C++ Lazy::get方法代码示例

const Metadata *
swift::_searchConformancesByMangledTypeName(const llvm::StringRef typeName) {
  auto &C = Conformances.get();
  const Metadata *foundMetadata = nullptr;

  pthread_mutex_lock(&C.SectionsToScanLock);

  unsigned sectionIdx = 0;
  unsigned endSectionIdx = C.SectionsToScan.size();

  for (; sectionIdx < endSectionIdx; ++sectionIdx) {
    auto &section = C.SectionsToScan[sectionIdx];
    for (const auto &record : section) {
      if (auto metadata = record.getCanonicalTypeMetadata())
        foundMetadata = _matchMetadataByMangledTypeName(typeName, metadata, nullptr);
      else if (auto pattern = record.getGenericPattern())
        foundMetadata = _matchMetadataByMangledTypeName(typeName, nullptr, pattern);

      if (foundMetadata != nullptr)
        break;
    }
    if (foundMetadata != nullptr)
      break;
  }

  pthread_mutex_unlock(&C.SectionsToScanLock);

  return foundMetadata;
}

const Metadata *
swift::_searchConformancesByMangledTypeName(const llvm::StringRef typeName) {
  auto &C = Conformances.get();
  const Metadata *foundMetadata = nullptr;

  ScopedLock guard(C.SectionsToScanLock);

  unsigned sectionIdx = 0;
  unsigned endSectionIdx = C.SectionsToScan.size();

  for (; sectionIdx < endSectionIdx; ++sectionIdx) {
    auto &section = C.SectionsToScan[sectionIdx];
    for (const auto &record : section) {
      if (auto metadata = record.getCanonicalTypeMetadata())
        foundMetadata = _matchMetadataByMangledTypeName(typeName, metadata, nullptr);
      else if (auto ntd = record.getNominalTypeDescriptor())
        foundMetadata = _matchMetadataByMangledTypeName(typeName, nullptr, ntd);

      if (foundMetadata != nullptr)
        break;
    }
    if (foundMetadata != nullptr)
      break;
  }

  return foundMetadata;
}

/// Search the witness table in the ConformanceCache. \returns a pair of the
/// WitnessTable pointer and a boolean value True if a definitive value is
/// found. \returns false if the type or its superclasses were not found in
/// the cache.
static
std::pair<const WitnessTable *, bool>
searchInConformanceCache(const Metadata *type,
                         const ProtocolDescriptor *protocol,
                         ConformanceCacheEntry *&foundEntry) {
  auto &C = Conformances.get();
  auto origType = type;

  foundEntry = nullptr;

recur_inside_cache_lock:

  // See if we have a cached conformance. Try the specific type first.

  {
    // Check if the type-protocol entry exists in the cache entry that we found.
    if (auto *Value = C.findCached(type, protocol)) {
      if (Value->isSuccessful())
        return std::make_pair(Value->getWitnessTable(), true);

      // If we're still looking up for the original type, remember that
      // we found an exact match.
      if (type == origType)
        foundEntry = Value;

      // If we got a cached negative response, check the generation number.
      if (Value->getFailureGeneration() == C.SectionsToScan.size()) {
        // We found an entry with a negative value.
        return std::make_pair(nullptr, true);
      }
    }
  }

  {
    // For generic and resilient types, nondependent conformances
    // are keyed by the nominal type descriptor rather than the
    // metadata, so try that.
    auto *description = type->getNominalTypeDescriptor().get();

    // Hash and lookup the type-protocol pair in the cache.
    if (auto *Value = C.findCached(description, protocol)) {
      if (Value->isSuccessful())
        return std::make_pair(Value->getWitnessTable(), true);

      // We don't try to cache negative responses for generic
      // patterns.
    }
  }

  // If the type is a class, try its superclass.
  if (const ClassMetadata *classType = type->getClassObject()) {
    if (classHasSuperclass(classType)) {
      type = swift_getObjCClassMetadata(classType->SuperClass);
      goto recur_inside_cache_lock;
    }
  }

  // We did not find an entry.
  return std::make_pair(nullptr, false);
}

static const TypeContextDescriptor *
_findNominalTypeDescriptor(Demangle::NodePointer node) {
  const TypeContextDescriptor *foundNominal = nullptr;
  auto &T = TypeMetadataRecords.get();

  auto mangledName = Demangle::mangleNode(node);

