We present a novel notion of deadlock for tasks which synchronize on arbitrary boolean conditions and a sound deadlock analysis for it. Contrary to other approaches, our analysis aims to detect dead- locks caused by faulty system design, rather than implementation bugs. A deadlock is a circular dependency between multiple tasks, where a task dependents on a second task, if the execution of this second task enables the first one to resume. This requires the analysis of the side- effects of the computations. The analysis is implemented as an extension to the DECO tool, evaluated for the full coreABS language and uses the KeY-ABS theorem prover to reason about side-effects of computations.