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//===- DependencyScanningFilesystem.h - clang-scan-deps fs ===---*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "clang/Basic/LLVM.h"
#include "clang/Lex/PreprocessorExcludedConditionalDirectiveSkipMapping.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/VirtualFileSystem.h"
#include <mutex>
namespace clang {
namespace tooling {
namespace dependencies {
/// An in-memory representation of a file system entity that is of interest to
/// the dependency scanning filesystem.
/// It represents one of the following:
/// - an opened source file with minimized contents and a stat value.
/// - an opened source file with original contents and a stat value.
/// - a directory entry with its stat value.
/// - an error value to represent a file system error.
/// - a placeholder with an invalid stat indicating a not yet initialized entry.
class CachedFileSystemEntry {
/// Default constructor creates an entry with an invalid stat.
CachedFileSystemEntry() : MaybeStat(llvm::vfs::Status()) {}
CachedFileSystemEntry(std::error_code Error) : MaybeStat(std::move(Error)) {}
/// Create an entry that represents an opened source file with minimized or
/// original contents.
/// The filesystem opens the file even for `stat` calls open to avoid the
/// issues with stat + open of minimized files that might lead to a
/// mismatching size of the file. If file is not minimized, the full file is
/// read and copied into memory to ensure that it's not memory mapped to avoid
/// running out of file descriptors.
static CachedFileSystemEntry createFileEntry(StringRef Filename,
llvm::vfs::FileSystem &FS,
bool Minimize = true);
/// Create an entry that represents a directory on the filesystem.
static CachedFileSystemEntry createDirectoryEntry(llvm::vfs::Status &&Stat);
/// \returns True if the entry is valid.
bool isValid() const { return !MaybeStat || MaybeStat->isStatusKnown(); }
/// \returns True if the current entry points to a directory.
bool isDirectory() const { return MaybeStat && MaybeStat->isDirectory(); }
/// \returns The error or the file's contents.
llvm::ErrorOr<StringRef> getContents() const {
if (!MaybeStat)
return MaybeStat.getError();
assert(!MaybeStat->isDirectory() && "not a file");
assert(isValid() && "not initialized");
return StringRef(Contents);
/// \returns The error or the status of the entry.
llvm::ErrorOr<llvm::vfs::Status> getStatus() const {
assert(isValid() && "not initialized");
return MaybeStat;
/// \returns the name of the file.
StringRef getName() const {
assert(isValid() && "not initialized");
return MaybeStat->getName();
/// Return the mapping between location -> distance that is used to speed up
/// the block skipping in the preprocessor.
const PreprocessorSkippedRangeMapping &getPPSkippedRangeMapping() const {
return PPSkippedRangeMapping;
CachedFileSystemEntry(CachedFileSystemEntry &&) = default;
CachedFileSystemEntry &operator=(CachedFileSystemEntry &&) = default;
CachedFileSystemEntry(const CachedFileSystemEntry &) = delete;
CachedFileSystemEntry &operator=(const CachedFileSystemEntry &) = delete;
llvm::ErrorOr<llvm::vfs::Status> MaybeStat;
// Store the contents in a small string to allow a
// move from the small string for the minimized contents.
// Note: small size of 1 allows us to store an empty string with an implicit
// null terminator without any allocations.
llvm::SmallString<1> Contents;
PreprocessorSkippedRangeMapping PPSkippedRangeMapping;
/// This class is a shared cache, that caches the 'stat' and 'open' calls to the
/// underlying real file system.
/// It is sharded based on the hash of the key to reduce the lock contention for
/// the worker threads.
class DependencyScanningFilesystemSharedCache {
struct SharedFileSystemEntry {
std::mutex ValueLock;
CachedFileSystemEntry Value;
/// Returns a cache entry for the corresponding key.
/// A new cache entry is created if the key is not in the cache. This is a
/// thread safe call.
SharedFileSystemEntry &get(StringRef Key);
struct CacheShard {
std::mutex CacheLock;
llvm::StringMap<SharedFileSystemEntry, llvm::BumpPtrAllocator> Cache;
std::unique_ptr<CacheShard[]> CacheShards;
unsigned NumShards;
/// A virtual file system optimized for the dependency discovery.
/// It is primarily designed to work with source files whose contents was was
/// preprocessed to remove any tokens that are unlikely to affect the dependency
/// computation.
/// This is not a thread safe VFS. A single instance is meant to be used only in
/// one thread. Multiple instances are allowed to service multiple threads
/// running in parallel.
class DependencyScanningWorkerFilesystem : public llvm::vfs::ProxyFileSystem {
DependencyScanningFilesystemSharedCache &SharedCache,
IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS,
ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings)
: ProxyFileSystem(std::move(FS)), SharedCache(SharedCache),
PPSkipMappings(PPSkipMappings) {}
llvm::ErrorOr<llvm::vfs::Status> status(const Twine &Path) override;
openFileForRead(const Twine &Path) override;
/// The set of files that should not be minimized.
llvm::StringSet<> IgnoredFiles;
void setCachedEntry(StringRef Filename, const CachedFileSystemEntry *Entry) {
bool IsInserted = Cache.try_emplace(Filename, Entry).second;
assert(IsInserted && "local cache is updated more than once");
const CachedFileSystemEntry *getCachedEntry(StringRef Filename) {
auto It = Cache.find(Filename);
return It == Cache.end() ? nullptr : It->getValue();
llvm::ErrorOr<const CachedFileSystemEntry *>
getOrCreateFileSystemEntry(const StringRef Filename);
DependencyScanningFilesystemSharedCache &SharedCache;
/// The local cache is used by the worker thread to cache file system queries
/// locally instead of querying the global cache every time.
llvm::StringMap<const CachedFileSystemEntry *, llvm::BumpPtrAllocator> Cache;
/// The optional mapping structure which records information about the
/// excluded conditional directive skip mappings that are used by the
/// currently active preprocessor.
ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings;
} // end namespace dependencies
} // end namespace tooling
} // end namespace clang