  // Look for an existing entry.
  // Find the bucket for the metadata entry.
  if (auto Value = T.NominalCache.find(mangledName))
    return Value->getDescription();

  // Check type metadata records
  T.SectionsToScanLock.withLock([&] {
    foundNominal = _searchTypeMetadataRecords(T, node);
  });

  // Check protocol conformances table. Note that this has no support for
  // resolving generic types yet.
  if (!foundNominal)
    foundNominal = _searchConformancesByMangledTypeName(node);

  if (foundNominal) {
    T.NominalCache.getOrInsert(mangledName, foundNominal);
  }

  return foundNominal;
}

static const TypeContextDescriptor *
_findNominalTypeDescriptor(Demangle::NodePointer node,
                           Demangle::Demangler &Dem) {
  const TypeContextDescriptor *foundNominal = nullptr;
  auto &T = TypeMetadataRecords.get();

  // If we have a symbolic reference to a context, resolve it immediately.
  NodePointer symbolicNode = node;
  if (symbolicNode->getKind() == Node::Kind::Type)
    symbolicNode = symbolicNode->getChild(0);
  if (symbolicNode->getKind() == Node::Kind::SymbolicReference)
    return cast<TypeContextDescriptor>(
      (const ContextDescriptor *)symbolicNode->getIndex());

  auto mangledName =
    Demangle::mangleNode(node,
                         [&](const void *context) -> NodePointer {
                           return _buildDemanglingForContext(
                               (const ContextDescriptor *) context,
                               {}, false, Dem);
                         });

  // Look for an existing entry.
  // Find the bucket for the metadata entry.
  if (auto Value = T.NominalCache.find(mangledName))
    return Value->getDescription();

  // Check type metadata records
  foundNominal = _searchTypeMetadataRecords(T, node);

  // Check protocol conformances table. Note that this has no support for
  // resolving generic types yet.
  if (!foundNominal)
    foundNominal = _searchConformancesByMangledTypeName(node);

  if (foundNominal) {
    T.NominalCache.getOrInsert(mangledName, foundNominal);
  }

  return foundNominal;
}

static const Metadata *
_typeByMangledName(const llvm::StringRef typeName) {
  const Metadata *foundMetadata = nullptr;
  auto &T = TypeMetadataRecords.get();

  // Look for an existing entry.
  // Find the bucket for the metadata entry.
  if (auto Value = T.Cache.find(typeName))
    return Value->getMetadata();

  // Check type metadata records
  pthread_mutex_lock(&T.SectionsToScanLock);
  foundMetadata = _searchTypeMetadataRecords(T, typeName);
  pthread_mutex_unlock(&T.SectionsToScanLock);

  // Check protocol conformances table. Note that this has no support for
  // resolving generic types yet.
  if (!foundMetadata)
    foundMetadata = _searchConformancesByMangledTypeName(typeName);

  if (foundMetadata) {
    T.Cache.getOrInsert(typeName, foundMetadata);
  }

#if SWIFT_OBJC_INTEROP
  // Check for ObjC class
  // FIXME does this have any value? any ObjC class with a Swift name
  // should already be registered as a Swift type.
  if (foundMetadata == nullptr) {
    std::string prefixedName("_Tt" + typeName.str());
    foundMetadata = reinterpret_cast<ClassMetadata *>
      (objc_lookUpClass(prefixedName.c_str()));
  }
#endif

  return foundMetadata;
}

static BoxPair::Return _swift_allocBox_(const Metadata *type) {
  // Get the heap metadata for the box.
  auto &B = Boxes.get();
  const void *typeArg = type;
  auto entry = B.findOrAdd(&typeArg, 1, [&]() -> BoxCacheEntry* {
    // Create a new entry for the box.
    auto entry = BoxCacheEntry::allocate(B.getAllocator(), &typeArg, 1, 0);

    auto metadata = entry->getData();
    metadata->Offset = GenericBoxHeapMetadata::getHeaderOffset(type);
    metadata->BoxedType = type;

    return entry;
  });

  auto metadata = entry->getData();

