digitalmars.D.bugs - [Issue 429] New: Unable to distinguish between empty and uninitialized dynamic arrays
- d-bugmail puremagic.com (122/122) Oct 11 2006 http://d.puremagic.com/issues/show_bug.cgi?id=429
- Ameer Armaly (10/141) Oct 14 2006 Perhaps a better solution to this would be some sort of capacity variabl...
- d-bugmail puremagic.com (9/9) Oct 18 2006 http://d.puremagic.com/issues/show_bug.cgi?id=429
- d-bugmail puremagic.com (10/10) Nov 08 2006 http://d.puremagic.com/issues/show_bug.cgi?id=429
- d-bugmail puremagic.com (9/9) Nov 25 2006 http://d.puremagic.com/issues/show_bug.cgi?id=429
http://d.puremagic.com/issues/show_bug.cgi?id=429
Summary: Unable to distinguish between empty and uninitialized
dynamic arrays
Product: D
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: minor
Priority: P4
Component: Phobos
AssignedTo: bugzilla digitalmars.com
ReportedBy: ddparnell bigpond.com
When setting the length of a dynamic array to zero, phobos (gc) also frees the
RAM for that array. This means that applications cannot tell an uninitialized
array from an empty array. It also means that an application cannot reserve RAM
in the generic case.
Note that reducing the length of an array to a value greater than zero does not
cause this behaviour, instead all the RAM for the array is reusable when the
application later increases the length.
Example:
int[] test;
test.length = 10;
// Show address of array start and its length (10)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 1;
// Show address of array start and its length (1)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 8;
// Show address of array start and its length (8)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 0;
// Shows 0 and 0!
writefln("%s %s", cast(uint)test.ptr, test.length);
If an application needs to reset an array to the uninitialized state then it
can do 'arrayname = null;'.
The change to gc.d could be done as a two-line change ...
extern (C)
byte[] _d_arraysetlength2(size_t newlength, size_t sizeelem, Array *p, ...)
in
{
assert(sizeelem);
assert(!p.length || p.data);
}
body
{
byte* newdata;
debug(PRINTF)
{
printf("_d_arraysetlength2(p = %p, sizeelem = %d, newlength = %d)\n",
p, sizeelem, newlength);
if (p)
printf("\tp.data = %p, p.length = %d\n", p.data, p.length);
}
if (newlength)
{
version (D_InlineAsm_X86)
{
size_t newsize = void;
asm
{
mov EAX,newlength ;
mul EAX,sizeelem ;
mov newsize,EAX ;
jc Loverflow ;
}
}
else
{
size_t newsize = sizeelem * newlength;
if (newsize / newlength != sizeelem)
goto Loverflow;
}
//printf("newsize = %x, newlength = %x\n", newsize, newlength);
size_t size = p.length * sizeelem;
if (p.data) // <<-CHG
{
newdata = p.data;
if (newlength > p.length)
{
size_t cap = _gc.capacity(p.data);
if (cap <= newsize)
{
newdata = cast(byte *)_gc.malloc(newsize + 1);
newdata[0 .. size] = p.data[0 .. size];
}
}
}
else
{
newdata = cast(byte *)_gc.malloc(newsize + 1);
}
va_list q;
va_start!(Array *)(q, p); // q is pointer to initializer
if (newsize > size)
{
if (sizeelem == 1)
{
//printf("newdata = %p, size = %d, newsize = %d, *q = %d\n",
newdata, size, newsize, *cast(byte*)q);
newdata[size .. newsize] = *(cast(byte*)q);
}
else
{
for (size_t u = size; u < newsize; u += sizeelem)
{
memcpy(newdata + u, q, sizeelem);
}
}
}
}
else
{
newdata = p.data; //<<-CHG
}
p.data = newdata;
p.length = newlength;
return newdata[0 .. newlength];
Loverflow:
_d_OutOfMemory();
}
--
Oct 11 2006
"Ameer Armaly" <ameer_armaly hotmail.com>
<d-bugmail puremagic.com> wrote in message
news:bug-429-3 http.d.puremagic.com/issues/...
http://d.puremagic.com/issues/show_bug.cgi?id=429
Summary: Unable to distinguish between empty and uninitialized
dynamic arrays
Product: D
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: minor
Priority: P4
Component: Phobos
AssignedTo: bugzilla digitalmars.com
ReportedBy: ddparnell bigpond.com
When setting the length of a dynamic array to zero, phobos (gc) also frees
the
RAM for that array. This means that applications cannot tell an
uninitialized
array from an empty array. It also means that an application cannot
reserve RAM
in the generic case.
