Infrastructure for reading V8's initial snapshot from external files

gin/isolate_holder.cc

Index: gin/isolate_holder.cc
diff --git a/gin/isolate_holder.cc b/gin/isolate_holder.cc
index 740e13640a0ab40ebbc35df043906e96f8904b1e..334c0e0ee5130c6e1c081cb40c9f0541b06a2da9 100644
--- a/gin/isolate_holder.cc
+++ b/gin/isolate_holder.cc
@@ -18,6 +18,11 @@
 #include "gin/public/v8_platform.h"
 #include "gin/run_microtasks_observer.h"
 
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+#include "base/files/memory_mapped_file.h"
+#include "base/path_service.h"
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+
 namespace gin {
 
 namespace {
@@ -29,8 +34,70 @@ bool GenerateEntropy(unsigned char* buffer, size_t amount) {
   return true;
 }
 
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+base::MemoryMappedFile* g_mapped_natives = NULL;
+base::MemoryMappedFile* g_mapped_snapshot = NULL;
+
+bool MapV8Files(base::FilePath* natives_path, base::FilePath* snapshot_path,
+                int natives_fd = -1, int snapshot_fd = -1) {
+  int flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
+
+  g_mapped_natives = new base::MemoryMappedFile;
+  if (!g_mapped_natives->IsValid()) {
+    if (natives_fd == -1
+        ? !g_mapped_natives->Initialize(base::File(*natives_path, flags))
+        : !g_mapped_natives->Initialize(base::File(natives_fd))) {
+      delete g_mapped_natives;
+      g_mapped_natives = NULL;
+      LOG(FATAL) << "Couldn't mmap v8 natives data file";
+      return false;
+    }
+  }
+
+  g_mapped_snapshot = new base::MemoryMappedFile;
+  if (!g_mapped_snapshot->IsValid()) {
+    if (snapshot_fd == -1
+        ? !g_mapped_snapshot->Initialize(base::File(*snapshot_path, flags))
+        : !g_mapped_snapshot->Initialize(base::File(snapshot_fd))) {
+      delete g_mapped_snapshot;
+      g_mapped_snapshot = NULL;
+      LOG(ERROR) << "Couldn't mmap v8 snapshot data file";
+      return false;
+    }
+  }
+
+  return true;
+}
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+
 }  // namespace
 
+
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+// static
+bool IsolateHolder::LoadV8Snapshot() {
+  if (g_mapped_natives && g_mapped_snapshot)
+    return true;
+
+  base::FilePath data_path;
+  PathService::Get(base::DIR_ANDROID_APP_DATA, &data_path);
+  DCHECK(!data_path.empty());
+
+  base::FilePath natives_path = data_path.AppendASCII("natives_blob.bin");
+  base::FilePath snapshot_path = data_path.AppendASCII("snapshot_blob.bin");
+
+  return MapV8Files(&natives_path, &snapshot_path);
+}
+
+//static
+bool IsolateHolder::LoadV8SnapshotFD(int natives_fd, int snapshot_fd) {
+  if (g_mapped_natives && g_mapped_snapshot)
+    return true;
+
+  return MapV8Files(NULL, NULL, natives_fd, snapshot_fd);
+}
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+
 IsolateHolder::IsolateHolder() {
   CHECK(g_array_buffer_allocator)
       << "You need to invoke gin::IsolateHolder::Initialize first";
@@ -88,6 +155,19 @@ void IsolateHolder::Initialize(ScriptMode mode,
     v8::V8::SetFlagsFromString(v8_flags, sizeof(v8_flags) - 1);
   }
   v8::V8::SetEntropySource(&GenerateEntropy);
+#ifdef V8_USE_EXTERNAL_STARTUP_DATA
+  v8::StartupData natives;
+  natives.data = reinterpret_cast<const char*>(g_mapped_natives->data());
+  natives.raw_size = g_mapped_natives->length();
+  natives.compressed_size = g_mapped_natives->length();
+  v8::V8::SetNativesDataBlob(&natives);
+
+  v8::StartupData snapshot;
+  snapshot.data = reinterpret_cast<const char*>(g_mapped_snapshot->data());
+  snapshot.raw_size = g_mapped_snapshot->length();
+  snapshot.compressed_size = g_mapped_snapshot->length();
+  v8::V8::SetSnapshotDataBlob(&snapshot);
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
   v8::V8::Initialize();
   v8_is_initialized = true;
 }