Read-copy update grace period detection without atomic instructions that gracefully handles large numbers of processors

A computer program product for avoiding unnecessary grace period token processing while detecting a grace period for deferring removal of a shared data element until pre-existing references to the data element are removed, comprising:

• one or more data storage media;
• programming means recorded on said data storage media for programming a data processing platform to operate as by:
• establishing a token to be circulated between processing entities sharing access to said data element;
• said token being indicative of a grace period having elapsed when said token makes a round trip through said processing entities;
• associating a distributed indicator with each of said processing entities that is indicative of whether there is a need to perform removal processing at any of said processing entities relative to any data element shared by said processing entities;
• processing said distributed indicator at each of said processing entities before engaging in token processing at said processing entities;
• and
• performing token processing at said processing entities only when warranted by said distributed indicator.

A data processing system having one or more processors, a memory and a communication pathway between the one or more processors and the memory, said system including a read-copy update subsystem adapted to avoid unnecessary grace period token processing while detecting a grace period to determine when pending callbacks may be executed, and comprising:

• means for implementing a quiescent state counter at each of a set of processors sharing access to said a data element;
• means for establishing a grace period token as a discontinuity in count values maintained by said quiescent state counters;
• said token being indicative of a grace period having elapsed at one of said processors when said token makes a round trip through said set of processors to return to said one of said processors;
• means for associating a distributed callback indicator as a local variable in a cache memory associated with each of said processors that is indicative of whether there is a need to process said callbacks at any of said processors;
• means for processing said distributed callback indicator at each of said processors before engaging in token processing at said processors;
• and
• means for performing token processing at said processors only when warranted by said distributed callback indicator.