Asynchronous Communication Using Synchronous IPC Primitives

The asynchronous communication model provides applications with parallelism, message buffering, and a convenient programming model. In contrast to the synchronous model however, it is inherently associated with policy regarding the management and delivery of buffered messages. Communication partners are dependent on controlling these policies in order to achieve additional semantics and performance optimizations customized to their communication behavior. Many existing operating systems implement asynchronous IPC primitives at kernel level but suffer from significant performance penalties compared to synchronous systems. Also, buffer management policies are hidden from the applications. Communication frameworks focusing on performance achieve high throughput even across multiple protection domains. However, they also imply memory management related policies and custom application trade-offs between throughput and latency are not possible. This thesis describes how the advantages of both communication models can be combined by emulating asynchronous communication on top of synchronous IPC primitives. It discusses the emulation with regard to performance, trust and protection between the involved communication partners, and transparency towards existing protocols. The presented concepts are evaluated on the L4 micro kernel. It is shown that asynchronous communication is achievable at user level with performance comparable to the synchronous IPC it is based on while preserving protocol transparency and flexibility for application specific policies.