libphobos/src/std/experimental/allocator/building_blocks/quantizer.d - gcc - Git at Google

 // Written in the D programming language.
 /**
 Source: $(PHOBOSSRC std/experimental/allocator/building_blocks/quantizer.d)
 */
 module std.experimental.allocator.building_blocks.quantizer;

 import std.experimental.allocator.common;

 /**
 This allocator sits on top of `ParentAllocator` and quantizes allocation sizes,
 usually from arbitrary positive numbers to a small set of round numbers (e.g.
 powers of two, page sizes etc). This technique is commonly used to:

 $(UL
 $(LI Preallocate more memory than requested such that later on, when
 reallocation is needed (e.g. to grow an array), expansion can be done quickly
 in place. Reallocation to smaller sizes is also fast (in-place) when the new
 size requested is within the same quantum as the existing size. Code that's
 reallocation-heavy can therefore benefit from fronting a generic allocator with
 a `Quantizer`. These advantages are present even if `ParentAllocator` does not
 support reallocation at all.)
 $(LI Improve behavior of allocators sensitive to allocation sizes, such as
 `FreeList` and `FreeTree`. Rounding allocation requests up makes for smaller
 free lists/trees at the cost of slack memory (internal fragmentation).)
 )

 The following methods are forwarded to the parent allocator if present:
 `allocateAll`, `owns`, `deallocateAll`, `empty`.

 Preconditions: `roundingFunction` must satisfy three constraints. These are
 not enforced (save for the use of `assert`) for the sake of efficiency.
 $(OL
 $(LI $(D roundingFunction(n) >= n) for all `n` of type `size_t`;)
 $(LI `roundingFunction` must be monotonically increasing, i.e. $(D
 roundingFunction(n1) <= roundingFunction(n2)) for all $(D n1 < n2);)
 $(LI `roundingFunction` must be `nothrow`, `@safe`, `@nogc` and `pure`, i.e.
 always return the same value for a given `n`.)
 )
 */
 struct Quantizer(ParentAllocator, alias roundingFunction)
 {
     import std.traits : hasMember;

     /**
     The parent allocator. Depending on whether `ParentAllocator` holds state
     or not, this is a member variable or an alias for
     `ParentAllocator.instance`.
     */
     static if (stateSize!ParentAllocator)
     {
         ParentAllocator parent;
     }
     else
     {
         alias parent = ParentAllocator.instance;
         __gshared Quantizer instance;
     }

     /**
     Returns `roundingFunction(n)`.
     */
     size_t goodAllocSize(size_t n)
     {
         auto result = roundingFunction(n);
         assert(result >= n);
         return result;
     }

     /**
     Alignment is identical to that of the parent.
     */
     enum alignment = ParentAllocator.alignment;

     /**
     Gets a larger buffer `buf` by calling
     `parent.allocate(goodAllocSize(n))`. If `buf` is `null`, returns
     `null`. Otherwise, returns $(D buf[0 .. n]).
     */
     void[] allocate(size_t n)
     {
         auto result = parent.allocate(goodAllocSize(n));
         return result.ptr ? result.ptr[0 .. n] : null;
     }

     static if (hasMember!(ParentAllocator, "allocateZeroed"))
     package(std) void[] allocateZeroed()(size_t n)
     {
         auto result = parent.allocateZeroed(goodAllocSize(n));
         return result.ptr ? result.ptr[0 .. n] : null;
     }

     /**
     Defined only if `parent.alignedAllocate` exists and works similarly to
     `allocate` by forwarding to
     $(D parent.alignedAllocate(goodAllocSize(n), a)).
     */
     static if (hasMember!(ParentAllocator, "alignedAllocate"))
     void[] alignedAllocate(size_t n, uint a)
     {
         auto result = parent.alignedAllocate(goodAllocSize(n), a);
         return result.ptr ? result.ptr[0 .. n] : null;
     }

