FileSystemStatCache.cpp revision 03013fa9a0bf1ef4b907f5fec006c8f4000fdd21 
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
25using namespace clang;
26
27#if defined(_MSC_VER)
28#define S_ISDIR(s) ((_S_IFDIR & s) !=0)
29#endif
30
31/// FileSystemStatCache::get - Get the 'stat' information for the specified
32/// path, using the cache to accellerate it if possible.  This returns true if
33/// the path does not exist or false if it exists.
34///
35/// If FileDescriptor is non-null, then this lookup should only return success
36/// for files (not directories).  If it is null this lookup should only return
37/// success for directories (not files).  On a successful file lookup, the
38/// implementation can optionally fill in FileDescriptor with a valid
39/// descriptor and the client guarantees that it will close it.
40bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
41                              int *FileDescriptor, FileSystemStatCache *Cache) {
42  LookupResult R;
43  bool isForDir = FileDescriptor == 0;
44
45  // If we have a cache, use it to resolve the stat query.
46  if (Cache)
47    R = Cache->getStat(Path, StatBuf, FileDescriptor);
48  else if (isForDir) {
49    // If this is a directory and we have no cache, just go to the file system.
50    R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
51  } else {
52    // Otherwise, we have to go to the filesystem.  We can always just use
53    // 'stat' here, but (for files) the client is asking whether the file exists
54    // because it wants to turn around and *open* it.  It is more efficient to
55    // do "open+fstat" on success than it is to do "stat+open".
56    //
57    // Because of this, check to see if the file exists with 'open'.  If the
58    // open succeeds, use fstat to get the stat info.
59    int OpenFlags = O_RDONLY;
60#ifdef O_BINARY
61    OpenFlags |= O_BINARY;  // Open input file in binary mode on win32.
62#endif
63    *FileDescriptor = ::open(Path, OpenFlags);
64
65    if (*FileDescriptor == -1) {
66      // If the open fails, our "stat" fails.
67      R = CacheMissing;
68    } else {
69      // Otherwise, the open succeeded.  Do an fstat to get the information
70      // about the file.  We'll end up returning the open file descriptor to the
71      // client to do what they please with it.
72      if (::fstat(*FileDescriptor, &StatBuf) == 0)
73        R = CacheExists;
74      else {
75        // fstat rarely fails.  If it does, claim the initial open didn't
76        // succeed.
77        R = CacheMissing;
78        ::close(*FileDescriptor);
79        *FileDescriptor = -1;
80      }
81    }
82  }
83
84  // If the path doesn't exist, return failure.
85  if (R == CacheMissing) return true;
86
87  // If the path exists, make sure that its "directoryness" matches the clients
88  // demands.
89  if (S_ISDIR(StatBuf.st_mode) != isForDir) {
90    // If not, close the file if opened.
91    if (FileDescriptor && *FileDescriptor != -1) {
92      ::close(*FileDescriptor);
93      *FileDescriptor = -1;
94    }
95
96    return true;
97  }
98
99  return false;
100}
101
102
103MemorizeStatCalls::LookupResult
104MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf,
105                           int *FileDescriptor) {
106  LookupResult Result = statChained(Path, StatBuf, FileDescriptor);
107
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 (which
110  // currently only needs the stats to construct the initial FileManager
111  // entries).
112  if (Result == CacheMissing)
113    return Result;
114
115  // Cache file 'stat' results and directories with absolutely paths.
116  if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::Path(Path).isAbsolute())
117    StatCalls[Path] = StatBuf;
118
119  return Result;
120}
121