[FileManager] Revert r347205 to avoid PCH file-descriptor leak.

[sammccall]

Summary

r347205 fixed a bug in FileManager: first calling
getFile(shouldOpen=false) and then getFile(shouldOpen=true) results in
the file not being open.

Unfortunately, some code was (inadvertently?) relying on this bug: when
building with a PCH, the file entries are obtained first by passing
shouldOpen=false, and then later shouldOpen=true, without any intention
of reading them. After r347205, they do get unneccesarily opened.
Aside from extra operations, this means they need to be closed. Normally
files are closed when their contents are read. As these files are never
read, they stay open until clang exits. On platforms with a low
open-files limit (e.g. Mac), this can lead to spurious file-not-found
errors when building large projects with PCH enabled, e.g.

https://bugs.chromium.org/p/chromium/issues/detail?id=924225

Fixing the callsites to pass shouldOpen=false when the file won't be
read is not quite trivial (that info isn't available at the direct
callsite), and passing shouldOpen=false is a performance regression (it
results in open+fstat pairs being replaced by stat+open).

So an ideal fix is going to be a little risky and we need some fix soon
(especially for the llvm 8 branch).
The problem addressed by r347205 is rare and has only been observed in
clangd. It was present in llvm-7, so we can live with it for now.

[thakis]

lib/Basic/FileManager.cpp

295

Should this call fillRealPathName() (which was added after your change)?

[thakis]

lgtm, but lebtm with call to fillRealPathName()

[sammccall]

avoid revert of fillRealPathName() (thanks Nico!)

[thakis]

A few weeks later, I realize that since the test doesn't have a ".test" extension, it doesn't run on any bots. Could you rename it to leakfiles.test (or any other fitting extension listed in clang/test/lit.cfg.py's config.suffixes list)?

[sammccall]

Renamed in rL368455

include/clang/Basic/FileManager.h

class FileEntry {
   off_t Size;                 // File size in bytes.
   time_t ModTime;             // Modification time of file.
   const DirectoryEntry *Dir;  // Directory file lives in.
   unsigned UID;               // A unique (small) ID for the file.
   llvm::sys::fs::UniqueID UniqueID;
   bool IsNamedPipe;
   bool InPCH;
   bool IsValid;               // Is this \c FileEntry initialized and valid?
-  bool DeferredOpen;          // Created by getFile(OpenFile=0); may open later.
 
   /// The open file, if it is owned by the \p FileEntry.
   mutable std::unique_ptr<llvm::vfs::File> File;
 
 public:
   FileEntry()
-      : UniqueID(0, 0), IsNamedPipe(false), InPCH(false), IsValid(false),
-        DeferredOpen(false) {}
+      : UniqueID(0, 0), IsNamedPipe(false), InPCH(false), IsValid(false)
+  {}
 
   FileEntry(const FileEntry &) = delete;
   FileEntry &operator=(const FileEntry &) = delete;
 
   StringRef getName() const { return Name; }
   StringRef tryGetRealPathName() const { return RealPathName; }
   bool isValid() const { return IsValid; }
   off_t getSize() const { return Size; }

lib/Basic/FileManager.cpp

const FileEntry *FileManager::getFile(StringRef Filename, bool openFile,
                                       bool CacheFailure) {
   ++NumFileLookups;
 
   // See if there is already an entry in the map.
   auto &NamedFileEnt =
       *SeenFileEntries.insert(std::make_pair(Filename, nullptr)).first;
 
   // See if there is already an entry in the map.
-  if (NamedFileEnt.second) {
-    if (NamedFileEnt.second == NON_EXISTENT_FILE)
-      return nullptr;
-    // Entry exists: return it *unless* it wasn't opened and open is requested.
-    if (!(NamedFileEnt.second->DeferredOpen && openFile))
-      return NamedFileEnt.second;
-    // We previously stat()ed the file, but didn't open it: do that below.
-    // FIXME: the below does other redundant work too (stats the dir and file).
-  } else {
-    // By default, initialize it to invalid.
-    NamedFileEnt.second = NON_EXISTENT_FILE;
-  }
+  if (NamedFileEnt.second)
+    return NamedFileEnt.second == NON_EXISTENT_FILE ? nullptr
+                                                    : NamedFileEnt.second;
 
