FileSystemStatCache.cpp revision e5d30e3b403539b10aaa52f03875a2243bf88904 
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
31void 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.
42bool 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
107MemorizeStatCalls::LookupResult
108MemorizeStatCalls::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