On Monday, 5 June 2017 at 23:30:00 UTC, Stanislav Blinov wrote:
On Monday, 5 June 2017 at 13:11:25 UTC, Steven Schveighoffer
wrote:
adding a range marks it as having pointers to scan, AND stores
a reference to that array, so it won't be GC collected (nor
will anything it points to). The intention is for it to be
used on non-GC memory, like C malloc'd memory, where it
doesn't matter that the GC is pointing at it.
Huh?
https://dlang.org/phobos/core_memory.html#.GC.addRange :
Note that p[0 .. sz] is treated as an opaque range of memory
assumed to be suitably managed by the caller. In particular,
if p points into a GC-managed memory block, addRange does not
mark this block as live.
Is that paragraph wrong?
No I am wrong. I assumed that because the gc is part of the
static space it's metadata would also be scanned. But the data is
allocated using c malloc, so it's not scanned. This makes any
partial insertion using addrange more dangerous actually because
you have to take care to keep a pointer to that block somewhere
I would say that you are better off allocating 2 arrays -- one
with NO_SCAN where you put your non-pointer-containing data,
and one without the flag to put your other data. This is
similar to your "selective" function, but instead of
allocating 1 array, with a tuple of slices into it, just
allocate 2 arrays and return the tuple of those 2 arrays.
Then it's just the obvious() function. The whole point of the
exercise is to make one GC allocation instead of N :) But still
GC, so as not to put additional responsibility on the caller.
No, 2 allocations instead of N.
-Steve
