Three-phase commit adds a precommit phase between voting and the final commit decision. In the simplified timing model used by this exercise, that extra phase lets a participant decide after losing contact with the coordinator.
Design a ThreePhaseCommitParticipant class:
ThreePhaseCommitParticipant() creates a stateless simulator.String finalState(String[] messages) processes one participant's messages in order and returns its final state.
The participant starts in "initial". Apply these rules:
"prepare" changes "initial" to "ready"."precommit" changes "ready" to "precommit"."commit" changes "precommit" to "committed"."abort" changes any active state to "aborted"."timeout" changes "precommit" to "committed", but changes "initial" or "ready" to "aborted".
The states "committed" and "aborted" are terminal. Each input is a valid protocol trace: normal phase messages appear only in the state where they apply, and an "abort" or "timeout", when present, is the final message.
Example 1:
Input:
Output:
Explanation: The participant moves from initial to ready, then precommit, and finally committed.
Example 2:
Input:
Output:
Explanation: Reaching precommit means the unanimous prepare result was announced. Under the exercise's assumptions, the participant can commit when the coordinator times out.
Constraints
1 <= messages.length <= 4messages[i] is "prepare", "precommit", "commit", "abort", or "timeout".- Normal phase messages form a valid prefix of
prepare, precommit, commit. abort or timeout, when present, is the final message.- Return exactly one of
"initial", "ready", "precommit", "committed", or "aborted". - At most
100 calls are made to finalState per object, and calls are independent.
Simulate a Three-Phase Commit Participantmedium