Introducing NoRJSScope

Summary: NoRJSScope is a RAII class to temporarily disallow JS execution.

Reviewed By: neildhar

Differential Revision: D43834350

fbshipit-source-id: cf1b6e874212ea95fb1ede61ad9bcc0d10d7cdfc

include/hermes/VM/Runtime.h

@@ -1377,6 +1377,12 @@ class HERMES_EMPTY_BASES Runtime : public PointerBase,
   /// making it optional. If this is accessed when the optional value is cleared
   /// (the invalid state) we assert.
   llvh::Optional<const inst::Inst *> currentIP_{(const inst::Inst *)nullptr};
+
+  /// The number of alive/active NoRJSScopes. If nonzero, then no JS execution
+  /// is allowed
+  uint32_t noRJSLevel_{0};
+
+  friend class NoRJSScope;
 #endif
 
  public:
@@ -1738,6 +1744,7 @@ class NoAllocScope {
   NoAllocScope() = delete;
 };
 using NoHandleScope = NoAllocScope;
+using NoRJSScope = NoAllocScope;
 
 #else
 
@@ -1809,6 +1816,14 @@ class NoAllocScope : public BaseNoScope {
   using BaseNoScope::BaseNoScope;
   using BaseNoScope::operator=;
 };
+
+/// RAII class to temporarily disallow reentering JS execution.
+class NoRJSScope : public BaseNoScope {
+ public:
+  explicit NoRJSScope(Runtime &runtime) : BaseNoScope(&runtime.noRJSLevel_) {}
+  using BaseNoScope::BaseNoScope;
+  using BaseNoScope::operator=;
+};
 #endif
 
 //===----------------------------------------------------------------------===//

lib/VM/Interpreter.cpp

@@ -827,6 +827,9 @@ CallResult<HermesValue> Runtime::interpretFunctionImpl(
 }
 
 CallResult<HermesValue> Runtime::interpretFunction(CodeBlock *newCodeBlock) {
+  // Make sure we are not re-entering JS execution from a context that doesn't
+  // allow reentrancy
+  assert(this->noRJSLevel_ == 0 && "No JS execution allowed right now.");
   return interpretFunctionImpl(newCodeBlock);
 }