     /**
     First checks whether there's enough slack memory preallocated for `b`
     by evaluating $(D b.length + delta <= goodAllocSize(b.length)). If that's
     the case, expands `b` in place. Otherwise, attempts to use
     `parent.expand` appropriately if present.
     */
     bool expand(ref void[] b, size_t delta)
     {
         if (!b || delta == 0) return delta == 0;
         immutable allocated = goodAllocSize(b.length),
             needed = b.length + delta,
             neededAllocation = goodAllocSize(needed);
         assert(b.length <= allocated);
         assert(needed <= neededAllocation);
         assert(allocated <= neededAllocation);
         // Second test needed because expand must work for null pointers, too.
         if (allocated == neededAllocation)
         {
             // Nice!
             b = (() @trusted => b.ptr[0 .. needed])();
             return true;
         }
         // Hail Mary
         static if (hasMember!(ParentAllocator, "expand"))
         {
             // Expand to the appropriate quantum
             auto original = (() @trusted => b.ptr[0 .. allocated])();
             assert(goodAllocSize(needed) >= allocated);
             if (!parent.expand(original, neededAllocation - allocated))
                 return false;
             // Dial back the size
             b = (() @trusted => original.ptr[0 .. needed])();
             return true;
         }
         else
         {
             return false;
         }
     }

     /**
     Expands or shrinks allocated block to an allocated size of $(D
     goodAllocSize(s)). Expansion occurs in place under the conditions required
     by `expand`. Shrinking occurs in place if $(D goodAllocSize(b.length)
     == goodAllocSize(s)).
     */
     bool reallocate(ref void[] b, size_t s)
     {
         if (!b.ptr)
         {
             b = allocate(s);
             return b.length == s;
         }
         if (s >= b.length && expand(b, s - b.length)) return true;
         immutable toAllocate = goodAllocSize(s),
             allocated = goodAllocSize(b.length);
         // Are the lengths within the same quantum?
         if (allocated == toAllocate)
         {
             // Reallocation (whether up or down) will be done in place
             b = b.ptr[0 .. s];
             return true;
         }
         // Defer to parent (or global) with quantized size
         auto original = b.ptr[0 .. allocated];
         if (!parent.reallocate(original, toAllocate)) return false;
         b = original.ptr[0 .. s];
         return true;
     }

     /**
     Defined only if `ParentAllocator.alignedAllocate` exists. Expansion
     occurs in place under the conditions required by `expand`. Shrinking
     occurs in place if $(D goodAllocSize(b.length) == goodAllocSize(s)).
     */
     static if (hasMember!(ParentAllocator, "alignedAllocate"))
     bool alignedReallocate(ref void[] b, size_t s, uint a)
     {
         if (!b.ptr)
         {
             b = alignedAllocate(s, a);
             return b.length == s;
         }
         if (s >= b.length && b.ptr.alignedAt(a) && expand(b, s - b.length)) return true;
         immutable toAllocate = goodAllocSize(s),
             allocated = goodAllocSize(b.length);
         // Are the lengths within the same quantum?
         if (allocated == toAllocate && b.ptr.alignedAt(a))
         {
             assert(b.ptr); // code above must have caught this
             // Reallocation (whether up or down) will be done in place
             b = b.ptr[0 .. s];
             return true;
         }
         // Defer to parent (or global) with quantized size
         auto original = b.ptr[0 .. allocated];
         if (!parent.alignedReallocate(original, toAllocate, a)) return false;
         b = original.ptr[0 .. s];
         return true;
     }

     /**
     Defined if `ParentAllocator.deallocate` exists and forwards to
     $(D parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)])).
     */
     static if (hasMember!(ParentAllocator, "deallocate"))
     bool deallocate(void[] b)
     {
         if (!b.ptr) return true;
         return parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)]);
     }

     // Forwarding methods
     mixin(forwardToMember("parent",
         "allocateAll", "owns", "deallocateAll", "empty"));
 }

 ///
 @system unittest
 {
     import std.experimental.allocator.building_blocks.free_tree : FreeTree;
     import std.experimental.allocator.gc_allocator : GCAllocator;

     size_t roundUpToMultipleOf(size_t s, uint base)
     {
         auto rem = s % base;
         return rem ? s + base - rem : s;
     }

