llvm-project/clang-tools-extra/clangd/index/BackgroundIndexStorage.cpp

//== BackgroundIndexStorage.cpp - Provide caching support to BackgroundIndex ==/
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "Logger.h"
#include "index/Background.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/SHA1.h"

namespace clang {
namespace clangd {
namespace {

using FileDigest = decltype(llvm::SHA1::hash({}));

static FileDigest digest(StringRef Content) {
  return llvm::SHA1::hash({(const uint8_t *)Content.data(), Content.size()});
}

std::string getShardPathFromFilePath(llvm::StringRef ShardRoot,
                                     llvm::StringRef FilePath) {
  llvm::SmallString<128> ShardRootSS(ShardRoot);
  llvm::sys::path::append(ShardRootSS, llvm::sys::path::filename(FilePath) +
                                           "." + llvm::toHex(digest(FilePath)) +
                                           ".idx");
  return ShardRootSS.str();
}

llvm::Error
writeAtomically(llvm::StringRef OutPath,
                llvm::function_ref<void(llvm::raw_ostream &)> Writer) {
  // Write to a temporary file first.
  llvm::SmallString<128> TempPath;
  int FD;
  auto EC =
      llvm::sys::fs::createUniqueFile(OutPath + ".tmp.%%%%%%%%", FD, TempPath);
  if (EC)
    return llvm::errorCodeToError(EC);
  // Make sure temp file is destroyed on failure.
  auto RemoveOnFail =
      llvm::make_scope_exit([TempPath] { llvm::sys::fs::remove(TempPath); });
  llvm::raw_fd_ostream OS(FD, /*shouldClose=*/true);
  Writer(OS);
  OS.close();
  if (OS.has_error())
    return llvm::errorCodeToError(OS.error());
  // Then move to real location.
  EC = llvm::sys::fs::rename(TempPath, OutPath);
  if (EC)
    return llvm::errorCodeToError(EC);
  // If everything went well, we already moved the file to another name. So
  // don't delete the file, as the name might be taken by another file.
  RemoveOnFail.release();
  return llvm::ErrorSuccess();
}

// Uses disk as a storage for index shards. Creates a directory called
// ".clangd-index/" under the path provided during construction.
class DiskBackedIndexStorage : public BackgroundIndexStorage {
  std::string DiskShardRoot;

public:
  // Sets DiskShardRoot to (Directory + ".clangd-index/") which is the base
  // directory for all shard files.
  DiskBackedIndexStorage(llvm::StringRef Directory) {
    llvm::SmallString<128> CDBDirectory(Directory);
    llvm::sys::path::append(CDBDirectory, ".clangd-index/");
    DiskShardRoot = CDBDirectory.str();
    std::error_code OK;
    std::error_code EC = llvm::sys::fs::create_directory(DiskShardRoot);
    if (EC != OK) {
      elog("Failed to create directory {0} for index storage: {1}",
           DiskShardRoot, EC.message());
    }
  }

  std::unique_ptr<IndexFileIn>
  loadShard(llvm::StringRef ShardIdentifier) const override {
    const std::string ShardPath =
        getShardPathFromFilePath(DiskShardRoot, ShardIdentifier);
    auto Buffer = llvm::MemoryBuffer::getFile(ShardPath);
    if (!Buffer)
      return nullptr;
    if (auto I = readIndexFile(Buffer->get()->getBuffer()))
      return llvm::make_unique<IndexFileIn>(std::move(*I));
    else
      elog("Error while reading shard {0}: {1}", ShardIdentifier,
           I.takeError());
    return nullptr;
  }

  llvm::Error storeShard(llvm::StringRef ShardIdentifier,
                         IndexFileOut Shard) const override {
    return writeAtomically(
        getShardPathFromFilePath(DiskShardRoot, ShardIdentifier),
        [&Shard](llvm::raw_ostream &OS) { OS << Shard; });
  }
};

// Doesn't persist index shards anywhere (used when the CDB dir is unknown).
// We could consider indexing into ~/.clangd/ or so instead.
class NullStorage : public BackgroundIndexStorage {
public:
  std::unique_ptr<IndexFileIn>
  loadShard(llvm::StringRef ShardIdentifier) const override {
    return nullptr;
  }

  llvm::Error storeShard(llvm::StringRef ShardIdentifier,
                         IndexFileOut Shard) const override {
    vlog("Couldn't find project for {0}, indexing in-memory only",
         ShardIdentifier);
    return llvm::Error::success();
  }
};

// Creates and owns IndexStorages for multiple CDBs.
class DiskBackedIndexStorageManager {
public:
  DiskBackedIndexStorageManager()
      : IndexStorageMapMu(llvm::make_unique<std::mutex>()) {}

  // Creates or fetches to storage from cache for the specified CDB.
  BackgroundIndexStorage *operator()(llvm::StringRef CDBDirectory) {
    std::lock_guard<std::mutex> Lock(*IndexStorageMapMu);
    auto &IndexStorage = IndexStorageMap[CDBDirectory];
    if (!IndexStorage)
      IndexStorage = create(CDBDirectory);
    return IndexStorage.get();
  }

  // Creates or fetches to storage from cache for the specified CDB.
  BackgroundIndexStorage *createStorage(llvm::StringRef CDBDirectory);

private:
  std::unique_ptr<BackgroundIndexStorage> create(llvm::StringRef CDBDirectory) {
    if (CDBDirectory.empty())
      return llvm::make_unique<NullStorage>();
    return llvm::make_unique<DiskBackedIndexStorage>(CDBDirectory);
  }

  llvm::StringMap<std::unique_ptr<BackgroundIndexStorage>> IndexStorageMap;
  std::unique_ptr<std::mutex> IndexStorageMapMu;
};

} // namespace

BackgroundIndexStorage::Factory
BackgroundIndexStorage::createDiskBackedStorageFactory() {
  return DiskBackedIndexStorageManager();
}

} // namespace clangd
} // namespace clang