We present two systems, reliable sockets (rocks) and reliable packets (racks), that provide transparent network connection mobility using only user- level mechanisms. Each system can detect a connection failure within seconds of its occurrence, preserve the endpoint of a failed connection in a suspended state for an arbitrary period of time, and automatically reconnect, even when one end of the connection changes IP address, with correct recovery of in-flight data. To allow rocks and racks to interoperate with ordinary clients and servers, we introduce a general user-level Enhancement Detection Protocol that enables the remote detection of rocks and racks, or any other socket enhancement system, but does not affect applications that use ordinary sockets. Rocks and racks provide the same functionality but have different implementation models: rocks intercept and modify the behavior of the sockets API by using an interposed library, while racks uses a packet filter to intercept and modify the packets exchanged over a connection. Racks and rocks introduce small throughput and latency overheads that we deem acceptable for the level of mobility and reliability they provide.

Process checkpointing is a basic mechanism required for providing high throughput computing service on distributively owned resources. We present a new process checkpoint and migration technique, called process hijacking, that uses dynamic program re-writing techniques to add checkpointing capability to a running program. Process hijacking makes it possible to checkpoint and migrate proprietary applications that cannot be re-linked with a checkpoint library, and it makes it possible to dynamically hand off an ordinary running process to a distributed resource management system such as Condor. We discuss the problems of adding checkpointing capability to a program already in execution: loading new code into the running process; and replacing functions of the process with calls to dynamically loaded functions. We use the DynInst API process editing library, augmented with a new call for replacing functions, to solve these problems.