src: notify V8 for low memory when alloc fails

Call `v8::Isolate::GetCurrent()->LowMemoryNotification()` when
an allocation fails to give V8 a chance to clean up and return
memory before retrying (and possibly giving up).

PR-URL: nodejs#8482
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>

src/node.cc

@@ -198,6 +198,7 @@ bool trace_warnings = false;
 // that is used by lib/module.js
 bool config_preserve_symlinks = false;
 
+bool v8_initialized = false;
 
 // Set in node.cc by ParseArgs when --expose-internals or --expose_internals is
 // used.
@@ -4895,6 +4896,7 @@ int Start(int argc, char** argv) {
 
   v8_platform.Initialize(v8_thread_pool_size);
   V8::Initialize();
+  v8_initialized = true;
 
   int exit_code = 1;
   {
@@ -4908,6 +4910,7 @@ int Start(int argc, char** argv) {
     StartNodeInstance(&instance_data);
     exit_code = instance_data.exit_code();
   }
+  v8_initialized = false;
   V8::Dispose();
 
   v8_platform.Dispose();

src/node_internals.h

@@ -43,6 +43,9 @@ extern std::string openssl_config;
 // that is used by lib/module.js
 extern bool config_preserve_symlinks;
 
+// Tells whether it is safe to call v8::Isolate::GetCurrent().
+extern bool v8_initialized;
+
 // Set in node.cc by ParseArgs when --expose-internals or --expose_internals is
 // used.
 // Used in node_config.cc to set a constant on process.binding('config')

src/util-inl.h

@@ -344,7 +344,15 @@ T* UncheckedRealloc(T* pointer, size_t n) {
     return nullptr;
   }
 
-  return static_cast<T*>(realloc(pointer, full_size));
+  void* allocated = realloc(pointer, full_size);
+
+  if (UNLIKELY(allocated == nullptr)) {
+    // Tell V8 that memory is low and retry.
+    LowMemoryNotification();
+    allocated = realloc(pointer, full_size);
+  }
+
+  return static_cast<T*>(allocated);
 }
 
 // As per spec realloc behaves like malloc if passed nullptr.

src/util.cc

@@ -77,4 +77,13 @@ BufferValue::BufferValue(Isolate* isolate, Local<Value> value) {
   }
 }
 
+void LowMemoryNotification() {
+  if (v8_initialized) {
+    auto isolate = v8::Isolate::GetCurrent();
+    if (isolate != nullptr) {
+      isolate->LowMemoryNotification();
+    }
+  }
+}
+
 }  // namespace node

src/util.h

@@ -53,6 +53,11 @@ inline char* Calloc(size_t n) { return Calloc<char>(n); }
 inline char* UncheckedMalloc(size_t n) { return UncheckedMalloc<char>(n); }
 inline char* UncheckedCalloc(size_t n) { return UncheckedCalloc<char>(n); }
 
+// Used by the allocation functions when allocation fails.
+// Thin wrapper around v8::Isolate::LowMemoryNotification() that checks
+// whether V8 is initialized.
+void LowMemoryNotification();
+
 #ifdef __GNUC__
 #define NO_RETURN __attribute__((noreturn))
 #else