/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.

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

    http://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.
==============================================================================*/

#define EIGEN_USE_THREADS

#include <deque>
#include <utility>

#include "third_party/eigen3/unsupported/Eigen/CXX11/Tensor"
#include "tensorflow/core/framework/resource_mgr.h"
#include "tensorflow/core/framework/variant.h"
#include "tensorflow/core/framework/variant_encode_decode.h"
#include "tensorflow/core/kernels/ops_util.h"
#include "tensorflow/core/lib/core/errors.h"
#include "tensorflow/core/lib/core/threadpool.h"
#include "tensorflow/core/platform/macros.h"
#include "tensorflow/core/platform/mutex.h"
#include "tensorflow/core/platform/types.h"

namespace tensorflow {

namespace {

class Mutex : public ResourceBase {
 public:
  explicit Mutex(OpKernelContext* c, const string& name)
      : locked_(false),
        thread_pool_(new thread::ThreadPool(
            c->env(), ThreadOptions(),
            strings::StrCat("mutex_lock_thread_", SanitizeThreadSuffix(name)),
            1 /* num_threads */, false /* low_latency_hint */)),
        name_(name) {
    VLOG(2) << "Creating mutex with name " << name << ": " << this;
  }

  string DebugString() override { return strings::StrCat("Mutex ", name_); }

  class LockReleaser {
   public:
    explicit LockReleaser(Mutex* mutex) : mutex_(mutex) {}

    LockReleaser(const LockReleaser&) = delete;
    LockReleaser& operator=(const LockReleaser&) = delete;

    virtual ~LockReleaser() {
      VLOG(3) << "Destroying LockReleaser " << this << " for mutex: " << mutex_;
      if (mutex_) {
        mutex_lock lock(mutex_->mu_);
        mutex_->locked_ = false;
        mutex_->cv_.notify_all();
        VLOG(3) << "Destroying LockReleaser " << this
                << ": sent notifications.";
      }
    }

   private:
    Mutex* mutex_;
  };

  struct SharedLockReleaser {
    std::shared_ptr<LockReleaser> shared_lock;

    explicit SharedLockReleaser(std::shared_ptr<LockReleaser>&& lock)
        : shared_lock(std::forward<decltype(lock)>(lock)) {
      VLOG(3) << "Creating shared_ptr of " << shared_lock.get()
              << " count is: " << shared_lock.use_count();
    }

    SharedLockReleaser(SharedLockReleaser&& rhs)
        : shared_lock(std::move(rhs.shared_lock)) {
      VLOG(3) << "Moving SharedLockReleaser of " << shared_lock.get()
              << " count is: " << shared_lock.use_count();
    }

    SharedLockReleaser(const SharedLockReleaser& rhs)
        : shared_lock(rhs.shared_lock) {
      VLOG(3) << "Copying SharedLockReleaser of " << shared_lock.get()
              << " count is: " << shared_lock.use_count();
    }

    ~SharedLockReleaser() {
      VLOG(3) << "Destroying SharedLockReleaser of " << shared_lock.get()
              << " count is: " << shared_lock.use_count();
    }

    void Encode(VariantTensorData*) const {
      // Not supported.
    }

    bool Decode(const VariantTensorData&) {
      return false;  // Not supported.
    }
  };

  void AcquireAsync(
      OpKernelContext* c,
      std::function<void(const Status& s, SharedLockReleaser lock)> fn) {
    CancellationManager* cm = c->cancellation_manager();
    CancellationToken token{};
    bool* cancelled = nullptr;
    if (cm) {
      cancelled = new bool(false);  // GUARDED_BY(mu_);
      token = cm->get_cancellation_token();
      const bool already_cancelled =
          !cm->RegisterCallback(token, [this, cancelled]() {
            mutex_lock lock(mu_);
            *cancelled = true;
            cv_.notify_all();
          });
      if (already_cancelled) {
        delete cancelled;
        fn(errors::Cancelled("Lock acquisition cancelled."),
           SharedLockReleaser{nullptr});
        return;
      }
    }
    thread_pool_->Schedule(std::bind(
        [this, cm, cancelled,
         token](std::function<void(const Status& s, SharedLockReleaser&& lock)>
                    fn_) {
          bool local_locked;
          {
            mutex_lock lock(mu_);
            while (locked_ && !(cancelled && *cancelled)) {
              cv_.wait(lock);
            }
            local_locked = locked_ = !(cancelled && *cancelled);
          }
          if (cm) {
            cm->DeregisterCallback(token);
            delete cancelled;
          }
          if (local_locked) {  // Not cancelled.
            fn_(Status::OK(),
                SharedLockReleaser{std::make_shared<LockReleaser>(this)});
          } else {
            fn_(errors::Cancelled("Lock acqusition cancelled."),
                SharedLockReleaser{nullptr});
          }
        },
        std::move(fn)));
  }

