From ccc18f047d6669583cdf8ddd53ec41d026743a25 Mon Sep 17 00:00:00 2001
From: David Lechner <david@pybricks.com>
Date: Wed, 22 Jan 2020 11:19:37 -0600
Subject: [PATCH] py/gc: Don't include or init gc_mutex when GIL is enabled.

When threads and the GIL are enabled, then the GC mutex is not needed.  The
gc_mutex field is never used in this case because of:

    #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
    #define GC_ENTER() mp_thread_mutex_lock(&MP_STATE_MEM(gc_mutex), 1)
    #define GC_EXIT() mp_thread_mutex_unlock(&MP_STATE_MEM(gc_mutex))
    #else
    #define GC_ENTER()
    #define GC_EXIT()
    #endif

So, we can completely remove gc_mutex everywhere when MICROPY_PY_THREAD
&& !MICROPY_PY_THREAD_GIL.
---
 py/gc.c      | 2 +-
 py/mpstate.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/py/gc.c b/py/gc.c
index c763a839e..c18cd429f 100644
--- a/py/gc.c
+++ b/py/gc.c
@@ -161,7 +161,7 @@ void gc_init(void *start, void *end) {
     MP_STATE_MEM(gc_alloc_amount) = 0;
     #endif
 
-    #if MICROPY_PY_THREAD
+    #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
     mp_thread_mutex_init(&MP_STATE_MEM(gc_mutex));
     #endif
 
diff --git a/py/mpstate.h b/py/mpstate.h
index ab7d8c51b..9bb87f0ba 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -98,7 +98,7 @@ typedef struct _mp_state_mem_t {
     size_t gc_collected;
     #endif
 
-    #if MICROPY_PY_THREAD
+    #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
     // This is a global mutex used to make the GC thread-safe.
     mp_thread_mutex_t gc_mutex;
     #endif