clang-tools  15.0.0git
FileCache.cpp
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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-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "support/FileCache.h"
10 #include "llvm/ADT/ScopeExit.h"
11 
12 namespace clang {
13 namespace clangd {
14 
15 // Sentinel values for the Size cache key. In both cases, a successful stat of
16 // the file will never result in the cached value being reused.
17 
18 // The cached value does not reflect the current content on disk.
19 static constexpr uint64_t CacheDiskMismatch =
20  std::numeric_limits<uint64_t>::max();
21 // The cached value reflects that the file doesn't exist.
22 static constexpr uint64_t FileNotFound = CacheDiskMismatch - 1;
23 
24 FileCache::FileCache(llvm::StringRef Path)
25  : Path(Path), ValidTime(std::chrono::steady_clock::time_point::min()),
26  ModifiedTime(), Size(CacheDiskMismatch) {
27  assert(llvm::sys::path::is_absolute(Path));
28 }
29 
31  const ThreadsafeFS &TFS, std::chrono::steady_clock::time_point FreshTime,
32  llvm::function_ref<void(llvm::Optional<llvm::StringRef>)> Parse,
33  llvm::function_ref<void()> Read) const {
34 
35  std::lock_guard<std::mutex> Lock(Mu);
36  // We're going to update the cache and return whatever's in it.
37  auto Return = llvm::make_scope_exit(Read);
38 
39  // Return any sufficiently recent result without doing any further work.
40  if (ValidTime > FreshTime)
41  return;
42 
43  // Ensure we always bump ValidTime, so that FreshTime imposes a hard limit on
44  // how often we do IO.
45  auto BumpValidTime = llvm::make_scope_exit(
46  [&] { ValidTime = std::chrono::steady_clock::now(); });
47 
48  // stat is cheaper than opening the file. It's usually unchanged.
49  assert(llvm::sys::path::is_absolute(Path));
50  auto FS = TFS.view(/*CWD=*/llvm::None);
51  auto Stat = FS->status(Path);
52  if (!Stat || !Stat->isRegularFile()) {
53  if (Size != FileNotFound) // Allow "not found" value to be cached.
54  Parse(llvm::None);
55  // Ensure the cache key won't match any future stat().
56  Size = FileNotFound;
57  return;
58  }
59  // If the modified-time and size match, assume the content does too.
60  if (Size == Stat->getSize() &&
61  ModifiedTime == Stat->getLastModificationTime())
62  return;
63 
64  // OK, the file has actually changed. Update cache key, compute new value.
65  Size = Stat->getSize();
66  ModifiedTime = Stat->getLastModificationTime();
67  // Now read the file from disk.
68  if (auto Buf = FS->getBufferForFile(Path)) {
69  Parse(Buf->get()->getBuffer());
70  // Result is cacheable if the actual read size matches the new cache key.
71  // (We can't update the cache key, because we don't know the new mtime).
72  if (Buf->get()->getBufferSize() != Size)
73  Size = CacheDiskMismatch;
74  } else {
75  // File was unreadable. Keep the old value and try again next time.
76  Size = CacheDiskMismatch;
77  }
78 }
79 
80 } // namespace clangd
81 } // namespace clang
clang::clangd::Path
std::string Path
A typedef to represent a file path.
Definition: Path.h:26
FileCache.h
clang::clangd::FileNotFound
static constexpr uint64_t FileNotFound
Definition: FileCache.cpp:22
clang::clangd::ThreadsafeFS
Wrapper for vfs::FileSystem for use in multithreaded programs like clangd.
Definition: ThreadsafeFS.h:27
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
clang::clangd::DocumentHighlightKind::Read
@ Read
clang::clangd::FileCache::read
void read(const ThreadsafeFS &TFS, std::chrono::steady_clock::time_point FreshTime, llvm::function_ref< void(llvm::Optional< llvm::StringRef >)> Parse, llvm::function_ref< void()> Read) const
Definition: FileCache.cpp:30
clang::clangd::CacheDiskMismatch
static constexpr uint64_t CacheDiskMismatch
Definition: FileCache.cpp:19
clang::clangd::FileCache::FileCache
FileCache(PathRef Path)
Definition: FileCache.cpp:24