Token Based Group Mutual Exclusion for Asynchronous Rings
نویسندگان
چکیده
The mutual exclusion and concurrency are among the fundamental problems of distributed systems. The mutual exclusion ensures an exclusive access to a shared resource among a set of processes. The concurrency allows some processes to share a resource. The group mutual exclusion (GME) problem [1] deals with both mutual exclusion and concurrency. The GME solution allows n processes to share m mutually exclusive resources labeled in f1; : : : ;mg. At any time, some processes share a particular resource. But, if some process requests to access a resource different from the currently used resource, then the process cannot access the requested resource at that time. However, if a process requests the same resource (i.e., the currently used resource), it is allowed to share the resource. There is no limit on the number of processes which can use the resource. An interesting application of the group mutual exclusion is presented in [1]. Consider large data sets stored in a secondary memory. A set of processes accesses to the data sets through a server. The server can be a CD jukebox. Using a regular mutual exclusive protocol, the server needs to repeatedly load and unload the data sets (e.g., the CDs) from the secondary memory to process the requests. An efficient GME protocol would allow multiple processes to read the currently loaded data set (a CD) concurrently, while forcing processes requesting a different data set (another CD) to wait. Furthermore, while a data set remains loaded, this set remains accessible to processes requesting that set until some other data sets are requested by some process. An efficient GME solution could also help improve the quality of services of an Internet server. The GME protocol can be used to group different requests for the same service, and thereby, minimize the memory swapping.
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