   ++NumFileCacheMisses;
 
+  // By default, initialize it to invalid.
+  NamedFileEnt.second = NON_EXISTENT_FILE;
+
   // Get the null-terminated file name as stored as the key of the
   // SeenFileEntries map.
   StringRef InterndFileName = NamedFileEnt.first();
 
   // Look up the directory for the file.  When looking up something like
   // sys/foo.h we'll discover all of the search directories that have a 'sys'
   // subdirectory.  This will let us avoid having to waste time on known-to-fail
   // searches when we go to find sys/bar.h, because all the search directories
if (getStatValue(InterndFileName, Data, true, openFile ? &F : nullptr)) {
     return nullptr;
   }
 
   assert((openFile || !F) && "undesired open file");
 
   // It exists.  See if we have already opened a file with the same inode.
   // This occurs when one dir is symlinked to another, for example.
   FileEntry &UFE = UniqueRealFiles[Data.UniqueID];
-  UFE.DeferredOpen = !openFile;
 
   NamedFileEnt.second = &UFE;
 
   // If the name returned by getStatValue is different than Filename, re-intern
   // the name.
   if (Data.Name != Filename) {
     auto &NamedFileEnt =
         *SeenFileEntries.insert(std::make_pair(Data.Name, nullptr)).first;
     if (!NamedFileEnt.second)
       NamedFileEnt.second = &UFE;
     else
       assert(NamedFileEnt.second == &UFE &&
              "filename from getStatValue() refers to wrong file");
     InterndFileName = NamedFileEnt.first().data();
   }
 
-  // If we opened the file for the first time, record the resulting info.
-  // Do this even if the cache entry was valid, maybe we didn't previously open.
-  if (F && !UFE.File) {
-    if (auto PathName = F->getName())
-      fillRealPathName(&UFE, *PathName);
-    UFE.File = std::move(F);
-    assert(!UFE.DeferredOpen && "we just opened it!");
-  }
-
   if (UFE.isValid()) { // Already have an entry with this inode, return it.
 
     // FIXME: this hack ensures that if we look up a file by a virtual path in
     // the VFS that the getDir() will have the virtual path, even if we found
     // the file by a 'real' path first. This is required in order to find a
     // module's structure when its headers/module map are mapped in the VFS.
     // We should remove this as soon as we can properly support a file having
     // multiple names.
const FileEntry *FileManager::getFile(StringRef Filename, bool openFile,
   UFE.Name    = InterndFileName;
   UFE.Size = Data.Size;
   UFE.ModTime = Data.ModTime;
   UFE.Dir     = DirInfo;
   UFE.UID     = NextFileUID++;
   UFE.UniqueID = Data.UniqueID;
   UFE.IsNamedPipe = Data.IsNamedPipe;
   UFE.InPCH = Data.InPCH;
+  UFE.File = std::move(F);
   UFE.IsValid = true;
-  // Note File and DeferredOpen were initialized above.
 
+  if (UFE.File) {
+    if (auto PathName = UFE.File->getName())
+      fillRealPathName(&UFE, *PathName);
+  }
   return &UFE;
 }
 
 const FileEntry *
 FileManager::getVirtualFile(StringRef Filename, off_t Size,
                             time_t ModificationTime) {
   ++NumFileLookups;
 
   // See if there is already an entry in the map.
   auto &NamedFileEnt =
       *SeenFileEntries.insert(std::make_pair(Filename, nullptr)).first;
 
   // See if there is already an entry in the map.
   if (NamedFileEnt.second && NamedFileEnt.second != NON_EXISTENT_FILE)
FileManager::getVirtualFile(StringRef Filename, off_t Size,
 
