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fallback_allocator.d
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fallback_allocator.d
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// Written in the D programming language.
/**
Source: $(PHOBOSSRC std/experimental/allocator/building_blocks/fallback_allocator.d)
*/
module std.experimental.allocator.building_blocks.fallback_allocator;
import std.experimental.allocator.common;
/**
`FallbackAllocator` is the allocator equivalent of an "or" operator in
algebra. An allocation request is first attempted with the `Primary`
allocator. If that returns `null`, the request is forwarded to the $(D
Fallback) allocator. All other requests are dispatched appropriately to one of
the two allocators.
In order to work, `FallbackAllocator` requires that `Primary` defines the
`owns` method. This is needed in order to decide which allocator was
responsible for a given allocation.
`FallbackAllocator` is useful for fast, special-purpose allocators backed up
by general-purpose allocators. The example below features a stack region backed
up by the `GCAllocator`.
*/
struct FallbackAllocator(Primary, Fallback)
{
import std.algorithm.comparison : min;
import std.traits : hasMember;
import std.typecons : Ternary;
// Need both allocators to be stateless
// This is to avoid using default initialized stateful allocators
static if (!stateSize!Primary && !stateSize!Fallback)
version (StdUnittest)
@system unittest
{
testAllocator!(() => FallbackAllocator());
}
/// The primary allocator.
static if (stateSize!Primary) Primary primary;
else alias primary = Primary.instance;
/// The fallback allocator.
static if (stateSize!Fallback) Fallback fallback;
else alias fallback = Fallback.instance;
/**
If both `Primary` and `Fallback` are stateless, `FallbackAllocator`
defines a static instance called `instance`.
*/
static if (!stateSize!Primary && !stateSize!Fallback)
{
static FallbackAllocator instance;
}
/**
The alignment offered is the minimum of the two allocators' alignment.
*/
enum uint alignment = min(Primary.alignment, Fallback.alignment);
/**
Allocates memory trying the primary allocator first. If it returns $(D
null), the fallback allocator is tried.
*/
void[] allocate(size_t s)
{
auto result = primary.allocate(s);
return result.length == s ? result : fallback.allocate(s);
}
static if (hasMember!(Primary, "allocateZeroed")
|| (hasMember!(Fallback, "allocateZeroed")))
package(std) void[] allocateZeroed()(size_t s)
{
// Try to allocate with primary.
static if (hasMember!(Primary, "allocateZeroed"))
{
void[] result = primary.allocateZeroed(s);
if (result.length == s) return result;
}
else
{
void[] result = primary.allocate(s);
if (result.length == s)
{
(() @trusted => (cast(ubyte[]) result)[] = 0)();
return result;
}
}
// Allocate with fallback.
static if (hasMember!(Fallback, "allocateZeroed"))
{
return fallback.allocateZeroed(s);
}
else
{
result = fallback.allocate(s);
(() @trusted => (cast(ubyte[]) result)[] = 0)(); // OK even if result is null.
return result;
}
}
/**
`FallbackAllocator` offers `alignedAllocate` iff at least one of the
allocators also offers it. It attempts to allocate using either or both.
*/
static if (hasMember!(Primary, "alignedAllocate")
|| hasMember!(Fallback, "alignedAllocate"))
void[] alignedAllocate(size_t s, uint a)
{
static if (hasMember!(Primary, "alignedAllocate"))
{{
auto result = primary.alignedAllocate(s, a);
if (result.length == s) return result;
}}
static if (hasMember!(Fallback, "alignedAllocate"))
{{
auto result = fallback.alignedAllocate(s, a);
if (result.length == s) return result;
}}
return null;
}
/**
`expand` is defined if and only if at least one of the allocators
defines `expand`. It works as follows. If `primary.owns(b)`, then the
request is forwarded to `primary.expand` if it is defined, or fails
(returning `false`) otherwise. If `primary` does not own `b`, then
the request is forwarded to `fallback.expand` if it is defined, or fails
(returning `false`) otherwise.
