Writing multi-threaded shared variable code is notoriously difficult because a given program can result in different possible executions due to non-determinism. Observed executions may also vary depending on the specific compiler and runtime system at hand. Many aspects of behavior are beyond the control of the programmer at the language's level of abstraction (e.g., compiler transformations), and as a result, debugging and performance tuning are very difficult tasks. In this position paper, we propose that the language implementation stack (compiler, runtime system) should be open, i.e., transparent, accountable, and interactive, so that the programmer may have direct access to invaluable information, and regain control over the behavior of the program in a given environment. © 2011 ACM.