1 //===--- FileSystemStatCache.cpp - Caching for 'stat' calls ---------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the FileSystemStatCache interface.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/Basic/FileSystemStatCache.h"
15 #include "llvm/Support/Path.h"
16 #include <fcntl.h>
17
18 // FIXME: This is terrible, we need this for ::close.
19 #if !defined(_MSC_VER) && !defined(__MINGW32__)
20 #include <unistd.h>
21 #include <sys/uio.h>
22 #else
23 #include <io.h>
24 #endif
25 using namespace clang;
26
27 #if defined(_MSC_VER)
28 #define S_ISDIR(s) ((_S_IFDIR & s) !=0)
29 #endif
30
anchor()31 void FileSystemStatCache::anchor() { }
32
33 /// FileSystemStatCache::get - Get the 'stat' information for the specified
34 /// path, using the cache to accelerate it if possible. This returns true if
35 /// the path does not exist or false if it exists.
36 ///
37 /// If isFile is true, then this lookup should only return success for files
38 /// (not directories). If it is false this lookup should only return
39 /// success for directories (not files). On a successful file lookup, the
40 /// implementation can optionally fill in FileDescriptor with a valid
41 /// descriptor and the client guarantees that it will close it.
get(const char * Path,struct stat & StatBuf,bool isFile,int * FileDescriptor,FileSystemStatCache * Cache)42 bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
43 bool isFile, int *FileDescriptor,
44 FileSystemStatCache *Cache) {
45 LookupResult R;
46 bool isForDir = !isFile;
47
48 // If we have a cache, use it to resolve the stat query.
49 if (Cache)
50 R = Cache->getStat(Path, StatBuf, isFile, FileDescriptor);
51 else if (isForDir || !FileDescriptor) {
52 // If this is a directory or a file descriptor is not needed and we have
53 // no cache, just go to the file system.
54 R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
55 } else {
56 // Otherwise, we have to go to the filesystem. We can always just use
57 // 'stat' here, but (for files) the client is asking whether the file exists
58 // because it wants to turn around and *open* it. It is more efficient to
59 // do "open+fstat" on success than it is to do "stat+open".
60 //
61 // Because of this, check to see if the file exists with 'open'. If the
62 // open succeeds, use fstat to get the stat info.
63 int OpenFlags = O_RDONLY;
64 #ifdef O_BINARY
65 OpenFlags |= O_BINARY; // Open input file in binary mode on win32.
66 #endif
67 *FileDescriptor = ::open(Path, OpenFlags);
68
69 if (*FileDescriptor == -1) {
70 // If the open fails, our "stat" fails.
71 R = CacheMissing;
72 } else {
73 // Otherwise, the open succeeded. Do an fstat to get the information
74 // about the file. We'll end up returning the open file descriptor to the
75 // client to do what they please with it.
76 if (::fstat(*FileDescriptor, &StatBuf) == 0)
77 R = CacheExists;
78 else {
79 // fstat rarely fails. If it does, claim the initial open didn't
80 // succeed.
81 R = CacheMissing;
82 ::close(*FileDescriptor);
83 *FileDescriptor = -1;
84 }
85 }
86 }
87
88 // If the path doesn't exist, return failure.
89 if (R == CacheMissing) return true;
90
91 // If the path exists, make sure that its "directoryness" matches the clients
92 // demands.
93 if (S_ISDIR(StatBuf.st_mode) != isForDir) {
94 // If not, close the file if opened.
95 if (FileDescriptor && *FileDescriptor != -1) {
96 ::close(*FileDescriptor);
97 *FileDescriptor = -1;
98 }
99
100 return true;
101 }
102
103 return false;
104 }
105
106
107 MemorizeStatCalls::LookupResult
getStat(const char * Path,struct stat & StatBuf,bool isFile,int * FileDescriptor)108 MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf,
109 bool isFile, int *FileDescriptor) {
110 LookupResult Result = statChained(Path, StatBuf, isFile, FileDescriptor);
111
112 // Do not cache failed stats, it is easy to construct common inconsistent
113 // situations if we do, and they are not important for PCH performance (which
114 // currently only needs the stats to construct the initial FileManager
115 // entries).
116 if (Result == CacheMissing)
117 return Result;
118
119 // Cache file 'stat' results and directories with absolutely paths.
120 if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::path::is_absolute(Path))
121 StatCalls[Path] = StatBuf;
122
123 return Result;
124 }
125