• WhatMeWorry (33/33) Mar 31 2022 I run the program (at the bottom) and get, as expected, the
• Paul Backus (9/11) Mar 31 2022 Closest you can get is probably [`GC.stats`][1], which will give
• Steven Schveighoffer (11/29) Mar 31 2022 Note that your code example is not hitting the limit of the largest

WhatMeWorry <kheaser gmail.com> writes:

I run the program (at the bottom) and get, as expected, the 
run-time out of memory error:

PS C:\D\sandbox> .\Reserve.exe
   newCapacity = [              1]
   newCapacity = [              3]
   newCapacity = [              5]
                 o    o    o
   newCapacity = [    905,207,293]
   newCapacity = [    905,207,805]
   newCapacity = [    905,208,317]

core.exception.OutOfMemoryError src\core\lifetime.d(126): Memory 
allocation failed


Is there a way to programmatically determine the exact maximum 
memory size available to the DRuntime’s array implementation?


import std.stdio;
import std.format;

void main()
{
     ulong[] big;
     size_t newCapacity;
     size_t oldCapacity;
	
     foreach(i; 0..ulong.max)
     {
         newCapacity = big.reserve(i);
         if(oldCapacity != newCapacity)
         {
             writeln("  newCapacity = ", format("[%15,3d]", 
newCapacity) );
             oldCapacity = newCapacity;
         }
     }
}

Paul Backus <snarwin gmail.com> writes:

On Thursday, 31 March 2022 at 19:44:23 UTC, WhatMeWorry wrote:
 Is there a way to programmatically determine the exact maximum 
 memory size available to the DRuntime’s array implementation?

Closest you can get is probably [`GC.stats`][1], which will give 
you the total amount of free memory available to the GC.

If what you actually want to do is attempt to grow an array 
without crashing if there isn't enough memory, you can use 
[`GC.extend`][2]. There's an example in the linked documentation 
that shows how to do it.

[1]: https://druntime.dpldocs.info/core.memory.GC.stats.html
[2]: https://druntime.dpldocs.info/core.memory.GC.extend.html

Steven Schveighoffer <schveiguy gmail.com> writes:

On 3/31/22 3:44 PM, WhatMeWorry wrote:
 I run the program (at the bottom) and get, as expected, the run-time out 
 of memory error:
 
 PS C:\D\sandbox> .\Reserve.exe
    newCapacity = [              1]
    newCapacity = [              3]
    newCapacity = [              5]
                  o    o    o
    newCapacity = [    905,207,293]
    newCapacity = [    905,207,805]
    newCapacity = [    905,208,317]
 
 core.exception.OutOfMemoryError src\core\lifetime.d(126): Memory 
 allocation failed
 
 
 Is there a way to programmatically determine the exact maximum memory 
 size available to the DRuntime’s array implementation?

Note that your code example is not hitting the limit of the largest 
contiguous block that could be allocated, but the sum of it and *all the 
smaller blocks*, as those are still used by the GC.

At any of those extensions, it might reallocate a new block, and copy 
the data there. In that case, the original block is abandoned (and might 
be freed to the GC), but it's not used in any subsequent allocations, 
because your new allocations won't fit! So the GC's usage of memory 
might be much higher than you think.

What I'd do is a binary search via *new processes* to see where it breaks.

-Steve