Global InformationFutures and promises information
In computer science, future, promise, delay, and deferred refer to constructs used for synchronizing program execution in some concurrent programming languages. They describe an object that acts as a proxy for a result that is initially unknown, usually because the computation of its value is not yet complete.
The term promise was proposed in 1976 by Daniel P. Friedman and David Wise,[1] and Peter Hibbard called it eventual.[2] A somewhat similar concept future was introduced in 1977 in a paper by Henry Baker and Carl Hewitt.[3]
The terms future, promise, delay, and deferred are often used interchangeably, although some differences in usage between future and promise are treated below. Specifically, when usage is distinguished, a future is a read-only placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the future. Notably, a future may be defined without specifying which specific promise will set its value, and different possible promises may set the value of a given future, though this can be done only once for a given future. In other cases a future and a promise are created together and associated with each other: the future is the value, the promise is the function that sets the value – essentially the return value (future) of an asynchronous function (promise). Setting the value of a future is also called resolving, fulfilling, or binding it.
- ^ Friedman, Daniel; David Wise (1976). The Impact of Applicative Programming on Multiprocessing. International Conference on Parallel Processing. pp. 263–272.
Preliminary version of: Friedman, Daniel; Wise, David (April 1978). "Aspects of Applicative Programming for Parallel Processing". IEEE Transactions on Computers. C-27 (4): 289–296. CiteSeerX 10.1.1.295.9692. doi:10.1109/tc.1978.1675100. S2CID 16333366. - ^ Hibbard, Peter (1976). Parallel Processing Facilities. New Directions in Algorithmic Languages, (ed.) Stephen A. Schuman, IRIA, 1976.
- ^ Henry Baker; Carl Hewitt (August 1977). The Incremental Garbage Collection of Processes. Proceedings of the Symposium on Artificial Intelligence Programming Languages. ACM SIGPLAN Notices 12, 8. pp. 55–59. Archived from the original on 4 July 2008. Retrieved 13 February 2015.