Method findOrCreate

bolt/common/caching/AsyncDataCache.cpp:168–236

}

CachePin CacheShard::findOrCreate(
    RawFileCacheKey key,
    uint64_t size,
    folly::SemiFuture<bool>* wait,
    bool cacheable) {
  AsyncDataCacheEntry* entryToInit = nullptr;
  {
    std::lock_guard<std::mutex> l(mutex_);
    ++eventCounter_;
    auto it = entryMap_.find(key);
    if (it != entryMap_.end()) {
      auto* found = it->second;
      if (found->isExclusive()) {
        ++numWaitExclusive_;
        if (wait == nullptr) {
          return CachePin();
        }
        *wait = found->getFuture();
        return CachePin();
      }
      if (found->size() >= size) {
        found->touch();
        // The entry is in a readable state. Add a pin.
        if (found->isPrefetch()) {
          found->isFirstUse_ = true;
          found->setPrefetch(false);
        } else {
          ++numHit_;
          hitBytes_ += found->size();
        }
        ++found->numPins_;
        CachePin pin;
        pin.setEntry(found);
        return pin;
      }

      // TODO: add stats to report or send alert in production.

      // This can happen if different load quanta apply to access via different
      // connectors. This is not an error but still worth logging.
      BOLT_CACHE_LOG_EVERY_MS(WARNING, 1'000)
          << "Requested larger entry. Found size " << found->size()
          << " requested size " << size;
      // The old entry is superseded. Possible readers of the old entry still
      // retain a valid read pin.
      found->key_.fileNum.clear();
    }

    auto newEntry = getFreeEntry();
    // Initialize the members that must be set inside 'mutex_'.
    newEntry->numPins_ = AsyncDataCacheEntry::kExclusive;
    newEntry->promise_ = nullptr;
    entryToInit = newEntry.get();
    entryMap_[key] = newEntry.get();
    if (emptySlots_.empty()) {
      entries_.push_back(std::move(newEntry));
    } else {
      const auto index = emptySlots_.back();