 private:
  mutex mu_;
  condition_variable cv_ GUARDED_BY(mu_);
  bool locked_ GUARDED_BY(mu_);
  std::unique_ptr<thread::ThreadPool> thread_pool_;
  string name_;
};

}  // namespace

class MutexLockOp : public AsyncOpKernel {
 public:
  explicit MutexLockOp(OpKernelConstruction* c) : AsyncOpKernel(c) {}

 public:
  void ComputeAsync(OpKernelContext* c, DoneCallback done) override {
    Mutex* mutex = nullptr;
    OP_REQUIRES_OK_ASYNC(
        c,
        LookupOrCreateResource<Mutex>(c, HandleFromInput(c, 0), &mutex,
                                      [c](Mutex** ptr) {
                                        *ptr = new Mutex(
                                            c, HandleFromInput(c, 0).name());
                                        return Status::OK();
                                      }),
        done);

    Tensor* variant;
    OP_REQUIRES_OK_ASYNC(c, c->allocate_output(0, TensorShape({}), &variant),
                         done);

    mutex->AcquireAsync(
        c, std::bind(
               [c, variant, mutex](DoneCallback done_,
                                   // End of bound arguments.
                                   const Status& s,
                                   Mutex::SharedLockReleaser&& lock) {
                 VLOG(2) << "Finished locking mutex " << mutex
                         << " with lock: " << lock.shared_lock.get()
                         << " status: " << s.ToString();
                 if (s.ok()) {
                   variant->scalar<Variant>()() = std::move(lock);
                 } else {
                   c->SetStatus(s);
                 }
                 mutex->Unref();
                 done_();
               },
               std::move(done), std::placeholders::_1, std::placeholders::_2));
  }
};

class ConsumeMutexLockOp : public OpKernel {
 public:
  explicit ConsumeMutexLockOp(OpKernelConstruction* context)
      : OpKernel(context) {}

  void Compute(OpKernelContext* c) override {
    VLOG(2) << "Executing ConsumeMutexLockOp";
    const Tensor& lock_t = c->input(0);
    OP_REQUIRES(
        c, lock_t.dims() == 0,
        errors::InvalidArgument("Expected input to be a scalar, saw shape: ",
                                lock_t.shape().DebugString()));
    OP_REQUIRES(
        c, lock_t.dtype() == DT_VARIANT,
        errors::InvalidArgument("Expected input to be a variant, saw type: ",
                                DataTypeString(lock_t.dtype())));
    const auto* lock =
        lock_t.scalar<Variant>()().get<Mutex::SharedLockReleaser>();
    OP_REQUIRES(c, lock,
                errors::InvalidArgument(
                    "Expected input to contain a SharedLockReleaser "
                    "object, but saw variant: '",
                    lock_t.scalar<Variant>()().DebugString(), "'"));
    const int use_count = lock->shared_lock.use_count();
    OP_REQUIRES(
        c, use_count == 1,
        errors::InvalidArgument("Expected use count of lock to be 1, but saw: ",
                                use_count));
  }

  bool IsExpensive() override { return false; }
};

REGISTER_KERNEL_BUILDER(Name("MutexLock").Device(DEVICE_CPU), MutexLockOp);

REGISTER_KERNEL_BUILDER(Name("MutexV2").Device(DEVICE_CPU),
                        ResourceHandleOp<Mutex>);

REGISTER_KERNEL_BUILDER(Name("ConsumeMutexLock").Device(DEVICE_CPU),
                        ConsumeMutexLockOp);

}  // namespace tensorflow