dlmalloc: avoid unnecessary atomics in realloc()

* Atomics are much cheaper than mutexes for such rarely contented
  fields, but they are still much slower than plain arithmetics.
* For realloc(), we'd expect relatively small changes between calls
  which means that the chunk's usable size probably won't change.
  Therefore it makes sense to check whether we'd get a zero addition
  to teco_memory_usage.
* We will now have at most one atomic add in realloc() instead of
  always 2 atomic operations.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/memory.c b/src/memory.c
index d8de483..97bc627 100644
--- a/src/memory.c
+++ b/src/memory.c
@@ -338,11 +338,11 @@ calloc(size_t nmemb, size_t size)
 void * __attribute__((used))
 realloc(void *ptr, size_t size)
 {
-	if (ptr)
-		g_atomic_int_add(&teco_memory_usage, -dlmalloc_usable_size(ptr));
+	gssize len = ptr ? dlmalloc_usable_size(ptr) : 0;
 	ptr = dlrealloc(ptr, size);
-	if (G_LIKELY(ptr != NULL))
-		g_atomic_int_add(&teco_memory_usage, dlmalloc_usable_size(ptr));
+	gssize delta = (G_LIKELY(ptr != NULL) ? (gssize)dlmalloc_usable_size(ptr) : 0) - len;
+	if (delta != 0)
+		g_atomic_int_add(&teco_memory_usage, delta);
 	return ptr;
 }