     // Quantize small allocations to a multiple of cache line, large ones to a
     // multiple of page size
     alias MyAlloc = Quantizer!(
         FreeTree!GCAllocator,
         n => roundUpToMultipleOf(n, n <= 16_384 ? 64 : 4096));
     MyAlloc alloc;
     const buf = alloc.allocate(256);
     assert(buf.ptr);
 }

 version (StdUnittest)
 @system unittest
 {
     import std.experimental.allocator.gc_allocator : GCAllocator;
     alias MyAlloc = Quantizer!(GCAllocator,
         (size_t n) => n.roundUpToMultipleOf(64));
     testAllocator!(() => MyAlloc());

     assert((() pure nothrow @safe @nogc => MyAlloc().goodAllocSize(1))() == 64);

     auto a = MyAlloc();
     auto b = a.allocate(42);
     assert(b.length == 42);
     // Inplace expand, since goodAllocSize is 64
     assert((() @safe => a.expand(b, 22))());
     //assert((() nothrow @safe => a.expand(b, 22))());
     assert(b.length == 64);
     // Trigger parent.expand, which may or may not succed
     //() nothrow @safe { a.expand(b, 1); }();
     () @safe { a.expand(b, 1); }();
     assert(a.reallocate(b, 100));
     assert(b.length == 100);
     // Ensure deallocate inherits from parent
     () nothrow @nogc { a.deallocate(b); }();
 }

 @system unittest
 {
     import std.experimental.allocator.building_blocks.region : Region;
     import std.experimental.allocator.mallocator : Mallocator;
     import std.typecons : Ternary;

     alias Alloc = Quantizer!(Region!(Mallocator),
             (size_t n) => n.roundUpToMultipleOf(64));
     auto a = Alloc(Region!Mallocator(1024 * 64));
     const b = a.allocate(42);
     assert(b.length == 42);
     // Check that owns inherits from parent, i.e. Region
     assert((() pure nothrow @safe @nogc => a.owns(b))() == Ternary.yes);
     assert((() pure nothrow @safe @nogc => a.owns(null))() == Ternary.no);

     auto c = a.allocate(42);
     assert(c.length == 42);
     assert((() pure nothrow @safe @nogc => a.owns(c))() == Ternary.yes);
     // Inplace expand, since goodAllocSize is 64
     assert((() nothrow @safe => a.expand(c, 22))());
     assert(c.length == 64);
     // Trigger parent.expand
     assert((() nothrow @safe => a.expand(c, 1))());
     assert(c.length == 65);
     // Check that reallocate inherits from parent
     assert((() nothrow @nogc => a.reallocate(c, 100))());
     assert(c.length == 100);
 }

 version (StdUnittest)
 @system unittest
 {
     import std.experimental.allocator.building_blocks.region : Region;
     import std.experimental.allocator.mallocator : Mallocator;

     alias MyAlloc = Quantizer!(Region!(Mallocator),
             (size_t n) => n.roundUpToMultipleOf(64));
     testAllocator!(() => MyAlloc(Region!Mallocator(1024 * 64)));

     auto a = MyAlloc(Region!Mallocator(1024 * 64));
     void[] b;
     assert((() nothrow @nogc => a.alignedReallocate(b, 42, 16))());
     assert(b.length == 42);
     assert(alignedAt(&b[0], 16));
 }

 version (StdUnittest)
 @system unittest
 {
     import std.experimental.allocator.building_blocks.region : BorrowedRegion;
     import std.typecons : Ternary;

     alias MyAlloc = Quantizer!(BorrowedRegion!(),
         (size_t n) => n.roundUpToMultipleOf(64));
     testAllocator!(() => MyAlloc(BorrowedRegion!()(new ubyte[1024 * 64])));

     auto a = MyAlloc(BorrowedRegion!()(new ubyte[1024 * 64]));
     // Check that empty inherits from parent
     assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
     auto b = a.allocate(42);
     assert(b.length == 42);
     assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.no);
     // Check that deallocateAll inherits from parent
     assert((() nothrow @nogc => a.deallocateAll())());
     assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
 }
	// Written in the D programming language.
	/**
	Source: $(PHOBOSSRC std/experimental/allocator/building_blocks/quantizer.d)
	*/
	module std.experimental.allocator.building_blocks.quantizer;

	import std.experimental.allocator.common;