*/
static if (hasMember!(Primary, "owns")
&& (hasMember!(Primary, "expand") || hasMember!(Fallback, "expand")))
bool expand(ref void[] b, size_t delta)
{
if (!delta) return true;
if (!b.ptr) return false;
if (primary.owns(b) == Ternary.yes)
{
static if (hasMember!(Primary, "expand"))
return primary.expand(b, delta);
else
return false;
}
static if (hasMember!(Fallback, "expand"))
return fallback.expand(b, delta);
else
return false;
}
/**
`reallocate` works as follows. If `primary.owns(b)`, then $(D
primary.reallocate(b, newSize)) is attempted. If it fails, an attempt is
made to move the allocation from `primary` to `fallback`.
If `primary` does not own `b`, then $(D fallback.reallocate(b,
newSize)) is attempted. If that fails, an attempt is made to move the
allocation from `fallback` to `primary`.
*/
static if (hasMember!(Primary, "owns"))
bool reallocate(ref void[] b, size_t newSize)
{
bool crossAllocatorMove(From, To)(ref From from, ref To to)
{
auto b1 = to.allocate(newSize);
if (b1.length != newSize) return false;
if (b.length < newSize) b1[0 .. b.length] = b[];
else b1[] = b[0 .. newSize];
static if (hasMember!(From, "deallocate"))
from.deallocate(b);
b = b1;
return true;
}
if (b is null || primary.owns(b) == Ternary.yes)
{
return primary.reallocate(b, newSize)
// Move from primary to fallback
|| crossAllocatorMove(primary, fallback);
}
return fallback.reallocate(b, newSize)
// Interesting. Move from fallback to primary.
|| crossAllocatorMove(fallback, primary);
}
static if (hasMember!(Primary, "owns")
&& (hasMember!(Primary, "alignedAllocate")
|| hasMember!(Fallback, "alignedAllocate")))
bool alignedReallocate(ref void[] b, size_t newSize, uint a)
{
bool crossAllocatorMove(From, To)(ref From from, ref To to)
{
static if (!hasMember!(To, "alignedAllocate"))
{
return false;
}
else
{
auto b1 = to.alignedAllocate(newSize, a);
if (b1.length != newSize) return false;
if (b.length < newSize) b1[0 .. b.length] = b[];
else b1[] = b[0 .. newSize];
static if (hasMember!(From, "deallocate"))
from.deallocate(b);
b = b1;
return true;
}
}
static if (hasMember!(Primary, "alignedAllocate"))
{
if (b is null || primary.owns(b) == Ternary.yes)
{
return primary.alignedReallocate(b, newSize, a)
|| crossAllocatorMove(primary, fallback);
}
}
static if (hasMember!(Fallback, "alignedAllocate"))
{
return fallback.alignedReallocate(b, newSize, a)
|| crossAllocatorMove(fallback, primary);
}
else
{
return false;
}
}
/**
`owns` is defined if and only if both allocators define `owns`.
Returns $(D primary.owns(b) | fallback.owns(b)).
*/
static if (hasMember!(Primary, "owns") && hasMember!(Fallback, "owns"))
Ternary owns(void[] b)
{
return primary.owns(b) | fallback.owns(b);
}
/**
`resolveInternalPointer` is defined if and only if both allocators
define it.
*/
static if (hasMember!(Primary, "resolveInternalPointer")
&& hasMember!(Fallback, "resolveInternalPointer"))
Ternary resolveInternalPointer(const void* p, ref void[] result)
{
Ternary r = primary.resolveInternalPointer(p, result);
return r == Ternary.no ? fallback.resolveInternalPointer(p, result) : r;
}
/**
`deallocate` is defined if and only if at least one of the allocators
define `deallocate`. It works as follows. If `primary.owns(b)`,
then the request is forwarded to `primary.deallocate` if it is defined,
or is a no-op otherwise. If `primary` does not own `b`, then the
request is forwarded to `fallback.deallocate` if it is defined, or is a
no-op otherwise.
