Fully Read/Write Fence-Free Work-Stealing with Multiplicity
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Work-stealing is a popular technique to implement dynamic load balancing in a distributed manner. In this approach, each process owns a set of tasks that have to be executed. The owner of the set can put tasks in it and can take tasks from it to execute them. When a process runs out of tasks, instead of being idle, it becomes a thief to steal tasks from a victim. Thus, a work-stealing algorithm provides three high-level operations: Put and Take, which can be invoked only by the owner, and Steal, which can be invoked by a thief. One of the main targets when designing work-stealing algorithms is to make Put and Take as simple and efficient as possible. Unfortunately, it has been shown that any work-stealing algorithm in the standard asynchronous model must use expensive Read-After-Write synchronization patterns or atomic Read-Modify-Write instructions (e.g. Compare Swap or Test Set), which may be costly in practice. Thus, prior research has proposed idempotent work-stealing, a relaxation for which there are algorithms with Put and Take devoid of Read-Modify-Write atomic instructions and Read-After- Write synchronization patterns; however, Put uses fences among Write instructions, and Steal uses Compare Swap and fences among Read instructions. This paper considers work-stealing with multiplicity, a relaxation in which every task is taken by at least one operation, with the requirement that any process can extract a task at most once. Three versions of the relaxation are considered and fully Read/Write algorithms are presented in the standard asynchronous model, all of them devoid of Read-After-Write synchronization patterns; the last algorithm is also fully fence-free.
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