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module dparse.rollback_allocator;
import core.memory : GC;
//version = debug_rollback_allocator;
/**
* Pointer-bump allocator with rollback functionality.
*/
struct RollbackAllocator
{
public:
// must be multiple of 8
enum memoryAlignment = 16u;
@disable this(this);
~this()
{
while (first !is null)
deallocateNode();
}
/**
* Allocates `size` bytes of memory.
*/
void[] allocate(const size_t size)
out (arr)
{
assert(arr.length == size);
}
do
{
import std.algorithm.comparison : min;
if (first is null)
allocateNode(size);
// Memory align the size
immutable size_t s = size & ~(cast(size_t) memoryAlignment - 1);
immutable size_t s2 = s == size ? size : s + memoryAlignment;
size_t fu = first.used;
size_t end = fu + s2;
//assert(end >= fu + size);
//assert(end % 8 == 0);
if (end > first.mem.length)
{
allocateNode(size);
fu = first.used;
end = fu + s2;
}
//assert((cast(size_t) first.mem.ptr) % 8 == 0);
//assert(((cast(size_t) first.mem.ptr) + end) % 8 == 0);
void[] m = first.mem[fu .. fu + size];
// alignment can make our size here bigger than what we actually have, so we clamp down to the used amount
first.used = min(end, first.mem.length);
return m;
}
/**
* Rolls back the allocator to the given checkpoint.
*/
void rollback(size_t point)
{
import std.stdio : stderr;
if (point == 0)
{
while (first)
deallocateNode();
return;
}
else
assert(contains(point), "Attepmted to roll back to a point not in the allocator.");
// while `first !is null` is always going to pass after the contains(point) check, it may no longer pass after deallocateNode
while (first !is null && !first.contains(point))
deallocateNode();
assert(first !is null);
immutable begin = point - cast(size_t) first.mem.ptr;
version (debug_rollback_allocator)
(cast(ubyte[]) first.mem)[begin .. $] = 0;
first.used = begin;
assert(cast(size_t) first.mem.ptr + first.used == point);
}
/**
* Get a checkpoint for the allocator.
*/
size_t setCheckpoint() const nothrow @nogc
{
assert(first is null || first.used <= first.mem.length);
return first is null ? 0 : cast(size_t) first.mem.ptr + first.used;
}
/**
* Allocates a T and returns a pointer to it
*/
auto make(T, Args...)(auto ref Args args)
{
import std.algorithm.comparison : max;
import std.experimental.allocator : stateSize;
import std.conv : emplace;
void[] mem = allocate(max(stateSize!T, 1));
if (mem.ptr is null)
return null;
static if (is(T == class))
return emplace!T(mem, args);
else
return emplace(cast(T*) mem.ptr, args);
}
private:
// Used for debugging
bool contains(size_t point) const
{
for (const(Node)* n = first; n !is null; n = n.next)
if (n.contains(point))
return true;
return false;
}
static struct Node
{
Node* next;
size_t used;
ubyte[] mem;
bool contains(size_t p) const pure nothrow @nogc @safe
{
return p >= cast(size_t) mem.ptr && p <= cast(size_t) mem.ptr + mem.length;
}
}
void allocateNode(size_t size)
{
import core.exception : onOutOfMemoryError;
import std.algorithm : max;
import std.conv : emplace;
import std.experimental.allocator.mallocator : AlignedMallocator;
enum ALLOC_SIZE = 1024 * 8;
ubyte[] m = cast(ubyte[]) AlignedMallocator.instance.alignedAllocate(max(size + Node.sizeof, ALLOC_SIZE), memoryAlignment);
if (m is null)
onOutOfMemoryError();
GC.addRange(m.ptr, m.length);
version (debug_rollback_allocator)
m[] = 0;
Node* n = emplace!Node(cast(Node*) m.ptr, first, 0, m[Node.sizeof .. $]);
assert((cast(size_t) n.mem.ptr) % 8 == 0, "The memoriez!");
first = n;
}
void deallocateNode()
{
assert(first !is null);
import std.experimental.allocator.mallocator : AlignedMallocator;
Node* next = first.next;
ubyte[] mem = (cast(ubyte*) first)[0 .. Node.sizeof + first.mem.length];
version (debug_rollback_allocator)
mem[] = 0;
GC.removeRange(mem.ptr);
AlignedMallocator.instance.deallocate(mem);
first = next;
}
Node* first;
}
@("most simple usage, including memory across multiple pointers")
unittest
{
RollbackAllocator rba;
size_t[10] checkpoint;
foreach (i; 0 .. 10)
{
checkpoint[i] = rba.setCheckpoint();
rba.allocate(4000);
}
foreach_reverse (i; 0 .. 10)
{
rba.rollback(checkpoint[i]);
}
}
@("many allocates and frees while leaking memory")
unittest
{
RollbackAllocator rba;
foreach (i; 0 .. 10)
{
size_t[3] checkpoint;
foreach (n; 0 .. 3)
{
checkpoint[n] = rba.setCheckpoint();
rba.allocate(4000);
}
foreach_reverse (n; 1 .. 3)
{
rba.rollback(checkpoint[n]);
}
}
}
@("allocating overly big")
unittest
{
import std.stdio : stderr;
RollbackAllocator rba;
size_t[200] checkpoint;
size_t cp;
foreach (i; 1024 * 8 - 100 .. 1024 * 8 + 100)
{
try
{
checkpoint[cp++] = rba.setCheckpoint();
rba.allocate(i);
}
catch (Error e)
{
stderr.writeln("Unittest: crashed in allocating ", i, " bytes");
throw e;
}
}
foreach_reverse (i, c; checkpoint[0 .. cp])
{
try
{
rba.rollback(c);
}
catch (Error e)
{
stderr.writeln("Unittest: crashed in rolling back ", i, " (address ", c, ")");
throw e;
}
}
}