*/
static if (hasMember!(Primary, "owns") &&
(hasMember!(Primary, "deallocate")
|| hasMember!(Fallback, "deallocate")))
bool deallocate(void[] b)
{
if (primary.owns(b) == Ternary.yes)
{
static if (hasMember!(Primary, "deallocate"))
return primary.deallocate(b);
else
return false;
}
else
{
static if (hasMember!(Fallback, "deallocate"))
return fallback.deallocate(b);
else
return false;
}
}
/**
`empty` is defined if both allocators also define it.
Returns: $(D primary.empty & fallback.empty)
*/
static if (hasMember!(Primary, "empty")
&& hasMember!(Fallback, "empty"))
Ternary empty()
{
return primary.empty & fallback.empty;
}
}
@system unittest
{
import std.conv : text;
import std.experimental.allocator.building_blocks.region : InSituRegion;
import std.experimental.allocator.gc_allocator : GCAllocator;
import std.typecons : Ternary;
FallbackAllocator!(InSituRegion!16_384, GCAllocator) a;
// This allocation uses the stack
auto b1 = a.allocate(1024);
assert(b1.length == 1024, text(b1.length));
assert((() pure nothrow @safe @nogc => a.primary.owns(b1))() == Ternary.yes);
assert((() nothrow => a.reallocate(b1, 2048))());
assert(b1.length == 2048, text(b1.length));
assert((() pure nothrow @safe @nogc => a.primary.owns(b1))() == Ternary.yes);
// This large allocation will go to the GCAllocator
auto b2 = a.allocate(1024 * 1024);
assert((() pure nothrow @safe @nogc => a.primary.owns(b2))() == Ternary.no);
// Ensure deallocate inherits from parent allocators
() nothrow @nogc { a.deallocate(b1); }();
() nothrow @nogc { a.deallocate(b2); }();
}
@system unittest
{
import std.experimental.allocator.building_blocks.bitmapped_block : BitmappedBlockWithInternalPointers;
import std.typecons : Ternary;
alias A =
FallbackAllocator!(
BitmappedBlockWithInternalPointers!(4096),
BitmappedBlockWithInternalPointers!(4096)
);
A a = A(
BitmappedBlockWithInternalPointers!(4096)(new ubyte[4096 * 1024]),
BitmappedBlockWithInternalPointers!(4096)(new ubyte[4096 * 1024])
);
assert((() nothrow @safe @nogc => a.empty)() == Ternary.yes);
auto b = a.allocate(201);
assert(b.length == 201);
assert(a.reallocate(b, 202));
assert(b.length == 202);
assert((() nothrow @safe @nogc => a.empty)() == Ternary.no);
}
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.typecons : Ternary;
auto a = FallbackAllocator!(Region!(), Region!())(
Region!()(new ubyte[4096 * 1024]),
Region!()(new ubyte[4096 * 1024]));
auto b = a.alignedAllocate(42, 8);
assert(b.length == 42);
assert((() nothrow @nogc => a.alignedReallocate(b, 100, 8))());
assert(b.length == 100);
}
version (StdUnittest)
@system unittest
{
import std.experimental.allocator.building_blocks.bitmapped_block : BitmappedBlockWithInternalPointers;
import std.typecons : Ternary;
alias A =
FallbackAllocator!(
BitmappedBlockWithInternalPointers!(4096),
BitmappedBlockWithInternalPointers!(4096)
);
// Run testAllocator here since both allocators stateful
testAllocator!(
() => A(
BitmappedBlockWithInternalPointers!(4096)(new ubyte[4096 * 1024]),
BitmappedBlockWithInternalPointers!(4096)(new ubyte[4096 * 1024])
)
);
}
@system unittest
{
import std.experimental.allocator.mallocator : Mallocator;
import std.typecons : Ternary;
alias a = FallbackAllocator!(Mallocator, Mallocator).instance;