	/**
	This allocator sits on top of `ParentAllocator` and quantizes allocation sizes,
	usually from arbitrary positive numbers to a small set of round numbers (e.g.
	powers of two, page sizes etc). This technique is commonly used to:

	$(UL
	$(LI Preallocate more memory than requested such that later on, when
	reallocation is needed (e.g. to grow an array), expansion can be done quickly
	in place. Reallocation to smaller sizes is also fast (in-place) when the new
	size requested is within the same quantum as the existing size. Code that's
	reallocation-heavy can therefore benefit from fronting a generic allocator with
	a `Quantizer`. These advantages are present even if `ParentAllocator` does not
	support reallocation at all.)
	$(LI Improve behavior of allocators sensitive to allocation sizes, such as
	`FreeList` and `FreeTree`. Rounding allocation requests up makes for smaller
	free lists/trees at the cost of slack memory (internal fragmentation).)
	)

	The following methods are forwarded to the parent allocator if present:
	`allocateAll`, `owns`, `deallocateAll`, `empty`.

	Preconditions: `roundingFunction` must satisfy three constraints. These are
	not enforced (save for the use of `assert`) for the sake of efficiency.
	$(OL
	$(LI $(D roundingFunction(n) >= n) for all `n` of type `size_t`;)
	$(LI `roundingFunction` must be monotonically increasing, i.e. $(D
	roundingFunction(n1) <= roundingFunction(n2)) for all $(D n1 < n2);)
	$(LI `roundingFunction` must be `nothrow`, `@safe`, `@nogc` and `pure`, i.e.
	always return the same value for a given `n`.)
	)
	*/
	struct Quantizer(ParentAllocator, alias roundingFunction)
	{
	import std.traits : hasMember;

	/**
	The parent allocator. Depending on whether `ParentAllocator` holds state
	or not, this is a member variable or an alias for
	`ParentAllocator.instance`.
	*/
	static if (stateSize!ParentAllocator)
	{
	ParentAllocator parent;
	}
	else
	{
	alias parent = ParentAllocator.instance;
	__gshared Quantizer instance;
	}

	/**
	Returns `roundingFunction(n)`.
	*/
	size_t goodAllocSize(size_t n)
	{
	auto result = roundingFunction(n);
	assert(result >= n);
	return result;
	}

	/**
	Alignment is identical to that of the parent.
	*/
	enum alignment = ParentAllocator.alignment;

	/**
	Gets a larger buffer `buf` by calling
	`parent.allocate(goodAllocSize(n))`. If `buf` is `null`, returns
	`null`. Otherwise, returns $(D buf[0 .. n]).
	*/
	void[] allocate(size_t n)
	{
	auto result = parent.allocate(goodAllocSize(n));
	return result.ptr ? result.ptr[0 .. n] : null;
	}

	static if (hasMember!(ParentAllocator, "allocateZeroed"))
	package(std) void[] allocateZeroed()(size_t n)
	{
	auto result = parent.allocateZeroed(goodAllocSize(n));
	return result.ptr ? result.ptr[0 .. n] : null;
	}

	/**
	Defined only if `parent.alignedAllocate` exists and works similarly to
	`allocate` by forwarding to
	$(D parent.alignedAllocate(goodAllocSize(n), a)).
	*/
	static if (hasMember!(ParentAllocator, "alignedAllocate"))
	void[] alignedAllocate(size_t n, uint a)
	{
	auto result = parent.alignedAllocate(goodAllocSize(n), a);
	return result.ptr ? result.ptr[0 .. n] : null;
	}

