How to get nogc to work with manual memory allocation
Bienlein via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Sun Aug 24 01:03:09 PDT 2014
Hello,
I was having a look at the new nogc annotation and therefore
wrote some code that creates an instance on the heap bypassing
the GC (code adapted from http://dpaste.dzfl.pl/2377217c7870).
Problem is that calls to call the class' constructor, destructor
and others can't be called anymore once nogc is used. So the
question is how to get manual allocation and deallocation done
with using nogc. Here is the experimental code:
@nogc
T nogcNew(T, Args...) (Args args)
{
import std.conv : emplace;
import core.stdc.stdlib : malloc;
// get class size of class object in bytes
auto size = __traits(classInstanceSize, T);
// allocate memory for the object
auto memory = malloc(size)[0..size];
if(!memory)
{
import core.exception : onOutOfMemoryError;
onOutOfMemoryError();
}
// call T's constructor and emplace instance on
// newly allocated memory
return emplace!(T, Args)(memory, args);
}
@nogc
void nogcDel(T)(T obj)
{
import core.stdc.stdlib : free;
// calls obj's destructor
destroy(obj);
// free memory occupied by object
free(cast(void*)obj);
}
@nogc
void main()
{
TestClass test = nogcNew!TestClass();
test.x = 123;
nogcDel(test);
test.x = 456; // no protection violation ?!
// remove @nogc to run this
TestClass t = new TestClass();
t.x = 789;
delete t;
t.x = 678; // protection violation as expected
}
I have omitted the code for the TestClass class to save space.
Problem is that the compiler outputs this:
Error: @nogc function 'main.nogcNew!(TestClass, ).nogcNew' cannot
call non- at nogc function 'core.exception.onOutOfMemoryError'
Error: @nogc function 'main.nogcNew!(TestClass, ).nogcNew' cannot
call non- at nogc function 'std.conv.emplace!(TestClass, ).emplace'
Error: @nogc function 'main.nogcDel!(TestClass).nogcDel' cannot
call non- at nogc function 'object.destroy!(TestClass).destroy'
Is there a way to get around this? Then the test.x = 456; did not
cause a protection violation although the instance was
deallocated before calling nogcDel. Something with the
deallocation in nogcDel seems not to work. Some hint appreciated
on this. When calling delete t the protection violation happens
on the next line as expected.
Thanks a lot, Bienlein
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