[concurrency-interest] Implicit parallelism

Dane Foster studdugie at gmail.com
Fri Aug 23 13:34:21 EDT 2013


There are [research] languages like Fortress where parallelism is implicit
and where sequential behavior is the thing you must be explicit about.

Dane


On Fri, Aug 23, 2013 at 12:43 PM, Brian Goetz <brian at briangoetz.com> wrote:

> For what its worth, we've made the follwing choice in the JDK libraries:
> No Implicit Parallelism.  We can make parallelism unobtrusive, but we won't
> be making it implicit.
>
> Of course, other library writers can make their own choices.
>
> On 8/10/2013 2:45 PM, Gustav Åkesson wrote:
>
>> Hi guys,
>>
>> My discussion here concerns implicit parallelism. Let's say we have the
>> following setup:
>>
>> @Immutable
>> public class Integer
>> {
>>    ...
>> }
>>
>> @Immutable
>> public class ImmutableArrayList
>> {
>>     ...
>> }
>>
>> I'm looking for a way so that the parallelism would be introduced
>> without hard-coding anything related to parallelism (i.e. not stating
>> anything like .parallel or .par on the collection). Only thing needed
>> would be something annotation-ish which tells the execution environment
>> that this datastructure with elements is inherently thread-safe. Then
>> the execution could determine if it would be beneficial to do so. For
>> instance, for a structure with e.g. five elements, then it would not,
>> but for millions of elements, it would most likely be. Perhaps it could
>> even find some kind of sweet-spot of number of elements in which the
>> parallel overhead exceeds the benefits.
>>
>> Let's say we wish to sum all the integers in an ImmutableArrayList
>> (setup below), would it be possible for the compiler (javac, scalac or
>> what have you) and JVM to conspire and decide "hey, let's run this in
>> parallel since it doesn't violate application semantics and it can/will
>> be faster"? Is there any research in this area in regards to the JVM?
>>
>>
>> Best Regards,
>>
>> Gustav Åkesson
>>
>>
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