First-class user-level threads

Brian D. Marsh, Michael L. Scott, Thomas J. LeBlanc, Evangelos P. Markatos

Research output: Chapter in Book/Report/Conference proceedingConference contribution

95 Scopus citations


It is often desirable, for reasons of clarity, portability, and efficiency, to write parallel programs in which the number of processes is independent of the number of available processors. Several modern operating systems support more than one process in an address space, but the overhead of creating and synchronizing kernel processes can be high. Many runtime environments implement lightweight processes (threads) in user space, but this approach usually results in second-class status for threads, making it difficult or impossible to perform scheduling operations at appropriate times (e.g. when the current thread blocks in the kernel). In addition, a lack of common assumptions may also make it difficult for parallel programs or library routines that use dissimilar thread packages to communicate with each other, or to synchronize access to shared data.We describe a set of kernel mechanisms and conventions designed to accord first-class status to user-level threads, allowing them to be used in any reasonable way that traditional kernel-provided processes can be used, while leaving the details of their implementation to user-level code. The key features of our approach are (1) shared memory for asynchronous communication between the kernel and the user, (2) software interrupts for events that might require action on the part of a user-level scheduler, and (3) a scheduler interface convention that facilitates interactions in user space between dissimilar kinds of threads. We have incorporated these mechanisms in the Psyche parallel operating system, and have used them to implement several different kinds of user-level threads. We argue for our approach in terms of both flexibility and performance.

Original languageEnglish (US)
Title of host publicationProceedings of the 13th ACM Symposium on Operating Systems Principles, SOSP 1991
Number of pages12
StatePublished - Dec 1 1991
Event13th ACM Symposium on Operating Systems Principles, SOSP 1991 - Pacific Grove, CA, United States
Duration: Oct 13 1991Oct 16 1991

Publication series

NameProceedings of the 13th ACM Symposium on Operating Systems Principles, SOSP 1991


Other13th ACM Symposium on Operating Systems Principles, SOSP 1991
Country/TerritoryUnited States
CityPacific Grove, CA

ASJC Scopus subject areas

  • Software


Dive into the research topics of 'First-class user-level threads'. Together they form a unique fingerprint.

Cite this