Simplifying the Creation of Efficient Servers with Virtual Threads

Researchers:	Elaine Cheong
	Fred Reiss
Advisor:	Edward A. Lee

For serving web pages and performing other I/O-intensive tasks involving many concurrent users, single-process event-driven servers are generally more efficent than multi-threaded servers because the former have less context-switching overhead. Unfortunately, event-driven servers are difficult to write and to debug. When writing an event-driven server, the programmer is forced to divide the processing of a connection into discrete states and to handle passing of information between states. When debugging such a server, the programmer must derive the current status of all connections by hand from the data structures she devised while writing the server.

We propose a new development model for servers, Virtual Threads, which combines the efficiency of an event-driven server with the ease of implementation of a multithreaded server. In this model, developers write the code to handle a single connection as if it were a single thread in a multithreaded server. A preprocessor then generates an event-driven state machine from this straight-line code, annotating the generated code so that debuggers can refer to the original straight-line code. We will define a subset of the C language, vtC, that makes this conversion tractable and prove formally that converting vtC to a state machine is indeed possible. We will then write a preprocessor that does this conversion. We will use these development tools to implement a simple Web server.

Last updated 11/03/00