  // Allocate and project the box.
  auto allocation = swift_allocObject(metadata, metadata->getAllocSize(),
                                      metadata->getAllocAlignMask());
  auto projection = metadata->project(allocation);

  return BoxPair{allocation, projection};
}

void
swift::swift_registerTypeMetadataRecords(const TypeMetadataRecord *begin,
                                         const TypeMetadataRecord *end) {
  auto &T = TypeMetadataRecords.get();
  _registerTypeMetadataRecords(T, begin, end);
}

const WitnessTable *
swift::swift_conformsToProtocol(const Metadata *type,
                                const ProtocolDescriptor *protocol) {
  auto &C = Conformances.get();
  auto origType = type;
  unsigned numSections = 0;
  ConformanceCacheEntry *foundEntry;

recur:
  // See if we have a cached conformance. The ConcurrentMap data structure
  // allows us to insert and search the map concurrently without locking.
  // We do lock the slow path because the SectionsToScan data structure is not
  // concurrent.
  auto FoundConformance = searchInConformanceCache(type, protocol, foundEntry);
  // The negative answer does not always mean that there is no conformance,
  // unless it is an exact match on the type. If it is not an exact match,
  // it may mean that all of the superclasses do not have this conformance,
  // but the actual type may still have this conformance.
  if (FoundConformance.second) {
    if (FoundConformance.first || foundEntry)
      return FoundConformance.first;
  }

  // If we didn't have an up-to-date cache entry, scan the conformance records.
  C.SectionsToScanLock.lock();
  unsigned failedGeneration = ConformanceCacheGeneration;

  // If we have no new information to pull in (and nobody else pulled in
  // new information while we waited on the lock), we're done.
  if (C.SectionsToScan.size() == numSections) {
    if (failedGeneration != ConformanceCacheGeneration) {
      // Someone else pulled in new conformances while we were waiting.
      // Start over with our newly-populated cache.
      C.SectionsToScanLock.unlock();
      type = origType;
      goto recur;
    }


    // Save the failure for this type-protocol pair in the cache.
    C.cacheFailure(type, protocol);

    C.SectionsToScanLock.unlock();
    return nullptr;
  }

  // Update the last known number of sections to scan.
  numSections = C.SectionsToScan.size();

  // Scan only sections that were not scanned yet.
  unsigned sectionIdx = foundEntry ? foundEntry->getFailureGeneration() : 0;
  unsigned endSectionIdx = C.SectionsToScan.size();

  for (; sectionIdx < endSectionIdx; ++sectionIdx) {
    auto &section = C.SectionsToScan[sectionIdx];
    // Eagerly pull records for nondependent witnesses into our cache.
    for (const auto &record : section) {
      // If the record applies to a specific type, cache it.
      if (auto metadata = record.getCanonicalTypeMetadata()) {
        auto P = record.getProtocol();

        // Look for an exact match.
        if (protocol != P)
          continue;

        if (!isRelatedType(type, metadata, /*isMetadata=*/true))
          continue;

        // Store the type-protocol pair in the cache.
        auto witness = record.getWitnessTable(metadata);
        if (witness) {
          C.cacheSuccess(metadata, P, witness);
        } else {
          C.cacheFailure(metadata, P);
        }

      // If the record provides a nondependent witness table for all instances
      // of a generic type, cache it for the generic pattern.
      // TODO: "Nondependent witness table" probably deserves its own flag.
      // An accessor function might still be necessary even if the witness table
      // can be shared.
      } else if (record.getTypeKind()
                   == TypeMetadataRecordKind::UniqueNominalTypeDescriptor
                 && record.getConformanceKind()
                   == ProtocolConformanceReferenceKind::WitnessTable) {

        auto R = record.getNominalTypeDescriptor();
        auto P = record.getProtocol();

        // Look for an exact match.
        if (protocol != P)
          continue;

        if (!isRelatedType(type, R, /*isMetadata=*/false))
          continue;

        // Store the type-protocol pair in the cache.
        C.cacheSuccess(R, P, record.getStaticWitnessTable());
      }
    }
//.........这里部分代码省略.........

void
swift::swift_registerProtocolConformances(const ProtocolConformanceRecord *begin,
                                          const ProtocolConformanceRecord *end){
  auto &C = Conformances.get();
  _registerProtocolConformances(C, begin, end);
}

 Laziness()
 : total([&]{ return first.get()+ second.get(); }, total.depends(first).depends(second))
 {}

/// Search the witness table in the ConformanceCache. \returns a pair of the
/// WitnessTable pointer and a boolean value True if a definitive value is
/// found. \returns false if the type or its superclasses were not found in
/// the cache.
static
std::pair<const WitnessTable *, bool>
searchInConformanceCache(const Metadata *type,
                         const ProtocolDescriptor *protocol,
                         ConformanceCacheEntry *&foundEntry) {
  auto &C = Conformances.get();
  auto origType = type;

  foundEntry = nullptr;

recur_inside_cache_lock:

  // See if we have a cached conformance. Try the specific type first.

