From 2fe841d2fa022bc7f546ddd77a79eaa0150bdf87 Mon Sep 17 00:00:00 2001
From: Dave Hylands <dhylands@gmail.com>
Date: Mon, 30 Jun 2014 22:49:21 -0700
Subject: [PATCH] Try not to cause a MemoryError when raising an exception
 during nterrupt handling.

Step 1 fixes #732
---
 py/gc.c        | 4 ++++
 py/gc.h        | 1 +
 py/objexcept.c | 5 +++++
 3 files changed, 10 insertions(+)

diff --git a/py/gc.c b/py/gc.c
index 65bfea0b35..7aa5bc326e 100644
--- a/py/gc.c
+++ b/py/gc.c
@@ -172,6 +172,10 @@ void gc_unlock(void) {
     gc_lock_depth--;
 }
 
+bool gc_is_locked(void) {
+    return gc_lock_depth != 0;
+}
+
 #define VERIFY_PTR(ptr) ( \
         (ptr & (BYTES_PER_BLOCK - 1)) == 0          /* must be aligned on a block */ \
         && ptr >= (machine_uint_t)gc_pool_start     /* must be above start of pool */ \
diff --git a/py/gc.h b/py/gc.h
index cea368f480..3b3b7dbb50 100644
--- a/py/gc.h
+++ b/py/gc.h
@@ -30,6 +30,7 @@ void gc_init(void *start, void *end);
 // They can be used to prevent the GC from allocating/freeing.
 void gc_lock(void);
 void gc_unlock(void);
+bool gc_is_locked(void);
 
 // A given port must implement gc_collect by using the other collect functions.
 void gc_collect(void);
diff --git a/py/objexcept.c b/py/objexcept.c
index 9f421373bb..b4a831c628 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -37,6 +37,7 @@
 #include "objtype.h"
 #include "runtime.h"
 #include "runtime0.h"
+#include "gc.h"
 
 typedef struct _mp_obj_exception_t {
     mp_obj_base_t base;
@@ -335,6 +336,10 @@ void mp_obj_exception_clear_traceback(mp_obj_t self_in) {
 }
 
 void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, machine_uint_t line, qstr block) {
+    if (gc_is_locked()) {
+        // We can't allocate memory, so don't bother to try
+        return;
+    }
     GET_NATIVE_EXCEPTION(self, self_in);
 
     // for traceback, we are just using the list object for convenience, it's not really a list of Python objects