Implementing Lightweight Threads

We describe an implementation of a threads library that provides extremely lightweight threads within a single UNIX process while allowing fully concurrent access to system resources. The threads are lightweight enough so that they can be created quickly, there can be thousands present, and synchronization can be accomplished rapidly. These goals are achieved by providing user threads which multiplex on a pool of kernel-supported threads of control. This pool is managed by the library and will automatically grow or shrink as required to ensure that the process will make progress while not using an excessive amount of kernel resources. The programmer can also tune the relationship between threads and kernel supported threads of control. This paper focuses on scheduling and synchronizing user threads, and their interaction with UNIX signals in a multiplexing threads library.