Skip to main content
Kent Academic Repository

Higher levels of process synchronisation

Welch, Peter H. and Wood, David C. (1997) Higher levels of process synchronisation. In: Bakkers, A.W.P., ed. Parallel Programming and Java. Concurrent Systems Engineering Series, 50 . I O S Press, pp. 104-129. ISBN 90-5199-336-6. (KAR id:18035)


Four new synchronisation primitives (SEMAPHOREs, RESOURCEs, EVENTs and BUCKETs) were introduced in the KRoC 0.8beta release of occam for SPARC (SunOS/Solaris) and Alpha (OSF/1) UNIX workstations [1][2][3]. This paper reports on the rationale, application and implementation of two of these (SEMAPHOREs and EVENTs). Details on the other two may be found on the web [4]. The new primitives are designed to support higher-level mechanisms of SHARING between parallel processes and give us greater powers of expression. They will also let greater levels of concurrency be safely exploited from future parallel architectures, such as those providing (virtual) shared-memory. They demonstrate that occam is neutral in any debate between the merits of message-passing versus shared-memory parallelism, enabling applications to take advantage of whichever paradigm (or mixture of paradigms) is the most appropriate. The new primitives could be (but are not) implemented in terms of traditional channels, but only at the expense of increased complexity and computational overhead. The primitives are immediately useful even for uni-processors - for example, the cost of a fair ALT can be reduced from O(n) to O(1). In fact, all the operations associated with new primitives have constant space and time complexities; and the constants are very low. The KRoC release provides an Abstract Data Type interface to the primitives. However, direct use of such mechanisms still allows the user to misuse them. They must be used in the ways prescribed (in this paper and in [4]) else their semantics become unpredictable. No tool is provided to check correct usage at this level. The intention is to bind those primitives found to be useful into higher level versions of occam. Some of the primitives (e.g. SEMAPHOREs) may never themselves be made visible in the language, but may be used to implement bindings of higher-level paradigms (such as SHARED channels and BLACKBOARDs). The compiler will perform the relevant usage checking on all new language bindings, closing the security loopholes opened by raw use of the primitives. The paper closes by relating this work with the notions of virtual transputers, microcoded schedulers, object orientation and Java threads.

Item Type: Book section
Additional information: ISSN 1383-757
Subjects: T Technology > T Technology (General)
Divisions: Divisions > Division of Computing, Engineering and Mathematical Sciences > School of Computing
Depositing User: T.J. Sango
Date Deposited: 29 Apr 2009 13:24 UTC
Last Modified: 16 Nov 2021 09:56 UTC
Resource URI: (The current URI for this page, for reference purposes)

University of Kent Author Information

Welch, Peter H..

Creator's ORCID:
CReDIT Contributor Roles:

Wood, David C..

Creator's ORCID:
CReDIT Contributor Roles:
  • Depositors only (login required):

Total unique views for this document in KAR since July 2020. For more details click on the image.