_PyObject_DebugMallocStats(): Added some potentially expensive internal

consistency checks, enabled only in a debug (Py_DEBUG) build.  Note that
this never gets called automatically unless PYMALLOC_DEBUG is #define'd
too, and the envar PYTHONMALLOCSTATS exists.

diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 602b3c3b2c25792f2bea9945da9df76f6a2070b2..c39a8238b702f3e19bcb9979f2c6398141b42c68 100644 (file)
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -908,6 +908,31 @@ write4(void *p, ulong n)
        q[3] = (uchar)( n        & 0xff);
 }
 
+#ifdef Py_DEBUG
+/* Is target in the list?  The list is traversed via the nextpool pointers.
+ * The list may be NULL-terminated, or circular.  Return 1 if target is in
+ * list, else 0.
+ */
+static int
+pool_is_in_list(const poolp target, poolp list)
+{
+       poolp origlist = list;
+       assert(target != NULL);
+       if (list == NULL)
+               return 0;
+       do {
+               if (target == list)
+                       return 1;
+               list = list->nextpool;
+       } while (list != NULL && list != origlist);
+       return 0;
+}
+
+#else
+#define pool_is_in_list(X, Y) 1
+
+#endif /* Py_DEBUG */
+
 /* The debug malloc asks for 16 extra bytes and fills them with useful stuff,
    here calling the underlying malloc's result p:
 
@@ -1200,7 +1225,10 @@ printone(const char* msg, ulong value)
        return origvalue;
 }
 
-/* Print summary info to stderr about the state of pymalloc's structures. */
+/* Print summary info to stderr about the state of pymalloc's structures.
+ * In Py_DEBUG mode, also perform some expensive internal consistency
+ * checks.
+ */
 void
 _PyObject_DebugMallocStats(void)
 {
@@ -1262,15 +1290,23 @@ _PyObject_DebugMallocStats(void)
                /* visit every pool in the arena */
                for (j = 0; j < poolsinarena; ++j, base += POOL_SIZE) {
                        poolp p = (poolp)base;
+                       const uint sz = p->szidx;
+                       uint freeblocks;
+
                        if (p->ref.count == 0) {
                                /* currently unused */
                                ++numfreepools;
+                               assert(pool_is_in_list(p, freepools));
                                continue;
                        }
-                       ++numpools[p->szidx];
-                       numblocks[p->szidx] += p->ref.count;
-                       numfreeblocks[p->szidx] += NUMBLOCKS(p->szidx) -
-                                                  p->ref.count;
+                       ++numpools[sz];
+                       numblocks[sz] += p->ref.count;
+                       freeblocks = NUMBLOCKS(sz) - p->ref.count;
+                       numfreeblocks[sz] += freeblocks;
+#ifdef Py_DEBUG
+                       if (freeblocks > 0)
+                               assert(pool_is_in_list(p, usedpools[sz + sz]));
+#endif
                }
        }