Indeed, the implementation in patch also contains heartbeat mechanism - the monitored process periodically sending heartbeat.
The different is a conventional heartbeat failure detector has a fixed timeout. The phi accrual failure detector decomposes functions into different components (monitoring, interpretation, etc.); with a suspicion level (not binary trust or suspect value output) exposed so that different applications equipped with its own interpreter can use the output value for further decision. For instance, a master may allocate urgent tasks to workers which have lower suspicion level. Or the monitoring process may interpret according to its business logic in determining if monitored process has crashed.
Although a task failure can be solved with a restart, the difficulty lies in the distinguished between a crash/ failure process and a very slow one. In addition, in the future if the project needs the feature of fault tolerant between bspmasters, a failure detection service is required.