   UFE->Name    = InterndFileName;
   UFE->Size    = Size;
   UFE->ModTime = ModificationTime;
   UFE->Dir     = DirInfo;
   UFE->UID     = NextFileUID++;
   UFE->IsValid = true;
   UFE->File.reset();
-  UFE->DeferredOpen = false;
   return UFE;
 }
 
 bool FileManager::FixupRelativePath(SmallVectorImpl<char> &path) const {
   StringRef pathRef(path.data(), path.size());
 
   if (FileSystemOpts.WorkingDir.empty()
       || llvm::sys::path::is_absolute(pathRef))

test/PCH/leakfiles

+// Test that compiling using a PCH doesn't leak file descriptors.
+// https://bugs.chromium.org/p/chromium/issues/detail?id=924225
+//
+// This test requires bash loops and ulimit.
+// REQUIRES: shell
+// UNSUPPORTED: win32
+//
+// Set up source files. lib/lib.h includes lots of lib*.h files in that dir.
+// client.c includes lib/lib.h, and also the individual files directly.
+//
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: cd %t
+// RUN: mkdir lib
+// RUN: for i in {1..300}; do touch lib/lib$i.h; done
+// RUN: for i in {1..300}; do echo "#include \"lib$i.h\"" >> lib/lib.h; done
+// RUN: echo "#include \"lib/lib.h\"" > client.c
+// RUN: for i in {1..300}; do echo "#include \"lib/lib$i.h\"" >> client.c; done
+//
+// We want to verify that we don't hold all the files open at the same time.
+// This is important e.g. on mac, which has a low default FD limit.
+// RUN: ulimit -n 100
+//
+// Test without PCH.
+// RUN: %clang_cc1 -fsyntax-only -Ilib/ client.c
+//
+// Test with PCH.
+// RUN: %clang_cc1 -emit-pch -o pch -Ilib/ client.c
+// RUN: %clang_cc1 -include-pch pch -Ilib/ client.c -fsyntax-only

unittests/Basic/FileManagerTest.cpp

TEST_F(FileManagerTest, getFileReturnsNULLForNonexistentFile) {
 
   // Create a virtual bar.cpp file.
   manager.getVirtualFile("bar.cpp", 200, 0);
 
   const FileEntry *file = manager.getFile("xyz.txt");
   EXPECT_EQ(nullptr, file);
 }
 
-// When calling getFile(OpenFile=false); getFile(OpenFile=true) the file is
-// opened for the second call.
-TEST_F(FileManagerTest, getFileDefersOpen) {
-  llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> FS(
-      new llvm::vfs::InMemoryFileSystem());
-  FS->addFile("/tmp/test", 0, llvm::MemoryBuffer::getMemBufferCopy("test"));
-  FS->addFile("/tmp/testv", 0, llvm::MemoryBuffer::getMemBufferCopy("testv"));
-  FileManager manager(options, FS);
-
-  const FileEntry *file = manager.getFile("/tmp/test", /*OpenFile=*/false);
-  ASSERT_TRUE(file != nullptr);
-  ASSERT_TRUE(file->isValid());
-  // "real path name" reveals whether the file was actually opened.
-  EXPECT_FALSE(file->isOpenForTests());
-
-  file = manager.getFile("/tmp/test", /*OpenFile=*/true);
-  ASSERT_TRUE(file != nullptr);
-  ASSERT_TRUE(file->isValid());
-  EXPECT_TRUE(file->isOpenForTests());
-
-  // However we should never try to open a file previously opened as virtual.
-  ASSERT_TRUE(manager.getVirtualFile("/tmp/testv", 5, 0));
-  ASSERT_TRUE(manager.getFile("/tmp/testv", /*OpenFile=*/false));
-  file = manager.getFile("/tmp/testv", /*OpenFile=*/true);
-  EXPECT_FALSE(file->isOpenForTests());
-}
-
 // The following tests apply to Unix-like system only.
 
 #ifndef _WIN32
 
 // getFile() returns the same FileEntry for real files that are aliases.
 TEST_F(FileManagerTest, getFileReturnsSameFileEntryForAliasedRealFiles) {
   // Inject two real files with the same inode.
   auto statCache = llvm::make_unique<FakeStatCache>();