Semantics of Futures in The Actor Model
In the Actor model, an expression of the form future
- When F receives a request R, then it checks to see if it has already received a response (that can either be a return value or a thrown exception) from evaluating
proceeding as follows: - If it already has a response V, then
- If V is a return value, then it is sent the request R.
- If V is an exception, then it is thrown to the customer of the request R.
- If it does not already have a response, then R is stored in the queue of requests inside the F.
- If it already has a response V, then
- When F receives the response V from evaluating
, then V is stored in F and - If V is a return value, then all of the queued requests are sent to V.
- If V is an exception, then it is thrown to the customer of the each queued request.
However, some futures can deal with requests in special ways to provide greater parallelism. For example, the expression 1 + future factorial(n) can create a new future that will behave like the number 1+factorial(n). This trick does not always work. For example the following conditional expression:
- if m>future factorial(n) then print("bigger") else print("smaller")
suspends until the future for factorial(n) has responded to the request asking if m is greater than itself.
Read more about this topic: Futures And Promises
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“The actor should not play a part. Like the Aeolian harps that used to be hung in the trees to be played only by the breeze, the actor should be an instrument played upon by the character he depicts.”
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“There are very many characteristics which go into making a model civil servant. Prominent among them are probity, industry, good sense, good habits, good temper, patience, order, courtesy, tact, self-reliance, many deference to superior officers, and many consideration for inferiors.”
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