Singular Update Queue

Problem

When the state needs to be updated by multiple concurrent clients, we need it to be safely updated with one-at-a-time changes. Consider the example of the Write-Ahead Log pattern. We need entries to be processed one at a time, even if several concurrent clients are trying to write. Generally, locks are used to protect against concurrent modifications. But if the tasks being performed are time-consuming, such as writing to a file, blocking all the other calling threads until the task is completed can have severe impact on the overall system throughput and latency. It is important to make effective use of compute resources, while still maintaining the guarantee of one-at-a-time execution.