Code Quality Improvement - Session 37: Entanglement Between Long Lifecycles

We examine a design flaw using the FooBufferedLogger class, which buffers logs and sends them all at once, as an example. In the initial design, a separate instance was created for each tag and safely managed through the Closeable interface.

However, to reuse FooApiClient and hide tag management, the design was changed so that a single instance's internal state is modified by calling startLogging and finishLogging. This change led to an unexpected problem.

Due to the function call structure, when executeBar calls executeBaz, the startLogging called from the inner function overwrites the tag state of the outer function, resulting in a phenomenon of Spaghetti entanglement. As a result, the outer function's log data is lost or recorded under the wrong tag.

The root cause of this problem is that operations with different Lifecycles depend on a single object's state, becoming complexly entangled with one another.