• via Digitalmars-d-bugs (63/63) Aug 07 2015 https://issues.dlang.org/show_bug.cgi?id=14886

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=14886

          Issue ID: 14886
           Summary: std.parallelism.parallel with large static array seems
                    to hang compile
           Product: D
           Version: D2
          Hardware: x86
                OS: All
            Status: NEW
          Keywords: performance
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: schveiguy yahoo.com

example:

import std.parallelism;

void main()
{
   int x[100_000];
   parallel(x);
}

If you remove one 0 from the number of elements, the compile finishes with an
error:

/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/parallelism.d-mixin-3780(3878):
Error: template std.range.primitives.popFront cannot deduce function from
argument types !()(int[10000]), candidates are:
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/range/primitives.d(2032):  
     std.range.primitives.popFront(T)(ref T[] a) if (!isNarrowString!(T[]) &&
!is(T[] == void[]))
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/range/primitives.d(2055):  
     std.range.primitives.popFront(C)(ref C[] str) if (isNarrowString!(C[]))
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/parallelism.d-mixin-3780(3867):
Error: function
std.parallelism.ParallelForeach!(int[10000]).ParallelForeach.opApply.doIt.makeTemp
no return exp; or assert(0); at end of function
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/parallelism.d-mixin-3792(3890):
Error: template std.range.primitives.popFront cannot deduce function from
argument types !()(int[10000]), candidates are:
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/range/primitives.d(2032):  
     std.range.primitives.popFront(T)(ref T[] a) if (!isNarrowString!(T[]) &&
!is(T[] == void[]))
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/range/primitives.d(2055):  
     std.range.primitives.popFront(C)(ref C[] str) if (isNarrowString!(C[]))
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/parallelism.d-mixin-3792(3879):
Error: function
std.parallelism.ParallelForeach!(int[10000]).ParallelForeach.opApply.doIt.makeTemp
no return exp; or assert(0); at end of function
/Users/steves/git/dmd2/osx/bin/../../src/phobos/std/parallelism.d(3303): Error:
template instance std.parallelism.ParallelForeach!(int[10000]) error
instantiating
testarray.d(6):        instantiated from here: parallel!(int[10000])

I'm unsure if this is a bug in the compiler or a bug in std.parallelism. I
don't know how the latter is designed to work, but it does appear that there
isn't a valid instantiation for it, so I would suspect a compiler issue.

The timing seems to be non-linear based on the number of elements:

10k elements: 1.5 seconds to reach error
20k elements: 5.2 seconds to reach error
30k elements: 12.2 seconds to reach error
40k elements: 20.9 seconds to reach error
50k elements: 32.9 seconds to reach error

I stopped after that :)

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