// 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.

// Minimal assembly implementations of fiber context switching for Unix-based
// platforms.
//
// Note: Unlike makecontext, swapcontext or the Windows fiber APIs, these
// assembly implementations *do not* save or restore signal masks,
// floating-point control or status registers, FS and GS segment registers,
// thread-local storage state nor any SIMD registers. This should not be a
// problem as the marl scheduler requires fibers to be executed on a single
// thread.

#if defined(__x86_64__)
#include "osfiber_asm_x64.h"
#elif defined(__i386__)
#include "osfiber_asm_x86.h"
#elif defined(__aarch64__)
#include "osfiber_asm_aarch64.h"
#elif defined(__arm__)
#include "osfiber_asm_arm.h"
#elif defined(__powerpc64__)
#include "osfiber_asm_ppc64.h"
#else
#error "Unsupported target"
#endif

#include <functional>
#include <memory>

extern "C" {

extern void marl_fiber_set_target(marl_fiber_context*,
                                  void* stack,
                                  uint32_t stack_size,
                                  void (*target)(void*),
                                  void* arg);
extern void marl_fiber_swap(marl_fiber_context* from,
                            const marl_fiber_context* to);

}  // extern "C"

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:
  static inline void run(OSFiber* self);

  marl_fiber_context context;
  std::function<void()> target;
  std::unique_ptr<uint8_t[]> stack;
};

OSFiber* OSFiber::createFiberFromCurrentThread() {
  auto out = new OSFiber();
  out->context = {};
  return out;
}

OSFiber* OSFiber::createFiber(size_t stackSize,
                              const std::function<void()>& func) {
  auto out = new OSFiber();
  out->context = {};
  out->target = func;
  out->stack = std::unique_ptr<uint8_t[]>(new uint8_t[stackSize]);
  marl_fiber_set_target(&out->context, out->stack.get(), stackSize,
                        reinterpret_cast<void (*)(void*)>(&OSFiber::run), out);
  return out;
}

void OSFiber::run(OSFiber* self) {
  self->target();
}

void OSFiber::switchTo(OSFiber* fiber) {
  marl_fiber_swap(&context, &fiber->context);
}

}  // namespace marl