auto b = a.allocate(42);
assert(b.length == 42);
assert((() nothrow @nogc => a.reallocate(b, 100))());
assert(b.length == 100);
}
/*
Forwards an argument from one function to another
*/
private auto ref forward(alias arg)()
{
static if (__traits(isRef, arg))
{
return arg;
}
else
{
import std.algorithm.mutation : move;
return move(arg);
}
}
@safe unittest
{
void fun(T)(auto ref T, string) { /* ... */ }
void gun(T...)(auto ref T args)
{
fun(forward!(args[0]), forward!(args[1]));
}
gun(42, "hello");
int x;
gun(x, "hello");
}
@safe unittest
{
static void checkByRef(T)(auto ref T value)
{
static assert(__traits(isRef, value));
}
static void checkByVal(T)(auto ref T value)
{
static assert(!__traits(isRef, value));
}
static void test1(ref int a) { checkByRef(forward!a); }
static void test2(int a) { checkByVal(forward!a); }
static void test3() { int a; checkByVal(forward!a); }
}
/**
Convenience function that uses type deduction to return the appropriate
`FallbackAllocator` instance. To initialize with allocators that don't have
state, use their `it` static member.
*/
FallbackAllocator!(Primary, Fallback)
fallbackAllocator(Primary, Fallback)(auto ref Primary p, auto ref Fallback f)
{
alias R = FallbackAllocator!(Primary, Fallback);
static if (stateSize!Primary)
static if (stateSize!Fallback)
return R(forward!p, forward!f);
else
return R(forward!p);
else
static if (stateSize!Fallback)
return R(forward!f);
else
return R();
}
///
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.gc_allocator : GCAllocator;
import std.typecons : Ternary;
auto a = fallbackAllocator(Region!GCAllocator(1024), GCAllocator.instance);
auto b1 = a.allocate(1020);
assert(b1.length == 1020);
assert(a.primary.owns(b1) == Ternary.yes);
auto b2 = a.allocate(10);
assert(b2.length == 10);
assert(a.primary.owns(b2) == Ternary.no);
}
version (StdUnittest)
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.experimental.allocator.gc_allocator : GCAllocator;
testAllocator!(() => fallbackAllocator(Region!GCAllocator(1024), GCAllocator.instance));
}
// Ensure `owns` inherits function attributes
@system unittest
{
import std.experimental.allocator.building_blocks.region : InSituRegion;
import std.typecons : Ternary;
FallbackAllocator!(InSituRegion!16_384, InSituRegion!16_384) a;
auto buff = a.allocate(42);
assert((() pure nothrow @safe @nogc => a.owns(buff))() == Ternary.yes);
}
@system unittest
{
import std.experimental.allocator.gc_allocator : GCAllocator;
import std.typecons : Ternary;
auto a = fallbackAllocator(GCAllocator.instance, GCAllocator.instance);
auto b = a.allocate(1020);
assert(b.length == 1020);
void[] p;
assert((() nothrow @safe @nogc => a.resolveInternalPointer(null, p))() == Ternary.no);
assert((() nothrow @safe @nogc => a.resolveInternalPointer(&b[0], p))() == Ternary.yes);
}
@system unittest
{
import std.experimental.allocator.building_blocks.region : Region;
import std.typecons : Ternary;
alias A = FallbackAllocator!(Region!(), Region!());
auto a = A(Region!()(new ubyte[16_384]), Region!()(new ubyte[16_384]));
auto b = a.allocate(42);
assert(b.length == 42);
assert((() pure nothrow @safe @nogc => a.owns(b))() == Ternary.yes);
assert((() nothrow @safe @nogc => a.expand(b, 58))());
assert(b.length == 100);
}