toStringz documentation is clear on why, when, and how to extend the
lifetime of a D string:
https://dlang.org/phobos/std_string.html#.toStringz
Assume foo is a D library function that passes a "string" result to e.g. C:
extern(C)
void foo(ref const(char) * name) {
name = format!"file%s.txt"(42).toStringz; // Allocates from GC memory
}
This may be fine for "immediate use" on the C side because at first
glance no garbage collection can take place between our returning the
result and their using it:
// C caller:
const char * name = NULL;
foo(&name); // Calls us
printf("%s", name); // Uses 'name' immediately
Is it really safe? Imagine a multi-threaded environment where another D
function is executed that triggers a GC collection right before the printf.
Does the GC see that local variable 'name' that is on the C side? What I
don't know is whether the GC is aware only of the stack frames of D
functions or the entire thread, which would include the C caller's 'name'.
Ali
