Process migration in distributed systems

This thesis discusses process migration in message-based systems and procedure-oriented systems. The issues that we deal with are the correctness of process migration and the design of migration schemes. The design goal of the migration schemes is to maintain migration transparency.;A formal user and environment interaction model is given for procedure-oriented systems. The execution environment of a user process is decomposed into environment objects. Environment objects are specified as state machines. System calls are external operations of environment objects. We argue that the transparency of process migration depends on how much knowledge a process has about its environment objects. The notion of environment view is introduced to distinguish what a user process can observe about its environment from the state of its environment. Two correctness criteria are proposed for maintaining migration transparency. The state consistency criterion requires that the internal state of a process at suspension time is kept the same until its resumption time. The view consistency criterion requires that the environment view of a process at any time after its migration must be consistent with its view at suspension time. Two migration schemes are designed for procedure-oriented systems. The implementation design of the two schemes are demonstrated in UNIX environment as examples.;In message-based systems, the key issue in process migration is to ensure reliable interprocess communication, namely, to ensure that messages are delivered correctly. Three migration schemes are discussed to ensure reliable user communications. Two protocols used for message loss prevention scheme are designed to support process migration in message-based systems.