Object and native code thread mobility among heterogeneous computers

We present a technique for moving objects and threads among heterogeneous computers at the native code level. To enable mobility of threads running native code. we convert thread states among machine-dependent and machine-independent formats. We introduce the concept of bus stops, which are machine-independent representations of program points as represented by program counter values. The concept of bus stops can be used also for other purposes. e.g. to aid inspecting and debugging optimized code, garbage collection etc. We also discuss techniques for thread mobility among processors executing differently optimized codes. We demonstrate the viability of our ideas by providing a prototype implementation of object and thread mobility among heterogeneous computers. The prototype uses the Emerald distributed programming language without modification ; we have merely extended the Emerald runtime system and the code generator of the Emerald compiler. Our extensions allow object and thread mobility among VAX, Sun-3, HP9000/300, and Sun SPARC workstations. The excellent intra-node performance of the original homogeneous Emerald is retained : migrated threads run at native code speed before and after migration ; the same speed as on homogeneous Emerald and close to C code performance. Our implementation of mobility has not been optimized : thread mobility and trans-architecture invocations take about 60% longer than in the homogeneous implementation. We believe this is the first implementation of full object and thread mobility among heterogeneous computers with threads executing native code.