| The traditional assumption about memory is that a read returns the value written by the most recent write. However in multiprocessing environments, the processes independently and simultaneously submit reads and writes resulting in a partial order of memory operations. In this partial order, the definition of most recent may be ambiguous. Memory consistency models were developed to formally specify the values that may be returned by read operations given that memory operations may be only partially ordered. Before this work, selecting a consistency model was seen as an off-line activity. Any particular program run would execute start to finish under a single consistency model. One hypothesis for many types of applications. In addition, these applications may want to change consistency at run-time. The class of collaboration application is used as an example of programs that may want to operate under different consistency at different points in their execution. A new lattice based framework of consistency models is defined that allows all useful consistency models in the literature to be defined by a combination of a common set of properties. This was not previously possible. Further, transitions between any two consistency models, as is needed in a collaboration system, can be described by a path in the lattice. In addition, a transition theory is presented specifying the allowable behavior of memory when a single program submits operations under more than one consistency model. |
