Apparatus and method for achieving reduced overhead mutual-exclusion and maintaining coherency in a multiprocessor system utilizing execution history and thread monitoring
First Claim
1. A method of using an updater thread to update an original element of a shared data structure in a computer system while maintaining access to the data structure for reader threads, the method comprising the following steps:
- with an updater thread, updating the original element by creating a new element;
with the updater thread, modifying links used by reader threads for referencing the original element to now reference the new element; and
using a summary of thread activity to determine when the original element may be erased.
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Abstract
A substantially zero overhead mutual-exclusion apparatus and method (90, 120) is provided that allows concurrent reading and updating data while maintaining data coherency. That is, a data reading process executes the same sequence of instructions that would be executed if the data were never updated. Rather than depending exclusively on overhead-imposing locks, this mutual-exclusion mechanism tracks an execution history (138) of a thread (16, 112) to determine safe times for processing a current generation (108, 130, 131) of data updates while a next generation (110, 132, 133) of data updates is concurrently being saved. A thread is any locus of control, such as a processor. A summary of thread activity (106, 122) tracks which threads have passed through a quiescent state after the current generation of updates was started. When the last thread related to the current generation passes through a quiescent state, the summary of thread activity signals a callback processor (104, 124) that it is safe to end the current generation of updates. The callback processor then processes and erases all updates in the current generation. The next generation of updates then becomes the current generation of updates. The callback processor restarts the summary of thread activity and initiates a new next generation of updates. All data-updating threads pass through a quiescent state between the time they attempt to update data and the time the data are actually updated.
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Citations
11 Claims
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1. A method of using an updater thread to update an original element of a shared data structure in a computer system while maintaining access to the data structure for reader threads, the method comprising the following steps:
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with an updater thread, updating the original element by creating a new element; with the updater thread, modifying links used by reader threads for referencing the original element to now reference the new element; and using a summary of thread activity to determine when the original element may be erased. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Apparatus for using an updater thread to update an original element of a shared data structure in a computer system while maintaining access to the data structure for reader threads, comprising:
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means for updating with an updater thread the original element by creating a new element; means for modifying with the updater thread links used by reader threads for referencing the original element to now reference the new element; and means for using a summary of thread activity to determine when the original element may be erased. - View Dependent Claims (10, 11)
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Specification