More fun with toStringz and the GC

[Don Allen]

On Saturday, 6 August 2022 at 13:40:12 UTC, Don Allen wrote:
> On Saturday, 6 August 2022 at 02:14:24 UTC, Steven 
> Schveighoffer wrote:
>> On 8/5/22 8:51 PM, Don Allen wrote:
>>
>>> And this, from Section 32.2 of the Language Reference Manual:
>>> ````
>>> If pointers to D garbage collector allocated memory are 
>>> passed to C functions, it's critical to ensure that the 
>>> memory will not be collected by the garbage collector before 
>>> the C function is done with it. This is accomplished by:
>>> 
>>>      Making a copy of the data using 
>>> core.stdc.stdlib.malloc() and passing the copy instead.
>>>      -->Leaving a pointer to it on the stack (as a parameter 
>>> or automatic variable), as the garbage collector will scan 
>>> the stack.<--
>>>      Leaving a pointer to it in the static data segment, as 
>>> the garbage collector will scan the static data segment.
>>>      Registering the pointer with the garbage collector with 
>>> the std.gc.addRoot() or std.gc.addRange() calls.
>>> ````
>>> I did what the documentation says and it does not work.
>>
>> I know, I felt exactly the same way in my post on it:
>>
>> https://forum.dlang.org/post/sial38$7v0$1@digitalmars.com
>>
>> I even issued a PR to remove the problematic recommendation:
>>
>> https://github.com/dlang/dlang.org/pull/3102
>>
>> But there was pushback to the point where it wasn't worth it. 
>> So I closed it.
>
> As I said in my previous post, the documentation issue really 
> needs to be addressed.
>
> I do realize now that I *assumed* that what I did was going to 
> result in a stack reference to the c-string I was trying to 
> keep alive.

At the risk of over-doing this, one more thing I want to say in 
the interest of clarity: the incorrect documentation led me right 
into this error: "This is accomplished by ..... Leaving a pointer 
to it on the stack (as a parameter or automatic variable), as the 
garbage collector will scan
the stack."

I've fixed my code using addRoot/removeRoot and so far it seems 
to work.