With technology scaling, integrated circuits behave more unpredictably due to process variation, environmental changes and aging effects. Various variation-aware and adaptive design methodologies have been proposed to tackle this problem. Clearly, more effective solutions can be obtained if we are able to collect real-time information such as the actual propagation delay of critical paths when the circuit is running in normal function mode. Motivated by the above, in this paper, we propose a novel concurrent online delay measurement architecture for critical paths, namely CODA, to facilitate this task. Experimental results demonstrate high accuracy and practicality of the proposed technique.