Note that reducing the length of an array to a value greater than zero
does not
cause this behaviour, instead all the RAM for the array is reusable when
the
application later increases the length.
Example:
int[] test;
test.length = 10;
// Show address of array start and its length (10)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 1;
// Show address of array start and its length (1)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 8;
// Show address of array start and its length (8)
writefln("%s %s", cast(uint)test.ptr, test.length);
test.length = 0;
// Shows 0 and 0!
writefln("%s %s", cast(uint)test.ptr, test.length);
If an application needs to reset an array to the uninitialized state then
it
can do 'arrayname = null;'.
The change to gc.d could be done as a two-line change ...
extern (C)
byte[] _d_arraysetlength2(size_t newlength, size_t sizeelem, Array *p,
...)
in
{
assert(sizeelem);
assert(!p.length || p.data);
}
body
{
byte* newdata;
debug(PRINTF)
{
printf("_d_arraysetlength2(p = %p, sizeelem = %d, newlength =
%d)\n",
p, sizeelem, newlength);
if (p)
printf("\tp.data = %p, p.length = %d\n", p.data, p.length);
}
if (newlength)
{
version (D_InlineAsm_X86)
{
size_t newsize = void;
asm
{
mov EAX,newlength ;
mul EAX,sizeelem ;
mov newsize,EAX ;
jc Loverflow ;
}
}
else
{
size_t newsize = sizeelem * newlength;
if (newsize / newlength != sizeelem)
goto Loverflow;
}
//printf("newsize = %x, newlength = %x\n", newsize, newlength);
size_t size = p.length * sizeelem;
if (p.data) // <<-CHG
{
newdata = p.data;
if (newlength > p.length)
{
size_t cap = _gc.capacity(p.data);
if (cap <= newsize)
{
newdata = cast(byte *)_gc.malloc(newsize + 1);
newdata[0 .. size] = p.data[0 .. size];
}
}
}
else
{
newdata = cast(byte *)_gc.malloc(newsize + 1);
}
va_list q;
va_start!(Array *)(q, p); // q is pointer to initializer
if (newsize > size)
{
if (sizeelem == 1)
{
//printf("newdata = %p, size = %d, newsize = %d, *q =
%d\n",
newdata, size, newsize, *cast(byte*)q);
newdata[size .. newsize] = *(cast(byte*)q);
}
else
{
for (size_t u = size; u < newsize; u += sizeelem)
{
memcpy(newdata + u, q, sizeelem);
}
}
}
}
else
{
newdata = p.data; //<<-CHG
}
p.data = newdata;
p.length = newlength;
return newdata[0 .. newlength];
Loverflow:
_d_OutOfMemory();
}
--
Perhaps a better solution to this would be some sort of capacity variable;
setting length to 0 does nothing, but setting capacity to 0 frees memmory.
Capacity would contain the maximum amount an array could hold without a new
allocation, and if length is set greater than capacity a new allocation
occurs and capacity is adjusted accordingly. This way the size of the
memmory block and the actual array are two different things if you wanted to
use them that way , but at the same time you can treat them as the same
thing.
Oct 14 2006
http://d.puremagic.com/issues/show_bug.cgi?id=429
bugzilla digitalmars.com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
Fixed DMD 0.170
--
Oct 18 2006
http://d.puremagic.com/issues/show_bug.cgi?id=429
mk krej.cz changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|FIXED |
Linux DMD 0.173 seems to still have the original issue, Windows version works
ok.
--
Nov 08 2006
http://d.puremagic.com/issues/show_bug.cgi?id=429
bugzilla digitalmars.com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |FIXED
Fixed DMD 0.175
--
Nov 25 2006