/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef builtin_AtomicsObject_h
#define builtin_AtomicsObject_h

#include "mozilla/Maybe.h"
#include "mozilla/TimeStamp.h"

#include "threading/ConditionVariable.h"
#include "threading/ProtectedData.h"  // js::ThreadData
#include "vm/NativeObject.h"
#include "vm/PlainObject.h"

namespace js {

class SharedArrayRawBuffer;

class AtomicsObject : public NativeObject {
 public:
  static const JSClass class_;
};

enum class FutexWaiterKind { Sync, Async, ListHead };

class FutexWaiter;
class SyncFutexWaiter;
class AsyncFutexWaiter;

class FutexWaiterListNode {
 private:
  FutexWaiterListNode* next_ = nullptr;  // Lower priority node in waiter list
  FutexWaiterListNode* prev_ = nullptr;  // Higher priority node in waiter list

 protected:
  explicit FutexWaiterListNode(FutexWaiterKind kind) : kind_(kind) {}
  FutexWaiterKind kind_;

 public:
  FutexWaiter* toWaiter() {
    MOZ_ASSERT(kind_ != FutexWaiterKind::ListHead);
    return reinterpret_cast<FutexWaiter*>(this);
  }

  FutexWaiterKind kind() const { return kind_; }

  FutexWaiterListNode* next() { return next_; }
  void setNext(FutexWaiterListNode* next) { next_ = next; }
  FutexWaiterListNode* prev() { return prev_; }
  void setPrev(FutexWaiterListNode* prev) { prev_ = prev; }
};

class FutexWaiterListHead : public FutexWaiterListNode {
 public:
  FutexWaiterListHead() : FutexWaiterListNode(FutexWaiterKind::ListHead) {
    setNext(this);
    setPrev(this);
  }
  ~FutexWaiterListHead();
};

class FutexThread {
  friend class AutoLockFutexAPI;

 public:
  [[nodiscard]] static bool initialize();
  static void destroy();

  static void lock();
  static void unlock();

  FutexThread();
  [[nodiscard]] bool initInstance();
  void destroyInstance();

  // Parameters to notify().
  enum NotifyReason {
    NotifyExplicit,       // Being asked to wake up by another thread
    NotifyForJSInterrupt  // Interrupt requested
  };

  // Result codes from wait() and atomics_wait_impl().
  enum class WaitResult {
    Error,     // Error has been reported, just propagate error signal
    NotEqual,  // Did not wait because the values differed
    OK,        // Waited and was woken
    TimedOut   // Waited and timed out
  };

  // Block the calling thread and wait.
  //
  // The futex lock must be held around this call.
  //
  // The timeout is the number of milliseconds, with fractional
  // times allowed; specify mozilla::Nothing() for an indefinite
  // wait.
  //
  // wait() will not wake up spuriously.
  [[nodiscard]] WaitResult wait(
      JSContext* cx, js::UniqueLock<js::Mutex>& locked,
      const mozilla::Maybe<mozilla::TimeDuration>& timeout);

  // Notify the thread this is associated with.
  //
  // The futex lock must be held around this call.  (The sleeping
  // thread will not wake up until the caller of Atomics.notify()
  // releases the lock.)
  //
  // If the thread is not waiting then this method does nothing.
  //
  // If the thread is waiting in a call to wait() and the
  // reason is NotifyExplicit then the wait() call will return
  // with Woken.
  //
  // If the thread is waiting in a call to wait() and the
  // reason is NotifyForJSInterrupt then the wait() will return
  // with WaitingNotifiedForInterrupt; in the latter case the caller
  // of wait() must handle the interrupt.
  void notify(NotifyReason reason);

  bool isWaiting();

  // If canWait() returns false (the default) then wait() is disabled
  // on the thread to which the FutexThread belongs.
  bool canWait() { return canWait_; }

  void setCanWait(bool flag) { canWait_ = flag; }

 private:
  enum FutexState {
    Idle,                         // We are not waiting or woken
    Waiting,                      // We are waiting, nothing has happened yet
    WaitingNotifiedForInterrupt,  // We are waiting, but have been interrupted,
                                  //   and have not yet started running the
                                  //   interrupt handler
    WaitingInterrupted,           // We are waiting, but have been interrupted
                                  //   and are running the interrupt handler
    Woken                         // Woken by a script call to Atomics.notify
  };

  // Condition variable that this runtime will wait on.
  js::ConditionVariable* cond_;

  // Current futex state for this runtime.  When not in a wait this
  // is Idle; when in a wait it is Waiting or the reason the futex
  // is about to wake up.
  FutexState state_;

  // Shared futex lock for all runtimes.  We can perhaps do better,
  // but any lock will need to be per-domain (consider SharedWorker)
  // or coarser.
  static mozilla::Atomic<js::Mutex*, mozilla::SequentiallyConsistent> lock_;

  // A flag that controls whether waiting is allowed.
  ThreadData<bool> canWait_;
};

// Go to sleep if the int32_t value at the given address equals `value`.
[[nodiscard]] FutexThread::WaitResult atomics_wait_impl(
    JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int32_t value,
    const mozilla::Maybe<mozilla::TimeDuration>& timeout);

// Go to sleep if the int64_t value at the given address equals `value`.
[[nodiscard]] FutexThread::WaitResult atomics_wait_impl(
    JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int64_t value,
    const mozilla::Maybe<mozilla::TimeDuration>& timeout);

// If the int32_t value at the given address equals `value`, return a result
// object containing a promise that will be resolved when that address is
// notified.
[[nodiscard]] PlainObject* atomics_wait_async_impl(
    JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int32_t value,
    const mozilla::Maybe<mozilla::TimeDuration>& timeout);

// If the int64_t value at the given address equals `value`, return a result
// object containing a promise that will be resolved when that address is
// notified.
[[nodiscard]] PlainObject* atomics_wait_async_impl(
    JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int64_t value,
    const mozilla::Maybe<mozilla::TimeDuration>& timeout);

// Notify some waiters on the given address.  If `count` is negative then notify
// all.  The return value is nonnegative and is the number of waiters woken.  If
// the number of waiters woken exceeds INT64_MAX then this never returns.  If
// `count` is nonnegative then the woken out parameter is never greater than
// `count`.
[[nodiscard]] bool atomics_notify_impl(JSContext* cx,
                                       SharedArrayRawBuffer* sarb,
                                       size_t byteOffset, int64_t count,
                                       int64_t* woken);

} /* namespace js */

#endif /* builtin_AtomicsObject_h */