  // Hash and lookup the type-protocol pair in the cache.
  size_t hash = hashTypeProtocolPair(type, protocol);
  ConcurrentList<ConformanceCacheEntry> &Bucket =
    C.Cache.findOrAllocateNode(hash);

  // Check if the type-protocol entry exists in the cache entry that we found.
  for (auto &Entry : Bucket) {
    if (!Entry.matches(type, protocol)) continue;

    if (Entry.isSuccessful()) {
      return std::make_pair(Entry.getWitnessTable(), true);
    }

    if (type == origType)
      foundEntry = &Entry;

    // If we got a cached negative response, check the generation number.
    if (Entry.getFailureGeneration() == C.SectionsToScan.size()) {
      // We found an entry with a negative value.
      return std::make_pair(nullptr, true);
    }
  }

  // If the type is generic, see if there's a shared nondependent witness table
  // for its instances.
  if (auto generic = type->getGenericPattern()) {
    // Hash and lookup the type-protocol pair in the cache.
    size_t hash = hashTypeProtocolPair(generic, protocol);
    ConcurrentList<ConformanceCacheEntry> &Bucket =
      C.Cache.findOrAllocateNode(hash);

    for (auto &Entry : Bucket) {
      if (!Entry.matches(generic, protocol)) continue;
      if (Entry.isSuccessful()) {
        return std::make_pair(Entry.getWitnessTable(), true);
      }
      // We don't try to cache negative responses for generic
      // patterns.
    }
  }

  // If the type is a class, try its superclass.
  if (const ClassMetadata *classType = type->getClassObject()) {
    if (classHasSuperclass(classType)) {
      type = swift_getObjCClassMetadata(classType->SuperClass);
      goto recur_inside_cache_lock;
    }
  }

  // We did not find an entry.
  return std::make_pair(nullptr, false);
}

const WitnessTable *
swift::swift_conformsToProtocol(const Metadata * const type,
                                const ProtocolDescriptor *protocol) {
  auto &C = Conformances.get();

  // See if we have a cached conformance. The ConcurrentMap data structure
  // allows us to insert and search the map concurrently without locking.
  // We do lock the slow path because the SectionsToScan data structure is not
  // concurrent.
  auto FoundConformance = searchInConformanceCache(type, protocol);
  // If the result (positive or negative) is authoritative, return it.
  if (FoundConformance.isAuthoritative)
    return FoundConformance.witnessTable;

  auto failureEntry = FoundConformance.failureEntry;

  // No up-to-date cache entry found.
  // Acquire the lock so we can scan conformance records.
  ScopedLock guard(C.SectionsToScanLock);

  // The world may have changed while we waited for the lock.
  // If we found an out-of-date negative cache entry before
  // acquiring the lock, make sure the entry is still negative and out of date.
  // If we found no entry before acquiring the lock, search the cache again.
  if (failureEntry) {
    if (failureEntry->isSuccessful()) {
      // Somebody else found a conformance.
      return failureEntry->getWitnessTable();
    }
    if (failureEntry->getFailureGeneration() == C.SectionsToScan.size()) {
      // Somebody else brought the negative cache entry up to date.
      return nullptr;
    }
  }
  else {
    FoundConformance = searchInConformanceCache(type, protocol);
    if (FoundConformance.isAuthoritative) {
      // Somebody else found a conformance or cached an up-to-date failure.
      return FoundConformance.witnessTable;
    }
    failureEntry = FoundConformance.failureEntry;
  }

  // We are now caught up after acquiring the lock.
  // Prepare to scan conformance records.

