Relations Between The Expressiveness of Different Forms of Future
Eager thread-specific futures can be straightforwardly implemented in terms of non-thread-specific futures, by creating a thread to calculate the value at the same time as creating the future. In this case it is desirable to return a read-only view to the client, so that only the newly created thread is able to resolve this future.
To implement implicit lazy thread-specific futures (as provided by Alice ML, for example) in terms in non-thread-specific futures, needs a mechanism to determine when the future's value is first needed (for example, the WaitNeeded construct in Oz). If all values are objects, then the ability to implement transparent forwarding objects is sufficient, since the first message sent to the forwarder indicates that the future's value is needed.
Non-thread-specific futures can be implemented in terms of thread-specific futures, assuming that the system supports message passing, by having the resolving thread send a message to the future's own thread. However, this could be argued to be unnecessary complexity: in programming languages based on threads, the most expressive approach appears to be to provide a combination of non-thread-specific futures, read-only views, and either a 'WaitNeeded' construct or support for transparent forwarding.
Read more about this topic: Futures And Promises
Famous quotes containing the words relations, forms and/or future:
“Think of the many different relations of form and content. E.g., the many pairs of trousers and what’s in them.”
—Mason Cooley (b. 1927)
“I am not so foolish as to declaim against forms. Forms are as essential as bodies; but to exalt particular forms, to adhere to one form a moment after it is outgrown, is unreasonable, and it is alien to the spirit of Christ.”
—Ralph Waldo Emerson (1803–1882)
“You have too much of a life yet before you, and have shown too much of promise as an officer, for your future to be lightly surrendered.”
—Abraham Lincoln (1809–1865)