Antipattern in core.memory.GC.addRange?

safety0ff safety0ff.dev at gmail.com
Sat Sep 23 05:30:08 UTC 2017


On Friday, 22 September 2017 at 21:29:10 UTC, Steven 
Schveighoffer wrote:
> GC.addRange has this signature:
>
> static nothrow @nogc void addRange(in void* p, size_t sz, const 
> TypeInfo ti = null);
>
> I see a large problem with this. Let's say you malloc an array 
> of struct pointers:
>
> struct Foo { ... }
>
> import core.stdc.stdlib;
> auto ptrs = (cast(Foo *)malloc(Foo.sizeof * 10))[0 .. 10];
>
> Now, you want to store GC pointers in that block, you need to 
> add the range to the GC:
>
> GC.addRange(ptrs.ptr, ptrs.length);
>
> See the problem?

Yes, you forgot to multiply by Foo.sizeof.

Using the pattern from the example in the documentation,
the code would be:

size_t bytes = Foo.sizeof * 10;
auto ptrs = (cast(Foo *)malloc(bytes))[0 .. 10];
GC.addRange(ptrs.ptr, bytes);



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