Concurrent Futures

Rob Withers reefedjib at
Sun Oct 28 02:37:35 UTC 2007

Hi Peter,  It struck me that I should clarify something I said, that 
probably misled you.

> Rob Withers wrote:
>> That's a nice example.  The difference with E's promises is that a 
>> Promise doesn't block for value, it sends the new msg eventually and 
>> returns a second promise.  The way I have this implemented in SqueakElib, 
>> is you send #eventual to get an eventual ref, then you can send a msg to 
>> the eventual ref, returning a promise, which you can then send a second 
>> msg to, returning a second promise.
>> | promise1 promise2 |
>> promise1 := anObject eventual foo.
>> promise2 := promise1 bar.
>> promise1 whenResolved: [:val | Transcript show: ' foo: ', val 
>> printString].
>> promise2 whenResolved: [:val | Transcript show: ' bar: ', val 
>> printString].
>> Transcript show: 'sent foo bar...'
>> This prevents deadlocks.

>From the first paragraph, I talk about both E and SqueakElib.  When I make 
this claim about eventual refs and promises preventing deadlocks, I mean it 
does this for E, not for SqueakElib.  Since E processes msg sends in an 
event-loop, they have no Processes nor Semaphores.  Since they restrict 
scope when compiling and executing code, so you can't even reference them. 
There is no way to block in E.

This is what I aspire to with SqueakElib but it won't make it, except 
perhaps in a very constrained environment, namely a restricted scope Island. 
An Island that likewise does not include Processes nor Semaphore (nor lots 
of other stuff that may use them, internally).  In the general case, which I 
am interested in, I want to integrate refs and promises in the general 
image, with its Processes and Semaphores.  I may need to block for immediate 
values, processing primitives with promises and processing method contexts 
which include promises with multiple points of return.  I am going to be 
blocking and I make, or I intent to make, no claim that I don't block.

Sorry for the confusion,

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