[simulator] Make reference redirection thread-safe.

src/mips/simulator-mips.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 // Declares a Simulator for MIPS instructions if we are not generating a native
 // MIPS binary. This Simulator allows us to run and debug MIPS code generation
 // on regular desktop machines.
 // V8 calls into generated code by "calling" the CALL_GENERATED_CODE macro,
 // which will start execution in the Simulator or forwards to the real entry
@@ skipping 445 matching lines @@
     none,
     kIntegerOverflow,
     kIntegerUnderflow,
     kDivideByZero,
     kNumExceptions
   };
 
   // Exceptions.
   void SignalException(Exception e);
 
-  // Runtime call support.
+  // Runtime call support. Uses the isolate in a thread-safe way.
   static void* RedirectExternalReference(Isolate* isolate,
                                          void* external_function,
                                          ExternalReference::Type type);
 
   // Handle arguments and return value for runtime FP functions.
   void GetFpArgs(double* x, double* y, int32_t* z);
   void SetFpResult(const double& result);
 
   void CallInternal(byte* entry);
 
@@ skipping 73 matching lines @@
   static inline void UnregisterCTryCatch(Isolate* isolate) {
     Simulator::current(isolate)->PopAddress();
   }
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // !defined(USE_SIMULATOR)
 #endif  // V8_MIPS_SIMULATOR_MIPS_H_