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 
20 using namespace clang;
21 
22 void 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.
33 bool FileSystemStatCache::get(StringRef Path, llvm::vfs::Status &Status,
34                               bool isFile,
35                               std::unique_ptr<llvm::vfs::File> *F,
36                               FileSystemStatCache *Cache,
37                               llvm::vfs::FileSystem &FS) {
38   LookupResult R;
39   bool isForDir = !isFile;
40 
41   // If we have a cache, use it to resolve the stat query.
42   if (Cache)
43     R = 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       R = CacheMissing;
50     } else {
51       R = CacheExists;
52       Status = *StatusOrErr;
53     }
54   } else {
55     // Otherwise, we have to go to the filesystem.  We can always just use
56     // 'stat' here, but (for files) the client is asking whether the file exists
57     // because it wants to turn around and *open* it.  It is more efficient to
58     // do "open+fstat" on success than it is to do "stat+open".
59     //
60     // Because of this, check to see if the file exists with 'open'.  If the
61     // open succeeds, use fstat to get the stat info.
62     auto OwnedFile = FS.openFileForRead(Path);
63 
64     if (!OwnedFile) {
65       // If the open fails, our "stat" fails.
66       R = CacheMissing;
67     } else {
68       // Otherwise, the open succeeded.  Do an fstat to get the information
69       // about the file.  We'll end up returning the open file descriptor to the
70       // client to do what they please with it.
71       llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = (*OwnedFile)->status();
72       if (StatusOrErr) {
73         R = CacheExists;
74         Status = *StatusOrErr;
75         *F = std::move(*OwnedFile);
76       } else {
77         // fstat rarely fails.  If it does, claim the initial open didn't
78         // succeed.
79         R = CacheMissing;
80         *F = nullptr;
81       }
82     }
83   }
84 
85   // If the path doesn't exist, return failure.
86   if (R == CacheMissing) return true;
87 
88   // If the path exists, make sure that its "directoryness" matches the clients
89   // demands.
90   if (Status.isDirectory() != isForDir) {
91     // If not, close the file if opened.
92     if (F)
93       *F = nullptr;
94 
95     return true;
96   }
97 
98   return false;
99 }
100 
101 MemorizeStatCalls::LookupResult
102 MemorizeStatCalls::getStat(StringRef Path, llvm::vfs::Status &Status,
103                            bool isFile,
104                            std::unique_ptr<llvm::vfs::File> *F,
105                            llvm::vfs::FileSystem &FS) {
106   if (get(Path, Status, isFile, F, nullptr, FS)) {
107     // Do not cache failed stats, it is easy to construct common inconsistent
108     // situations if we do, and they are not important for PCH performance
109     // (which currently only needs the stats to construct the initial
110     // FileManager entries).
111     return CacheMissing;
112   }
113 
114   // Cache file 'stat' results and directories with absolutely paths.
115   if (!Status.isDirectory() || llvm::sys::path::is_absolute(Path))
116     StatCalls[Path] = Status;
117 
118   return CacheExists;
119 }
120