clang/lib/Basic/FileSystemStatCache.cpp

   1 //===- FileSystemStatCache.cpp - Caching for 'stat' calls -----------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 //  This file defines the FileSystemStatCache interface.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "clang/Basic/FileSystemStatCache.h"
  14 #include "llvm/Support/Chrono.h"
  15 #include "llvm/Support/ErrorOr.h"
  16 #include "llvm/Support/Path.h"
  17 #include "llvm/Support/VirtualFileSystem.h"
  18 #include <utility>
  19
  20 using namespace clang;
  21
  22 void FileSystemStatCache::anchor() {}
  23
  24 /// FileSystemStatCache::get - Get the 'stat' information for the specified
  25 /// path, using the cache to accelerate it if possible.  This returns true if
  26 /// the path does not exist or false if it exists.
  27 ///
  28 /// If isFile is true, then this lookup should only return success for files
  29 /// (not directories).  If it is false this lookup should only return
  30 /// success for directories (not files).  On a successful file lookup, the
  31 /// implementation can optionally fill in FileDescriptor with a valid
  32 /// descriptor and the client guarantees that it will close it.
  33 std::error_code
  34 FileSystemStatCache::get(StringRef Path, llvm::vfs::Status &Status,
  35                          bool isFile, std::unique_ptr<llvm::vfs::File> *F,
  36                          FileSystemStatCache *Cache,
  37                          llvm::vfs::FileSystem &FS) {
  38   bool isForDir = !isFile;
  39   std::error_code RetCode;
  40
  41   // If we have a cache, use it to resolve the stat query.
  42   if (Cache)
  43     RetCode = Cache->getStat(Path, Status, isFile, F, FS);
  44   else if (isForDir || !F) {
  45     // If this is a directory or a file descriptor is not needed and we have
  46     // no cache, just go to the file system.
  47     llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = FS.status(Path);
  48     if (!StatusOrErr) {
  49       RetCode = StatusOrErr.getError();
  50     } else {
  51       Status = *StatusOrErr;
  52     }
  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     auto OwnedFile = FS.openFileForRead(Path);
  62
  63     if (!OwnedFile) {
  64       // If the open fails, our "stat" fails.
  65       RetCode = OwnedFile.getError();
  66     } else {
  67       // Otherwise, the open succeeded.  Do an fstat to get the information
  68       // about the file.  We'll end up returning the open file descriptor to the
  69       // client to do what they please with it.
  70       llvm::ErrorOr<llvm::vfs::Status> StatusOrErr = (*OwnedFile)->status();
  71       if (StatusOrErr) {
  72         Status = *StatusOrErr;
  73         *F = std::move(*OwnedFile);
  74       } else {
  75         // fstat rarely fails.  If it does, claim the initial open didn't
  76         // succeed.
  77         *F = nullptr;
  78         RetCode = StatusOrErr.getError();
  79       }
  80     }
  81   }
  82
  83   // If the path doesn't exist, return failure.
  84   if (RetCode)
  85     return RetCode;
  86
  87   // If the path exists, make sure that its "directoryness" matches the clients
  88   // demands.
  89   if (Status.isDirectory() != isForDir) {
  90     // If not, close the file if opened.
  91     if (F)
  92       *F = nullptr;
  93     return std::make_error_code(
  94         Status.isDirectory() ?
  95             std::errc::is_a_directory : std::errc::not_a_directory);
  96   }
  97
  98   return std::error_code();
  99 }
 100
 101 std::error_code
 102 MemorizeStatCalls::getStat(StringRef Path, llvm::vfs::Status &Status,
 103                            bool isFile,
 104                            std::unique_ptr<llvm::vfs::File> *F,
 105                            llvm::vfs::FileSystem &FS) {
 106   auto err = get(Path, Status, isFile, F, nullptr, FS);
 107   if (err) {
 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
 110     // (which currently only needs the stats to construct the initial
 111     // FileManager entries).
 112     return err;
 113   }
 114
 115   // Cache file 'stat' results and directories with absolutely paths.
 116   if (!Status.isDirectory() || llvm::sys::path::is_absolute(Path))
 117     StatCalls[Path] = Status;
 118
 119   return std::error_code();
 120 }