On Wednesday, 2 April 2014 at 16:51:57 UTC, Benjamin Thaut wrote:
Am 02.04.2014 17:57, schrieb Andrea Fontana:
I mean: if it is an exported function (of a shared library)
what
happens? There's no reference kept anywhere (in D). So if I'm
right it
could be freed immediatly by GC. Right?
If you pass that string to a C function, there is a reference
on the stack. So this string will not be freed until that
C-function returns. If that C-Function returns, it is very
likely however that this was the only reference and the string
will be freed the next time the garbage collector runs.
This is unfortunately only true on x86 32-bit. For x86_64, the
calling conventions (MS, SysV [1]) say that the first few
parameters are passed in registers, and the same is probably true
for other architectures.
Usually this is still safe, as the pointer will normally either
stay in its register, or will be spilled to the stack and kept
there as long as the function still needs to use it. But one
might imagine a corner case where it temporarily stores the
pointer in a global or static variable. Even if the pointer will
not be kept by the C function longer than the call, in such cases
you would need to keep an additional reference where the GC can
see it.
[1]
https://en.wikipedia.org/wiki/X86_calling_conventions#x86-64_calling_conventions
