Fix for the font files being maped multiple times (Fontconfig).

content/common/font_config_ipc_linux.cc

Index: content/common/font_config_ipc_linux.cc
diff --git a/content/common/font_config_ipc_linux.cc b/content/common/font_config_ipc_linux.cc
index c64aebf66a57fa3c432646d1906e5a15bf12b2ef..d4eaebfb7a17a78e5265f53e7974fb32dab2f3c8 100644
--- a/content/common/font_config_ipc_linux.cc
+++ b/content/common/font_config_ipc_linux.cc
@@ -14,8 +14,11 @@
 
 #include "base/debug/trace_event.h"
 #include "base/files/file_util.h"
+#include "base/files/memory_mapped_file.h"
+#include "base/memory/ref_counted.h"
 #include "base/pickle.h"
 #include "base/posix/unix_domain_socket_linux.h"
+#include "base/threading/thread_restrictions.h"
 #include "skia/ext/refptr.h"
 #include "skia/ext/skia_utils_base.h"
 #include "third_party/skia/include/core/SkData.h"
@@ -23,14 +26,45 @@
 
 namespace content {
 
-// Return a stream from the file descriptor, or NULL on failure.
-SkStream* StreamFromFD(int fd) {
-  skia::RefPtr<SkData> data = skia::AdoptRef(SkData::NewFromFD(fd));
-  if (!data) {
-    return NULL;
+class FontConfigIPC::MappedFontFile
+    : public base::RefCountedThreadSafe<MappedFontFile> {
+ public:
+  explicit MappedFontFile(uint32_t font_id) : font_id_(font_id) {}
+
+  uint32_t font_id() const { return font_id_; }
+
+  bool Initialize(int fd) {
+    base::ThreadRestrictions::ScopedAllowIO allow_mmap;
+    return mapped_font_file_.Initialize(base::File(fd));
+  }
+
+  SkMemoryStream* CreateMemoryStream() {
+    DCHECK(mapped_font_file_.IsValid());
+    auto data = skia::AdoptRef(SkData::NewWithProc(
+        mapped_font_file_.data(), mapped_font_file_.length(),
+        &MappedFontFile::ReleaseProc, this));
+    if (!data)
+      return nullptr;
+    AddRef();
+    return new SkMemoryStream(data.get());
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<MappedFontFile>;
+
+  ~MappedFontFile() {

[Daniel Erat, 2015/01/14 23:40:27]

as i understand it, you should be using 'override' on the d'tor whenever the
class derives from some other class

[Krzysztof Olczyk, 2015/01/15 09:05:28]

When it derives from base class which has virtual constructor. If I add override
here, I'm getting, unsurprisingly, the following error:

../../content/common/font_config_ipc_linux.cc:55:21: error: only virtual member
functions can be marked 'override'

[Daniel Erat, 2015/01/15 15:55:54]

ah, thanks; i didn't realize that RefCountedThreadSafe doesn't declare a virtual
d'tor. does 'virtual' work here?

(maybe none of this matters since this d'tor is private.)

[Krzysztof Olczyk, 2015/01/15 17:44:11]

It uses CRTP in order to match right destructor instead. 
I don't think we need a virtual destructor as this class is not going to be
inherited. 

+    auto font_config = static_cast<FontConfigIPC*>(FontConfigIPC::RefGlobal());
+    font_config->RemoveMappedFontFile(this);
   }
-  return new SkMemoryStream(data.get());
-}
+
+  static void ReleaseProc(const void* ptr, size_t length, void* context) {
+    base::ThreadRestrictions::ScopedAllowIO allow_munmap;
+    static_cast<MappedFontFile*>(context)->Release();
+  }
+
+  uint32_t font_id_;
+  base::MemoryMappedFile mapped_font_file_;
+};
 
 void CloseFD(int fd) {
   int err = IGNORE_EINTR(close(fd));
@@ -96,6 +130,14 @@ bool FontConfigIPC::matchFamilyName(const char familyName[],
 
 SkStream* FontConfigIPC::openStream(const FontIdentity& identity) {
   TRACE_EVENT0("sandbox_ipc", "FontConfigIPC::openStream");
+
+  {
+    base::AutoLock lock(stream_opening_lock_);
+    auto mapped_font_files_it = mapped_font_files_.find(identity.fID);
+    if (mapped_font_files_it != mapped_font_files_.end())
+      return mapped_font_files_it->second->CreateMemoryStream();
+  }
+
   Pickle request;
   request.WriteInt(METHOD_OPEN);
   request.WriteUInt32(identity.fID);
@@ -118,9 +160,23 @@ SkStream* FontConfigIPC::openStream(const FontIdentity& identity) {
     return NULL;
   }
 
-  SkStream* stream = StreamFromFD(result_fd);
-  CloseFD(result_fd);
-  return stream;
+  scoped_refptr<MappedFontFile> mapped_font_file =
+      new MappedFontFile(identity.fID);
+  if (!mapped_font_file->Initialize(result_fd))
+    return nullptr;
+
+  {
+    base::AutoLock lock(stream_opening_lock_);
+    auto mapped_font_files_it =
+        mapped_font_files_.insert(std::make_pair(mapped_font_file->font_id(),
+                                                 mapped_font_file.get())).first;
+    return mapped_font_files_it->second->CreateMemoryStream();
+  }
+}
+
+void FontConfigIPC::RemoveMappedFontFile(MappedFontFile* mapped_font_file) {
+  base::AutoLock lock(stream_opening_lock_);
+  mapped_font_files_.erase(mapped_font_file->font_id());
 }
 
 }  // namespace content