	/**
	First checks whether there's enough slack memory preallocated for `b`
	by evaluating $(D b.length + delta <= goodAllocSize(b.length)). If that's
	the case, expands `b` in place. Otherwise, attempts to use
	`parent.expand` appropriately if present.
	*/
	bool expand(ref void[] b, size_t delta)
	{
	if (!b \|\| delta == 0) return delta == 0;
	immutable allocated = goodAllocSize(b.length),
	needed = b.length + delta,
	neededAllocation = goodAllocSize(needed);
	assert(b.length <= allocated);
	assert(needed <= neededAllocation);
	assert(allocated <= neededAllocation);
	// Second test needed because expand must work for null pointers, too.
	if (allocated == neededAllocation)
	{
	// Nice!
	b = (() @trusted => b.ptr[0 .. needed])();
	return true;
	}
	// Hail Mary
	static if (hasMember!(ParentAllocator, "expand"))
	{
	// Expand to the appropriate quantum
	auto original = (() @trusted => b.ptr[0 .. allocated])();
	assert(goodAllocSize(needed) >= allocated);
	if (!parent.expand(original, neededAllocation - allocated))
	return false;
	// Dial back the size
	b = (() @trusted => original.ptr[0 .. needed])();
	return true;
	}
	else
	{
	return false;
	}
	}

	/**
	Expands or shrinks allocated block to an allocated size of $(D
	goodAllocSize(s)). Expansion occurs in place under the conditions required
	by `expand`. Shrinking occurs in place if $(D goodAllocSize(b.length)
	== goodAllocSize(s)).
	*/
	bool reallocate(ref void[] b, size_t s)
	{
	if (!b.ptr)
	{
	b = allocate(s);
	return b.length == s;
	}
	if (s >= b.length && expand(b, s - b.length)) return true;
	immutable toAllocate = goodAllocSize(s),
	allocated = goodAllocSize(b.length);
	// Are the lengths within the same quantum?
	if (allocated == toAllocate)
	{
	// Reallocation (whether up or down) will be done in place
	b = b.ptr[0 .. s];
	return true;
	}
	// Defer to parent (or global) with quantized size
	auto original = b.ptr[0 .. allocated];
	if (!parent.reallocate(original, toAllocate)) return false;
	b = original.ptr[0 .. s];
	return true;
	}

	/**
	Defined only if `ParentAllocator.alignedAllocate` exists. Expansion
	occurs in place under the conditions required by `expand`. Shrinking
	occurs in place if $(D goodAllocSize(b.length) == goodAllocSize(s)).
	*/
	static if (hasMember!(ParentAllocator, "alignedAllocate"))
	bool alignedReallocate(ref void[] b, size_t s, uint a)
	{
	if (!b.ptr)
	{
	b = alignedAllocate(s, a);
	return b.length == s;
	}
	if (s >= b.length && b.ptr.alignedAt(a) && expand(b, s - b.length)) return true;
	immutable toAllocate = goodAllocSize(s),
	allocated = goodAllocSize(b.length);
	// Are the lengths within the same quantum?
	if (allocated == toAllocate && b.ptr.alignedAt(a))
	{
	assert(b.ptr); // code above must have caught this
	// Reallocation (whether up or down) will be done in place
	b = b.ptr[0 .. s];
	return true;
	}
	// Defer to parent (or global) with quantized size
	auto original = b.ptr[0 .. allocated];
	if (!parent.alignedReallocate(original, toAllocate, a)) return false;
	b = original.ptr[0 .. s];
	return true;
	}

	/**
	Defined if `ParentAllocator.deallocate` exists and forwards to
	$(D parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)])).
	*/
	static if (hasMember!(ParentAllocator, "deallocate"))
	bool deallocate(void[] b)
	{
	if (!b.ptr) return true;
	return parent.deallocate(b.ptr[0 .. goodAllocSize(b.length)]);
	}

	// Forwarding methods
	mixin(forwardToMember("parent",
	"allocateAll", "owns", "deallocateAll", "empty"));
	}

	///
	@system unittest
	{
	import std.experimental.allocator.building_blocks.free_tree : FreeTree;
	import std.experimental.allocator.gc_allocator : GCAllocator;

	size_t roundUpToMultipleOf(size_t s, uint base)
	{
	auto rem = s % base;
	return rem ? s + base - rem : s;
	}

