1//===- FileSystemStatCache.cpp - Caching for 'stat' calls -----------------===//
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//  This file defines the FileSystemStatCache interface.
10//
11//===----------------------------------------------------------------------===//
12
13#include "clang/Basic/FileSystemStatCache.h"
14#include "llvm/Support/Chrono.h"
15#include "llvm/Support/ErrorOr.h"
16#include "llvm/Support/Path.h"
17#include "llvm/Support/VirtualFileSystem.h"
18#include <utility>
19
20using namespace clang;
21
22void FileSystemStatCache::anchor() {}
23
24/// FileSystemStatCache::get - Get the 'stat' information for the specified
25/// path, using the cache to accelerate it if possible.  This returns true if
26/// the path does not exist or false if it exists.
27///
28/// If isFile is true, then this lookup should only return success for files
29/// (not directories).  If it is false this lookup should only return
30/// success for directories (not files).  On a successful file lookup, the
31/// implementation can optionally fill in FileDescriptor with a valid
32/// descriptor and the client guarantees that it will close it.
33std::error_code
34FileSystemStatCache::get(StringRef Path, llvm::vfs::Status &Status,
35                         bool isFile, std::unique_ptr<llvm::vfs::File> *F,
36                         FileSystemStatCache *Cache,
37                         llvm::vfs::FileSystem &FS) {
38  bool isForDir = !isFile;
39  std::error_code RetCode;
40
41  // If we have a cache, use it to resolve the stat query.
42  if (Cache)
43    RetCode = Cache->getStat(Path, Status, isFile, F, FS);
44  else if (isForDir || !F) {
45    // If this is a directory or a file descriptor is not needed and we have
46    // no cache, just go to the file system.
47    llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = FS.status(Path);
48    if (!StatusOrErr) {
49      RetCode = StatusOrErr.getError();
50    } else {
51      Status = *StatusOrErr;
52    }
53  } else {
54    // Otherwise, we have to go to the filesystem.  We can always just use
55    // 'stat' here, but (for files) the client is asking whether the file exists
56    // because it wants to turn around and *open* it.  It is more efficient to
57    // do "open+fstat" on success than it is to do "stat+open".
58    //
59    // Because of this, check to see if the file exists with 'open'.  If the
60    // open succeeds, use fstat to get the stat info.
61    auto OwnedFile = FS.openFileForRead(Path);
62
63    if (!OwnedFile) {
64      // If the open fails, our "stat" fails.
65      RetCode = OwnedFile.getError();
66    } else {
67      // Otherwise, the open succeeded.  Do an fstat to get the information
68      // about the file.  We'll end up returning the open file descriptor to the
69      // client to do what they please with it.
70      llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = (*OwnedFile)->status();
71      if (StatusOrErr) {
72        Status = *StatusOrErr;
73        *F = std::move(*OwnedFile);
74      } else {
75        // fstat rarely fails.  If it does, claim the initial open didn't
76        // succeed.
77        *F = nullptr;
78        RetCode = StatusOrErr.getError();
79      }
80    }
81  }
82
83  // If the path doesn't exist, return failure.
84  if (RetCode)
85    return RetCode;
86
87  // If the path exists, make sure that its "directoryness" matches the clients
88  // demands.
89  if (Status.isDirectory() != isForDir) {
90    // If not, close the file if opened.
91    if (F)
92      *F = nullptr;
93    return std::make_error_code(
94        Status.isDirectory() ?
95            std::errc::is_a_directory : std::errc::not_a_directory);
96  }
97
98  return std::error_code();
99}
100
101std::error_code
102MemorizeStatCalls::getStat(StringRef Path, llvm::vfs::Status &Status,
103                           bool isFile,
104                           std::unique_ptr<llvm::vfs::File> *F,
105                           llvm::vfs::FileSystem &FS) {
106  auto err = get(Path, Status, isFile, F, nullptr, FS);
107  if (err) {
108    // Do not cache failed stats, it is easy to construct common inconsistent
109    // situations if we do, and they are not important for PCH performance
110    // (which currently only needs the stats to construct the initial
111    // FileManager entries).
112    return err;
113  }
114
115  // Cache file 'stat' results and directories with absolutely paths.
116  if (!Status.isDirectory() || llvm::sys::path::is_absolute(Path))
117    StatCalls[Path] = Status;
118
119  return std::error_code();
120}
121