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Make SkFunction copyable so it can go in containers.

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This totally overhauls the implementation to use ordinary inheritance-based type erasure.  I give up for now getting my manual vtable shenanigans to work with MSVC.  Still those same "expected ; before ), also expected ) before ;" errors.

I added support for uninitialized SkFunctions and operator=(), because it was fairly straightforward with this implementation.

The main downside here is that I've removed the inline implementation.  All SkFunctions involve a heap allocation, even when just wrapping function pointers.

BUG=skia:

Review URL: https://codereview.chromium.org/1056673002
This commit is contained in:
mtklein 2015-05-06 07:40:25 -07:00 committed by Commit bot
parent 444987fea8
commit 0d992db1cf
2 changed files with 73 additions and 80 deletions
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104
src/core/SkFunction.h
View File

@ -8,94 +8,68 @@
#ifndef SkFunction_DEFINED
#define SkFunction_DEFINED
// TODO: document
// TODO: document, more pervasive move support in constructors, small-Fn optimization
#include "SkTemplates.h"
#include "SkTypes.h"
#include "SkTLogic.h"
template <typename> class SkFunction;
template <typename R, typename... Args>
class SkFunction<R(Args...)> : SkNoncopyable {
class SkFunction<R(Args...)> {
public:
SkFunction(R (*fn)(Args...)) : fVTable(GetFunctionPointerVTable()) {
// We've been passed a function pointer. We'll just store it.
fFunction = reinterpret_cast<void*>(fn);
}
SkFunction() {}
template <typename Fn>
SkFunction(Fn fn, SK_WHEN_C((sizeof(Fn) > sizeof(void*)), void*) = nullptr)
: fVTable(GetOutlineVTable<Fn>()) {
// We've got a functor larger than a pointer. We've go to copy it onto the heap.
fFunction = SkNEW_ARGS(Fn, (Forward(fn)));
SkFunction(const Fn& fn) : fFunction(SkNEW_ARGS(LambdaImpl<Fn>, (fn))) {}
SkFunction(R (*fn)(Args...)) : fFunction(SkNEW_ARGS(FnPtrImpl, (fn))) {}
SkFunction(const SkFunction& other) { *this = other; }
SkFunction& operator=(const SkFunction& other) {
if (this != &other) {
fFunction.reset(other.fFunction ? other.fFunction->clone() : nullptr);
}
return *this;
}
template <typename Fn>
SkFunction(Fn fn, SK_WHEN_C((sizeof(Fn) <= sizeof(void*)), void*) = nullptr)
: fVTable(GetInlineVTable<Fn>()) {
// We've got a functor that fits in a pointer. We copy it right inline.
fFunction = NULL; // Quiets a (spurious) warning that fFunction might be uninitialized.
SkNEW_PLACEMENT_ARGS(&fFunction, Fn, (Forward(fn)));
R operator()(Args... args) const {
SkASSERT(fFunction.get());
return fFunction->call(Forward(args)...);
}
~SkFunction() { fVTable.fCleanUp(fFunction); }
R operator()(Args... args) { return fVTable.fCall(fFunction, Forward(args)...); }
private:
// ~= std::forward. This moves its argument if possible, falling back to a copy if not.
template <typename T> static T&& Forward(T& v) { return (T&&)v; }
struct VTable {
R (*fCall)(void*, Args...);
void (*fCleanUp)(void*);
struct Interface {
virtual ~Interface() {}
virtual R call(Args...) const = 0;
virtual Interface* clone() const = 0;
};
// Used when fFunction is a function pointer of type R(*)(Args...).
static const VTable& GetFunctionPointerVTable() {
static const VTable vtable = {
[](void* fn, Args... args) {
return reinterpret_cast<R(*)(Args...)>(fn)(Forward(args)...);
},
[](void*) { /* Nothing to clean up for function pointers. */ }
};
return vtable;
}
// Used when fFunction is a pointer to a functor of type Fn on the heap (we own it).
template <typename Fn>
static const VTable& GetOutlineVTable() {
static const VTable vtable = {
[](void* fn, Args... args) { return (*static_cast<Fn*>(fn))(Forward(args)...); },
[](void* fn) { SkDELETE(static_cast<Fn*>(fn)); },
};
return vtable;
}
class LambdaImpl final : public Interface {
public:
LambdaImpl(const Fn& fn) : fFn(fn) {}
// Used when fFunction _is_ a functor of type Fn, not a pointer to the functor.
template <typename Fn>
static const VTable& GetInlineVTable() {
static const VTable vtable = {
[](void* fn, Args... args) {
union { void** p; Fn* f; } pun = { &fn };
return (*pun.f)(Forward(args)...);
},
[](void* fn) {
union { void** p; Fn* f; } pun = { &fn };
(*pun.f).~Fn();
(void)(pun.f); // Otherwise, when ~Fn() is trivial, MSVC complains pun is unused.
}
};
return vtable;
}
R call(Args... args) const override { return fFn(Forward(args)...); }
Interface* clone() const { return SkNEW_ARGS(LambdaImpl<Fn>, (fFn)); }
private:
Fn fFn;
};
class FnPtrImpl final : public Interface {
public:
FnPtrImpl(R (*fn)(Args...)) : fFn(fn) {}
void* fFunction; // A function pointer, a pointer to a functor, or an inlined functor.
const VTable& fVTable; // How to call, delete (and one day copy, move) fFunction.
R call(Args... args) const override { return fFn(Forward(args)...); }
Interface* clone() const { return SkNEW_ARGS(FnPtrImpl, (fFn)); }
private:
R (*fFn)(Args...);
};
SkAutoTDelete<Interface> fFunction;
};
// TODO:
// - is it worth moving fCall out of the VTable into SkFunction itself to avoid the indirection?
// - make SkFunction copyable
#endif//SkFunction_DEFINED

