread_self ();
 }
 
 void

src/thread.h

@@ -285,7 +285,7 @@ extern void maybe_reacquire_global_lock (void);
 extern void init_threads_once (void);
 extern void init_threads (void);
 extern void syms_of_threads (void);
-extern bool primary_thread_p (void *);
+extern bool main_thread_p (void *);
 
 typedef int select_func (int, fd_set *, fd_set *, fd_set *,
 			 const struct timespec *, const sigset_t *);

src/w32.h

@@ -89,7 +89,7 @@ typedef struct _child_process
      terminate it by sys_kill.  */
   HWND                hwnd;
   /* Information about subprocess returned by CreateProcess.  Includes
-     handles to the subprocess and its primary thread, and the
+     handles to the subprocess and its main thread, and the
      corresponding process ID and thread ID numbers.  The PID is
      mirrored by the 'pid' member above.  The process handle is used
      to wait on it.  */