83 lines · cpp
1//===--- FileCache.cpp ----------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "support/FileCache.h"10#include "llvm/ADT/ScopeExit.h"11#include <optional>12 13namespace clang {14namespace clangd {15 16// Sentinel values for the Size cache key. In both cases, a successful stat of17// the file will never result in the cached value being reused.18 19// The cached value does not reflect the current content on disk.20static constexpr uint64_t CacheDiskMismatch =21 std::numeric_limits<uint64_t>::max();22// The cached value reflects that the file doesn't exist.23static constexpr uint64_t FileNotFound = CacheDiskMismatch - 1;24 25FileCache::FileCache(llvm::StringRef Path)26 : Path(Path), ValidTime(std::chrono::steady_clock::time_point::min()),27 ModifiedTime(), Size(CacheDiskMismatch) {28 assert(llvm::sys::path::is_absolute(Path));29}30 31void FileCache::read(32 const ThreadsafeFS &TFS, std::chrono::steady_clock::time_point FreshTime,33 llvm::function_ref<void(std::optional<llvm::StringRef>)> Parse,34 llvm::function_ref<void()> Read) const {35 36 std::lock_guard<std::mutex> Lock(Mu);37 // We're going to update the cache and return whatever's in it.38 auto Return = llvm::make_scope_exit(Read);39 40 // Return any sufficiently recent result without doing any further work.41 if (ValidTime > FreshTime)42 return;43 44 // Ensure we always bump ValidTime, so that FreshTime imposes a hard limit on45 // how often we do IO.46 auto BumpValidTime = llvm::make_scope_exit(47 [&] { ValidTime = std::chrono::steady_clock::now(); });48 49 // stat is cheaper than opening the file. It's usually unchanged.50 assert(llvm::sys::path::is_absolute(Path));51 auto FS = TFS.view(/*CWD=*/std::nullopt);52 auto Stat = FS->status(Path);53 if (!Stat || !Stat->isRegularFile()) {54 if (Size != FileNotFound) // Allow "not found" value to be cached.55 Parse(std::nullopt);56 // Ensure the cache key won't match any future stat().57 Size = FileNotFound;58 return;59 }60 // If the modified-time and size match, assume the content does too.61 if (Size == Stat->getSize() &&62 ModifiedTime == Stat->getLastModificationTime())63 return;64 65 // OK, the file has actually changed. Update cache key, compute new value.66 Size = Stat->getSize();67 ModifiedTime = Stat->getLastModificationTime();68 // Now read the file from disk.69 if (auto Buf = FS->getBufferForFile(Path)) {70 Parse(Buf->get()->getBuffer());71 // Result is cacheable if the actual read size matches the new cache key.72 // (We can't update the cache key, because we don't know the new mtime).73 if (Buf->get()->getBufferSize() != Size)74 Size = CacheDiskMismatch;75 } else {76 // File was unreadable. Keep the old value and try again next time.77 Size = CacheDiskMismatch;78 }79}80 81} // namespace clangd82} // namespace clang83