Bug 1868456: Improve ManagedPostRefreshObserver invariants. a=dmeehan

#include "nsRefreshObservers.h"

#include "nsPresContext.h"

#include "mozilla/Likely.h"

namespace mozilla {

    : mPresContext(aPc), mAction(std::move(aAction)) {}

ManagedPostRefreshObserver::ManagedPostRefreshObserver(nsPresContext* aPc)

    : mPresContext(aPc) {}

    : mPresContext(aPc) {

  MOZ_ASSERT(mPresContext, "Can't observe without a nsPresContext");

}

ManagedPostRefreshObserver::~ManagedPostRefreshObserver() = default;

void ManagedPostRefreshObserver::Cancel() {

  // Caller holds a strong reference, so no need to reference stuff from here.

  if (mAction) {

    mAction(true);

  }

  mAction = nullptr;

  mPresContext = nullptr;

}

void ManagedPostRefreshObserver::DidRefresh() {

  if (MOZ_UNLIKELY(!mAction)) {

    return;

  }

  RefPtr<ManagedPostRefreshObserver> thisObject = this;

  auto action = std::move(mAction);

  Unregister unregister = action(false);

  Unregister unregister = mAction(false);

  if (unregister == Unregister::Yes) {

    if (RefPtr<nsPresContext> pc = std::move(mPresContext)) {

      // In theory mAction could've ended up in `Cancel` being called. In which

      // case we're already unregistered so no need to do anything.

      mAction = nullptr;

      // We have to null-check mPresContext here because in theory, mAction

      // could've ended up in `Cancel` being called, which would clear

      // mPresContext. In that case, we're already unregistered so no need to

      // do anything.

      pc->UnregisterManagedPostRefreshObserver(this);

    } else {

      MOZ_DIAGNOSTIC_ASSERT(!mAction);

    }

  } else {

    mAction = std::move(action);

  }

}