lib/Basic/FileSystemStatCache.cpp

   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
  31 /// FileSystemStatCache::get - Get the 'stat' information for the specified
  32 /// path, using the cache to accelerate 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.
  40 bool 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
 103 MemorizeStatCalls::LookupResult
 104 MemorizeStatCalls::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::is_absolute(Path))
 117     StatCalls[Path] = StatBuf;
 118
 119   return Result;
 120 }