On Sunday, 30 May 2021 at 17:31:37 UTC, Dukc wrote:
On Sunday, 30 May 2021 at 14:28:25 UTC, Dylan Graham wrote:
Hi, all!
This is LWDR (Light Weight D Runtime) It is a ground-up
implementation of a D runtime targeting the ARM Cortex-M
microcontrollers and other microcontroller platforms with
RTOSes (Real Time Operating Systems).
Sounds very useful! However, first thing first: What's the
license? DUB package says it's FOSS. Great, but what kind of
FOSS? It makes a big difference whether it's GNU or BSD, for
instance.
I haven't put any thought into the license. Since LWDR is derived
from DRuntime, I assume I'll have to use its license. If not, I'd
like to go with something permissive like MIT.
It doesn't, and possibly may not, support all D features in
order to make it viable for the constrained environments. For
example, all memory allocation is manually done via `new` and
`delete` - no GC.
Regarding `new` - is there a good way to iterate though chunks
allocated with `new`? One could call an unmodified piece of D
code that normally uses the GC, and then manually free all it's
allocations.
Bingo. I was thinking of thread-local tracking of allocations.
Something like follows:
Impl:
```D
size_t numAllocations = 0;
List!(void*) allocations;
void* allocateMemoryForNew(int size)
{
numAllocations++;
auto ptr = rtosbackend_heapalloc(size);
allocations.add(ptr);
return allocations;
}
void deallocateMemory(void* ptr)
{
allocations.removeLastOccurenceOf(ptr);
numAllocations--;
rtosbackend_heapfreealloc(ptr);
}
struct MemAlloc
{
size_t allocs;
void free() {
// allocs should be less than numAllocations,
// so delete the last n items of allocations
auto difference = numAllocations - allocs;
foreach(i; 0 .. difference) {
auto ptr = allocations[allocations.length - i];
// get ith to last
deallocateMemory(ptr);
}
}
}
MemAlloc enterTrackedMemory()
{
return MemAlloc(.numAllocations);
}
```
Usage:
```D
auto mem0 = enterTrackedMemory(); // mem0 says that there should
be 0 allocations
A a = new A(); // 1 allocation
{
auto mem1 = enterTrackedMemory(); // mem1 says that there
should be 1 allocations total
auto b = new A(); // 1 allocation, so total is now 2
mem1.free; // we need to get back to 1 allocation, so delete
b (most recent allocation)
}
mem0.free; // delete everything
```
This works with `scope(...)`.
There's some caveats with this - if a phobos function calls a
user function, anything that user function allocates will be
wiped, too (may or may not be desirable behaviour), unless some
protocol for opting out of tracking is implemented.
It works by providing a series of barebones API hooks (alloc,
dealloc, assert, etc) (defined in `rtoslink.d`), which you
must implement and/or point to your RTOS implementation.
Quickly looking, the implementation looks very portable, save
for exceptions. with `rtoslink.d`, this will probably enable a
lot of stuff on any platform without DRuntime. Not just
microcontrollers. If I'm right, you just did a BIG service for
D on bare-metal.
Exceptions are a nightmare. It works for GDC with GCC code. My
codebase uses GCC for its C (ST toolchain), so I need to write
some code that can take LDC's exception handling and make it
compatible with how GCC operates. So, it looks like there will be
multiple exception handling implementations (LDC with GCC
backend, LDC with clang backend, GDC with GCC backend). I wish D
had something like Zig's error handling.
Otherwise, thank you! It was designed to be agnostic as much as
possible. I didn't know it'd help out for more than just
microcontrollers :)
