On Monday, 22 December 2014 at 16:51:30 UTC, Allocator stack
wrote:
How about allocators stack? Allocator e.g. one of these
https://github.com/andralex/phobos/blob/allocator/std/allocator.d
-------------
allocatorStack.push(new GCAllocator);
//Some code that use memory allocation
auto a = ['x', 'y'];
a ~= ['a', 'b']; // use allocatorStack.top.realloc(...);
allocatorStack.pop();
-------------
Allocators must be equipped with dynamic polymorphism. For those
cases when it is too expensive attribute
@allocator(yourAllocator) applied to declaration set allocator
statically.
-------------
@allocator(Mallocator.instance)
void f()
{
// Implicitly use global(tls?) allocator Mallocator when
allocate an
object or resize an array or etc.
}
@allocator("StackAllocator")
void f()
{
// Implicitly use allocatorStack.top() allocator when allocate
an
object or resize an array or etc.
}
-------------
There is some issues to solve. E.g. how to eliminate mix memory
from different allocators.
I've put together some semi-realistic code that touches on this
(ignore the `scope` thingies in there):
http://wiki.dlang.org/User:Schuetzm/RC,_Owned_and_allocators
The goal was to allow returning owned objects from functions that
don't know what kind of memory management strategy the end user
wants to use. The caller can then decide to convert them into ref
counted objects, or release them and let the GC take care of
them, or just use them in a UFCS chain and let them get destroyed
at the end of the current statement automatically.
This is achieved by storing a pointer to the allocator (which is
an interface) next to the object. (As a side note, these
interfaces can be auto-implemented by templates when needed,
similar to `std.range.InputRange` et al.)
This design makes it possible to switch allocators at runtime in
any order, either through a global variable, or by passing a
parameter to a function. It also avoids template bloat, because
the functions involved just need to return Owned!MyType, which
does not depend on the allocator type. The downside is, of
course, the overhead of the indirect calls. (The call to
`reallocate` can be left out in this example if `Owned` already
preallocates some space for the refcount, therefore it's just two
indirect calls for the lifetime of a typical object: one each for
creation and destruction.)
As for static allocators, I think it's not possible without
sacrificing the ability to switch allocators at runtime and
without templating on the allocator.