49
tests/FunctionTest.cpp
View File

@ -8,29 +8,31 @@
#include "SkFunction.h"
#include "Test.h"
static void test_add_five(skiatest::Reporter* r, SkFunction<int(int)>&& f) {
static void test_add_five(skiatest::Reporter* r, SkFunction<int(int)>& f) {
REPORTER_ASSERT(r, f(3) == 8);
REPORTER_ASSERT(r, f(4) == 9);
}
static void test_add_five(skiatest::Reporter* r, SkFunction<int(int)>&& f) { test_add_five(r, f); }
static int add_five(int x) { return x + 5; }
struct AddFive {
int operator()(int x) { return x + 5; };
int operator()(int x) const { return x + 5; };
};
class MoveOnlyAdd5 : SkNoncopyable {
class MoveOnlyThree : SkNoncopyable {
public:
MoveOnlyAdd5() {}
MoveOnlyAdd5(MoveOnlyAdd5&&) {}
MoveOnlyAdd5& operator=(MoveOnlyAdd5&&) { return *this; }
MoveOnlyThree() {}
MoveOnlyThree(MoveOnlyThree&&) {}
MoveOnlyThree& operator=(MoveOnlyThree&&) { return *this; }
int operator()(int x) { return x + 5; }
int val() { return 3; }
};
DEF_TEST(Function, r) {
// We should be able to turn a static function, an explicit functor, or a lambda
// all into an SkFunction equally well.
// We should be able to turn a function pointer, an explicit functor, or a
// lambda into an SkFunction all equally well.
test_add_five(r, &add_five);
test_add_five(r, AddFive());
test_add_five(r, [](int x) { return x + 5; });
@ -40,12 +42,29 @@ DEF_TEST(Function, r) {
int a = 1, b = 1, c = 1, d = 1, e = 1;
test_add_five(r, [&](int x) { return x + a + b + c + d + e; });
// Makes sure we forward the functor when constructing SkFunction.
test_add_five(r, MoveOnlyAdd5());
// Makes sure we forward arguments when calling SkFunction.
SkFunction<int(int, MoveOnlyAdd5&&, int)> f([](int x, MoveOnlyAdd5&& addFive, int y) {
return x * addFive(y);
SkFunction<int(int, MoveOnlyThree&&, int)> f([](int x, MoveOnlyThree&& three, int y) {
return x * three.val() + y;
});
REPORTER_ASSERT(r, f(2, MoveOnlyAdd5(), 4) == 18);
REPORTER_ASSERT(r, f(2, MoveOnlyThree(), 4) == 10);
// SkFunctions can go in containers.
SkTArray<SkFunction<int(int)>> add_fivers;
add_fivers.push_back(&add_five);
add_fivers.push_back(AddFive());
add_fivers.push_back([](int x) { return x + 5; });
add_fivers.push_back([&](int x) { return x + a + b + c + d + e; });
for (auto& f : add_fivers) {
test_add_five(r, f);
}
// SkFunctions are assignable.
SkFunction<int(int)> empty;
empty = [](int x) { return x + 5; };
test_add_five(r, empty);
// This all is silly acrobatics, but it should at least work correctly.
SkFunction<int(int)> emptyA, emptyB(emptyA);
emptyA = emptyB;
emptyA = emptyA;
}