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// Copyright 2019 The Marl Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#if !defined(_XOPEN_SOURCE)
// This must come before other #includes, otherwise we'll end up with ucontext_t
// definition mismatches, leading to memory corruption hilarity.
#define _XOPEN_SOURCE
#endif // !defined(_XOPEN_SOURCE)
#include "marl/debug.h"
#include <functional>
#include <memory>
#include <ucontext.h>
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
#endif // defined(__clang__)
namespace marl {
class OSFiber {
public:
// createFiberFromCurrentThread() returns a fiber created from the current
// thread.
static inline OSFiber* createFiberFromCurrentThread();
// createFiber() returns a new fiber with the given stack size that will
// call func when switched to. func() must end by switching back to another
// fiber, and must not return.
static inline OSFiber* createFiber(size_t stackSize,
const std::function<void()>& func);
// switchTo() immediately switches execution to the given fiber.
// switchTo() must be called on the currently executing fiber.
inline void switchTo(OSFiber*);
private:
std::unique_ptr<uint8_t[]> stack;
ucontext_t context;
std::function<void()> target;
};
OSFiber* OSFiber::createFiberFromCurrentThread() {
auto out = new OSFiber();
out->context = {};
getcontext(&out->context);
return out;
}
OSFiber* OSFiber::createFiber(size_t stackSize,
const std::function<void()>& func) {
union Args {
OSFiber* self;
struct {
int a;
int b;
};
};
struct Target {
static void Main(int a, int b) {
Args u;
u.a = a;
u.b = b;
std::function<void()> func;
std::swap(func, u.self->target);
func();
}
};
auto out = new OSFiber();
out->context = {};
out->stack = std::unique_ptr<uint8_t[]>(new uint8_t[stackSize]);
out->target = func;
auto alignmentOffset =
15 - (reinterpret_cast<uintptr_t>(out->stack.get() + 15) & 15);
auto res = getcontext(&out->context);
MARL_ASSERT(res == 0, "getcontext() returned %d", int(res));
out->context.uc_stack.ss_sp = out->stack.get() + alignmentOffset;
out->context.uc_stack.ss_size = stackSize - alignmentOffset;
out->context.uc_link = nullptr;
Args args;
args.self = out;
makecontext(&out->context, reinterpret_cast<void (*)()>(&Target::Main), 2,
args.a, args.b);
return out;
}
void OSFiber::switchTo(OSFiber* fiber) {
auto res = swapcontext(&context, &fiber->context);
MARL_ASSERT(res == 0, "swapcontext() returned %d", int(res));
}
} // namespace marl
#if defined(__clang__)
#pragma clang diagnostic pop
#endif // defined(__clang__)