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
11 namespace clang {
12 namespace clangd {
13
14 // Sentinel values for the Size cache key. In both cases, a successful stat of
15 // the file will never result in the cached value being reused.
16
17 // The cached value does not reflect the current content on disk.
18 static constexpr uint64_t CacheDiskMismatch =
19 std::numeric_limits<uint64_t>::max();
20 // The cached value reflects that the file doesn't exist.
21 static constexpr uint64_t FileNotFound = CacheDiskMismatch - 1;
22
FileCache(llvm::StringRef Path)23 FileCache::FileCache(llvm::StringRef Path)
24 : Path(Path), ValidTime(std::chrono::steady_clock::time_point::min()),
25 ModifiedTime(), Size(CacheDiskMismatch) {
26 assert(llvm::sys::path::is_absolute(Path));
27 }
28
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) const29 void FileCache::read(
30 const ThreadsafeFS &TFS, std::chrono::steady_clock::time_point FreshTime,
31 llvm::function_ref<void(llvm::Optional<llvm::StringRef>)> Parse,
32 llvm::function_ref<void()> Read) const {
33
34 std::lock_guard<std::mutex> Lock(Mu);
35 // We're going to update the cache and return whatever's in it.
36 auto Return = llvm::make_scope_exit(Read);
37
38 // Return any sufficiently recent result without doing any further work.
39 if (ValidTime > FreshTime)
40 return;
41
42 // Ensure we always bump ValidTime, so that FreshTime imposes a hard limit on
43 // how often we do IO.
44 auto BumpValidTime = llvm::make_scope_exit(
45 [&] { ValidTime = std::chrono::steady_clock::now(); });
46
47 // stat is cheaper than opening the file. It's usually unchanged.
48 assert(llvm::sys::path::is_absolute(Path));
49 auto FS = TFS.view(/*CWD=*/llvm::None);
50 auto Stat = FS->status(Path);
51 if (!Stat || !Stat->isRegularFile()) {
52 if (Size != FileNotFound) // Allow "not found" value to be cached.
53 Parse(llvm::None);
54 // Ensure the cache key won't match any future stat().
55 Size = FileNotFound;
56 return;
57 }
58 // If the modified-time and size match, assume the content does too.
59 if (Size == Stat->getSize() &&
60 ModifiedTime == Stat->getLastModificationTime())
61 return;
62
63 // OK, the file has actually changed. Update cache key, compute new value.
64 Size = Stat->getSize();
65 ModifiedTime = Stat->getLastModificationTime();
66 // Now read the file from disk.
67 if (auto Buf = FS->getBufferForFile(Path)) {
68 Parse(Buf->get()->getBuffer());
69 // Result is cacheable if the actual read size matches the new cache key.
70 // (We can't update the cache key, because we don't know the new mtime).
71 if (Buf->get()->getBufferSize() != Size)
72 Size = CacheDiskMismatch;
73 } else {
74 // File was unreadable. Keep the old value and try again next time.
75 Size = CacheDiskMismatch;
76 }
77 }
78
79 } // namespace clangd
80 } // namespace clang
81