  // Scan only sections that were not scanned yet.
  // If we found an out-of-date negative cache entry,
  // we need not to re-scan the sections that it covers.
  unsigned startSectionIdx =
    failureEntry ? failureEntry->getFailureGeneration() : 0;

  unsigned endSectionIdx = C.SectionsToScan.size();

  // If there are no unscanned sections outstanding
  // then we can cache failure and give up now.
  if (startSectionIdx == endSectionIdx) {
    C.cacheFailure(type, protocol);
    return nullptr;
  }

  // Really scan conformance records.

  for (unsigned sectionIdx = startSectionIdx;
       sectionIdx < endSectionIdx;
       ++sectionIdx) {
    auto &section = C.SectionsToScan[sectionIdx];
    // Eagerly pull records for nondependent witnesses into our cache.
    for (const auto &record : section) {
      // If the record applies to a specific type, cache it.
      if (auto metadata = record.getCanonicalTypeMetadata()) {
        auto P = record.getProtocol();

        // Look for an exact match.
        if (protocol != P)
          continue;

        if (!isRelatedType(type, metadata, /*candidateIsMetadata=*/true))
          continue;

        // Store the type-protocol pair in the cache.
        auto witness = record.getWitnessTable(metadata);
        if (witness) {
          C.cacheSuccess(metadata, P, witness);
        } else {
          C.cacheFailure(metadata, P);
        }

      // TODO: "Nondependent witness table" probably deserves its own flag.
      // An accessor function might still be necessary even if the witness table
      // can be shared.
      } else if (record.getTypeKind()
                   == TypeMetadataRecordKind::UniqueNominalTypeDescriptor) {

        auto R = record.getNominalTypeDescriptor();
        auto P = record.getProtocol();

        // Look for an exact match.
        if (protocol != P)
          continue;
//.........这里部分代码省略.........

/// Search for a witness table in the ConformanceCache.
static
ConformanceCacheResult
searchInConformanceCache(const Metadata *type,
                         const ProtocolDescriptor *protocol) {
  auto &C = Conformances.get();
  auto origType = type;
  ConformanceCacheEntry *failureEntry = nullptr;

recur:
  {
    // Try the specific type first.
    if (auto *Value = C.findCached(type, protocol)) {
      if (Value->isSuccessful()) {
        // Found a conformance on the type or some superclass. Return it.
        return ConformanceCacheResult::cachedSuccess(Value->getWitnessTable());
      }

      // Found a negative cache entry.

      bool isAuthoritative;
      if (type == origType) {
        // This negative cache entry is for the original query type.
        // Remember it so it can be returned later.
        failureEntry = Value;
        // An up-to-date entry for the original type is authoritative.
        isAuthoritative = true;
      } else {
        // An up-to-date cached failure for a superclass of the type is not
        // authoritative: there may be a still-undiscovered conformance
        // for the original query type.
        isAuthoritative = false;
      }

      // Check if the negative cache entry is up-to-date.
      // FIXME: Using SectionsToScan.size() outside SectionsToScanLock
      // is undefined.
      if (Value->getFailureGeneration() == C.SectionsToScan.size()) {
        // Negative cache entry is up-to-date. Return failure along with
        // the original query type's own cache entry, if we found one.
        // (That entry may be out of date but the caller still has use for it.)
        return ConformanceCacheResult::cachedFailure(failureEntry,
                                                     isAuthoritative);
      }

      // Negative cache entry is out-of-date.
      // Continue searching for a better result.
    }
  }

  {
    // For generic and resilient types, nondependent conformances
    // are keyed by the nominal type descriptor rather than the
    // metadata, so try that.
    const auto description = type->getNominalTypeDescriptor().get();

    // Hash and lookup the type-protocol pair in the cache.
    if (auto *Value = C.findCached(description, protocol)) {
      if (Value->isSuccessful())
        return ConformanceCacheResult::cachedSuccess(Value->getWitnessTable());

      // We don't try to cache negative responses for generic
      // patterns.
    }
  }

  // If the type is a class, try its superclass.
  if (const ClassMetadata *classType = type->getClassObject()) {
    if (classHasSuperclass(classType)) {
      type = swift_getObjCClassMetadata(classType->SuperClass);
      goto recur;
    }
  }

  // We did not find an up-to-date cache entry.
  // If we found an out-of-date entry for the original query type then
  // return it (non-authoritatively). Otherwise return a cache miss.
  if (failureEntry)
    return ConformanceCacheResult::cachedFailure(failureEntry, false);
  else
    return ConformanceCacheResult::cacheMiss();
}