Is g_ptr_array_add () in GLib thread safe?

Question

The documentation says:

          void  g_ptr_array_insert (GPtrArray *array,
                gint index_,
                gpointer data);

Inserts an element into the pointer array at the given index. The array will grow in size automatically if necessary.

Same question for g_ptr_array_add().
Documentation is silent about thread safety of these functions. The following functions are described expressly to be thread-safe:

      g_ptr_array_free ()
      g_ptr_array_ref()
      g_ptr_array_unref ()

What if multiple-threads execute g_ptr_array_insert() at the same time on the same array of pointers? Do I have to provide thread safety myself?

Answer 1

No, it's not thread-safe (just as almost all GLib data types; source, see “you must coordinate accesses…”). Chances are that two threads enter marked line simultaneously.

static void
g_ptr_array_maybe_expand (GRealPtrArray *array,
                          gint           len)
{
  if ((array->len + len) > array->alloc)
    {
      guint old_alloc = array->alloc;
      array->alloc = g_nearest_pow (array->len + len);
      array->alloc = MAX (array->alloc, MIN_ARRAY_SIZE);
      array->pdata = g_realloc (array->pdata, sizeof (gpointer) * array->alloc); // here
      if (G_UNLIKELY (g_mem_gc_friendly))
        for ( ; old_alloc < array->alloc; old_alloc++)
          array->pdata [old_alloc] = NULL;
    }
}

void
g_ptr_array_add (GPtrArray *array,
                 gpointer   data)
{
  GRealPtrArray *rarray = (GRealPtrArray *)array;

  g_return_if_fail (rarray);

  g_ptr_array_maybe_expand (rarray, 1);

  rarray->pdata[rarray->len++] = data;
}

Provide your own locking using, for example, GMutex.