py: Add optional support for recursive mutexes, use for gc mutex.

Enabled by default if using threading and no GIL

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <[email protected]>

Author: projectgus

py/gc.c

@@ -113,9 +113,12 @@
 #endif
 
 #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))
+#define GC_MUTEX_INIT() mp_thread_recursive_mutex_init(&MP_STATE_MEM(gc_mutex))
+#define GC_ENTER() mp_thread_recursive_mutex_lock(&MP_STATE_MEM(gc_mutex), 1)
+#define GC_EXIT() mp_thread_recursive_mutex_unlock(&MP_STATE_MEM(gc_mutex))
 #else
+// Either no threading, or assume callers to gc_collect() hold the GIL
+#define GC_MUTEX_INIT()
 #define GC_ENTER()
 #define GC_EXIT()
 #endif
@@ -210,9 +213,7 @@ void gc_init(void *start, void *end) {
     MP_STATE_MEM(gc_alloc_amount) = 0;
     #endif
 
-    #if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
-    mp_thread_mutex_init(&MP_STATE_MEM(gc_mutex));
-    #endif
+    GC_MUTEX_INIT();
 }
 
 #if MICROPY_GC_SPLIT_HEAP

py/mpconfig.h

@@ -1629,6 +1629,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_THREAD_GIL_VM_DIVISOR (32)
 #endif
 
+// Is a recursive mutex type in use?
+#ifndef MICROPY_PY_THREAD_RECURSIVE_MUTEX
+#define MICROPY_PY_THREAD_RECURSIVE_MUTEX (MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL)
+#endif
+
 // Extended modules
 
 #ifndef MICROPY_PY_ASYNCIO

py/mpstate.h

@@ -145,7 +145,7 @@ typedef struct _mp_state_mem_t {
 
     #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;
+    mp_thread_recursive_mutex_t gc_mutex;
     #endif
 } mp_state_mem_t;
 

py/mpthread.h

@@ -48,6 +48,12 @@ void mp_thread_mutex_init(mp_thread_mutex_t *mutex);
 int mp_thread_mutex_lock(mp_thread_mutex_t *mutex, int wait);
 void mp_thread_mutex_unlock(mp_thread_mutex_t *mutex);
 
+#if MICROPY_PY_THREAD_RECURSIVE_MUTEX
+void mp_thread_recursive_mutex_init(mp_thread_recursive_mutex_t *mutex);
+int mp_thread_recursive_mutex_lock(mp_thread_recursive_mutex_t *mutex, int wait);
+void mp_thread_recursive_mutex_unlock(mp_thread_recursive_mutex_t *mutex);
+#endif
+
 #endif // MICROPY_PY_THREAD
 
 #if MICROPY_PY_THREAD && MICROPY_PY_THREAD_GIL