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      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 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 FileDescriptor is non-null, then this lookup should only return success
     38 /// for files (not directories).  If it is null 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.
     42 bool FileSystemStatCache::get(const char *Path, struct stat &StatBuf,
     43                               int *FileDescriptor, FileSystemStatCache *Cache) {
     44   LookupResult R;
     45   bool isForDir = FileDescriptor == 0;
     46 
     47   // If we have a cache, use it to resolve the stat query.
     48   if (Cache)
     49     R = Cache->getStat(Path, StatBuf, FileDescriptor);
     50   else if (isForDir) {
     51     // If this is a directory and we have no cache, just go to the file system.
     52     R = ::stat(Path, &StatBuf) != 0 ? CacheMissing : CacheExists;
     53   } else {
     54     // Otherwise, we have to go to the filesystem.  We can always just use
     55     // 'stat' here, but (for files) the client is asking whether the file exists
     56     // because it wants to turn around and *open* it.  It is more efficient to
     57     // do "open+fstat" on success than it is to do "stat+open".
     58     //
     59     // Because of this, check to see if the file exists with 'open'.  If the
     60     // open succeeds, use fstat to get the stat info.
     61     int OpenFlags = O_RDONLY;
     62 #ifdef O_BINARY
     63     OpenFlags |= O_BINARY;  // Open input file in binary mode on win32.
     64 #endif
     65     *FileDescriptor = ::open(Path, OpenFlags);
     66 
     67     if (*FileDescriptor == -1) {
     68       // If the open fails, our "stat" fails.
     69       R = CacheMissing;
     70     } else {
     71       // Otherwise, the open succeeded.  Do an fstat to get the information
     72       // about the file.  We'll end up returning the open file descriptor to the
     73       // client to do what they please with it.
     74       if (::fstat(*FileDescriptor, &StatBuf) == 0)
     75         R = CacheExists;
     76       else {
     77         // fstat rarely fails.  If it does, claim the initial open didn't
     78         // succeed.
     79         R = CacheMissing;
     80         ::close(*FileDescriptor);
     81         *FileDescriptor = -1;
     82       }
     83     }
     84   }
     85 
     86   // If the path doesn't exist, return failure.
     87   if (R == CacheMissing) return true;
     88 
     89   // If the path exists, make sure that its "directoryness" matches the clients
     90   // demands.
     91   if (S_ISDIR(StatBuf.st_mode) != isForDir) {
     92     // If not, close the file if opened.
     93     if (FileDescriptor && *FileDescriptor != -1) {
     94       ::close(*FileDescriptor);
     95       *FileDescriptor = -1;
     96     }
     97 
     98     return true;
     99   }
    100 
    101   return false;
    102 }
    103 
    104 
    105 MemorizeStatCalls::LookupResult
    106 MemorizeStatCalls::getStat(const char *Path, struct stat &StatBuf,
    107                            int *FileDescriptor) {
    108   LookupResult Result = statChained(Path, StatBuf, FileDescriptor);
    109 
    110   // Do not cache failed stats, it is easy to construct common inconsistent
    111   // situations if we do, and they are not important for PCH performance (which
    112   // currently only needs the stats to construct the initial FileManager
    113   // entries).
    114   if (Result == CacheMissing)
    115     return Result;
    116 
    117   // Cache file 'stat' results and directories with absolutely paths.
    118   if (!S_ISDIR(StatBuf.st_mode) || llvm::sys::path::is_absolute(Path))
    119     StatCalls[Path] = StatBuf;
    120 
    121   return Result;
    122 }
    123