	// Quantize small allocations to a multiple of cache line, large ones to a
	// multiple of page size
	alias MyAlloc = Quantizer!(
	FreeTree!GCAllocator,
	n => roundUpToMultipleOf(n, n <= 16_384 ? 64 : 4096));
	MyAlloc alloc;
	const buf = alloc.allocate(256);
	assert(buf.ptr);
	}

	version (StdUnittest)
	@system unittest
	{
	import std.experimental.allocator.gc_allocator : GCAllocator;
	alias MyAlloc = Quantizer!(GCAllocator,
	(size_t n) => n.roundUpToMultipleOf(64));
	testAllocator!(() => MyAlloc());

	assert((() pure nothrow @safe @nogc => MyAlloc().goodAllocSize(1))() == 64);

	auto a = MyAlloc();
	auto b = a.allocate(42);
	assert(b.length == 42);
	// Inplace expand, since goodAllocSize is 64
	assert((() @safe => a.expand(b, 22))());
	//assert((() nothrow @safe => a.expand(b, 22))());
	assert(b.length == 64);
	// Trigger parent.expand, which may or may not succed
	//() nothrow @safe { a.expand(b, 1); }();
	() @safe { a.expand(b, 1); }();
	assert(a.reallocate(b, 100));
	assert(b.length == 100);
	// Ensure deallocate inherits from parent
	() nothrow @nogc { a.deallocate(b); }();
	}

	@system unittest
	{
	import std.experimental.allocator.building_blocks.region : Region;
	import std.experimental.allocator.mallocator : Mallocator;
	import std.typecons : Ternary;

	alias Alloc = Quantizer!(Region!(Mallocator),
	(size_t n) => n.roundUpToMultipleOf(64));
	auto a = Alloc(Region!Mallocator(1024 * 64));
	const b = a.allocate(42);
	assert(b.length == 42);
	// Check that owns inherits from parent, i.e. Region
	assert((() pure nothrow @safe @nogc => a.owns(b))() == Ternary.yes);
	assert((() pure nothrow @safe @nogc => a.owns(null))() == Ternary.no);

	auto c = a.allocate(42);
	assert(c.length == 42);
	assert((() pure nothrow @safe @nogc => a.owns(c))() == Ternary.yes);
	// Inplace expand, since goodAllocSize is 64
	assert((() nothrow @safe => a.expand(c, 22))());
	assert(c.length == 64);
	// Trigger parent.expand
	assert((() nothrow @safe => a.expand(c, 1))());
	assert(c.length == 65);
	// Check that reallocate inherits from parent
	assert((() nothrow @nogc => a.reallocate(c, 100))());
	assert(c.length == 100);
	}

	version (StdUnittest)
	@system unittest
	{
	import std.experimental.allocator.building_blocks.region : Region;
	import std.experimental.allocator.mallocator : Mallocator;

	alias MyAlloc = Quantizer!(Region!(Mallocator),
	(size_t n) => n.roundUpToMultipleOf(64));
	testAllocator!(() => MyAlloc(Region!Mallocator(1024 * 64)));

	auto a = MyAlloc(Region!Mallocator(1024 * 64));
	void[] b;
	assert((() nothrow @nogc => a.alignedReallocate(b, 42, 16))());
	assert(b.length == 42);
	assert(alignedAt(&b[0], 16));
	}

	version (StdUnittest)
	@system unittest
	{
	import std.experimental.allocator.building_blocks.region : BorrowedRegion;
	import std.typecons : Ternary;

	alias MyAlloc = Quantizer!(BorrowedRegion!(),
	(size_t n) => n.roundUpToMultipleOf(64));
	testAllocator!(() => MyAlloc(BorrowedRegion!()(new ubyte[1024 * 64])));

	auto a = MyAlloc(BorrowedRegion!()(new ubyte[1024 * 64]));
	// Check that empty inherits from parent
	assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
	auto b = a.allocate(42);
	assert(b.length == 42);
	assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.no);
	// Check that deallocateAll inherits from parent
	assert((() nothrow @nogc => a.deallocateAll())());
	assert((() pure nothrow @safe @nogc => a.empty)() == Ternary.yes);
	}