[Bindings] Create and use V8 context snapshots

gin/v8_initializer.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gin/v8_initializer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 25 matching lines @@
 #include "base/path_service.h"
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
 namespace gin {
 
 namespace {
 
 // None of these globals are ever freed nor closed.
 base::MemoryMappedFile* g_mapped_natives = nullptr;
 base::MemoryMappedFile* g_mapped_snapshot = nullptr;
+base::MemoryMappedFile* g_mapped_context = nullptr;
+
+const char kV8ContextFileName[] = "context_blob.bin";

[Yuki, 2017/04/28 13:48:27]

kV8ContextSnapshotFilename?

[peria, 2017/06/01 08:33:31]

Done.

 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
 
 // File handles intentionally never closed. Not using File here because its
 // Windows implementation guards against two instances owning the same
 // PlatformFile (which we allow since we know it is never freed).
 typedef std::map<const char*,
                  std::pair<base::PlatformFile, base::MemoryMappedFile::Region>>
     OpenedFileMap;
 static base::LazyInstance<OpenedFileMap>::Leaky g_opened_files =
@@ skipping 325 matching lines @@
   base::debug::SetCrashKeyValue(kIgnitionEnabledKey,
                                 ignition_enabled_crash_key);
 
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
   v8::StartupData natives;
   natives.data = reinterpret_cast<const char*>(g_mapped_natives->data());
   natives.raw_size = static_cast<int>(g_mapped_natives->length());
   v8::V8::SetNativesDataBlob(&natives);
 
-  if (g_mapped_snapshot != NULL) {
+  if (g_mapped_snapshot) {
     v8::StartupData snapshot;
     snapshot.data = reinterpret_cast<const char*>(g_mapped_snapshot->data());
     snapshot.raw_size = static_cast<int>(g_mapped_snapshot->length());
     v8::V8::SetSnapshotDataBlob(&snapshot);
   }
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
   v8::V8::SetEntropySource(&GenerateEntropy);
   v8::V8::Initialize();
 
@@ skipping 15 matching lines @@
   if (g_mapped_snapshot) {
     *snapshot_data_out =
         reinterpret_cast<const char*>(g_mapped_snapshot->data());
     *snapshot_size_out = static_cast<int>(g_mapped_snapshot->length());
   } else {
     *snapshot_data_out = NULL;
     *snapshot_size_out = 0;
   }
 }
 
+// static
+void V8Initializer::LoadV8Context() {
+  if (g_mapped_context)
+    return;
+
+  OpenFileIfNecessary(kV8ContextFileName);
+  MapOpenedFile(GetOpenedFile(kV8ContextFileName), &g_mapped_context);
+}
+
+// static
+void V8Initializer::LoadV8ContextFromFD(base::PlatformFile snapshot_pf,
+                                        int64_t snapshot_offset,
+                                        int64_t snapshot_size) {
+  if (g_mapped_context)
+    return;
+
+  if (snapshot_pf == base::kInvalidPlatformFile)
+    return;

[Yuki, 2017/04/28 13:48:27]

Is it really okay to simply return?

Do we need to fallback to LoadV8Context()?
Or, should we crash?

If it's okay as is, then I'd like a comment about why.

[peria, 2017/06/01 08:33:31]

In this case, we fail to load the blob file.
Let's discuss the behavior in such a case.  IMO, I'd like to keep working even
without snapshot.

+
+  base::MemoryMappedFile::Region snapshot_region =
+      base::MemoryMappedFile::Region::kWholeFile;
+  if (snapshot_size != 0 || snapshot_offset != 0) {
+    snapshot_region.offset = snapshot_offset;
+    snapshot_region.size = snapshot_size;
+  }
+
+  LoadV8FileResult result = V8_LOAD_SUCCESS;
+  if (!MapV8File(snapshot_pf, snapshot_region, &g_mapped_context))
+    result = V8_LOAD_FAILED_MAP;
+  if (result == V8_LOAD_SUCCESS) {

[Yuki, 2017/04/28 13:48:27]

Why don't you simply write
  if (MapV8File(...)) { ... }
?

[peria, 2017/05/30 08:25:41]

Done.

+    g_opened_files.Get()[kV8ContextFileName] =
+        std::make_pair(snapshot_pf, snapshot_region);
+  }
+}
+
+// static
+base::PlatformFile V8Initializer::GetOpenV8ContextFileForChildProcesses(

[Yuki, 2017/04/28 13:48:27]

GetOpened?

I'm not sure what child processes are.  Are they renderer processes?  Then,
ForRendererProcesses is preferred.

[peria, 2017/05/30 08:25:41]

Acknowledged.

+    base::MemoryMappedFile::Region* region_out) {
+  const OpenedFileMap::mapped_type& opened =
+      OpenFileIfNecessary(kV8ContextFileName);
+  *region_out = opened.second;
+  return opened.first;
+}
+
+// static
+void V8Initializer::GetV8ContextData(const char** snapshot_data_out,
+                                     int* snapshot_size_out) {
+  if (g_mapped_context) {
+    *snapshot_data_out =
+        reinterpret_cast<const char*>(g_mapped_context->data());
+    *snapshot_size_out = static_cast<int>(g_mapped_context->length());
+  } else {
+    *snapshot_data_out = nullptr;
+    *snapshot_size_out = 0;
+  }
+}
+
+#if defined(OS_ANDROID)
+// static
+base::FilePath V8Initializer::GetV8ContextFilePath() {
+  base::FilePath path;
+  GetV8FilePath(kV8ContextFileName, &path);
+  return path;
+}
+#endif  // defined(OS_ANDROID)
+
 }  // namespace gin