A distributed queue does not have to delete a message as soon as a consumer receives it. Instead, it can hide the message for a visibility timeout. If the consumer acknowledges the message, the broker deletes it. If the consumer crashes without acknowledging, the timeout expires and the message becomes available for redelivery.
In this exercise, one message is never acknowledged.
Design a VisibilityTimeoutQueue class:
VisibilityTimeoutQueue(int timeout) creates a queue whose message starts visible at timestamp 0.boolean receive(int timestamp) attempts to receive the message at timestamp.
A receive succeeds when the message is visible. A successful receive returns true and hides the message until timestamp + timeout. A receive before that time returns false and must not change the current visibility deadline.
Calls use non-decreasing timestamps. When timestamp is exactly the visibility deadline, the timeout has expired and the receive succeeds.
Example 1:
Input:
Output:
Explanation: The receive at 0 hides the message until 10, so the attempt at 5 fails. At 20 the message is visible and becomes hidden until 30, so the attempt at 25 fails.
Example 2:
Input:
Output:
Explanation: Every receive occurs exactly when the preceding timeout expires. The visibility boundary is inclusive, so every call succeeds.
Constraints
1 <= timeout <= 10^90 <= timestamp <= 10^9- Calls to
receive use non-decreasing timestamps. - The message is never acknowledged or deleted.
- At most
10^5 calls are made to receive.
Simulate a Queue Visibility Timeoutmedium