Fix a race condition in simulator that happens when flushing icache.

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 172 matching lines @@
 
 AssemblerBase::~AssemblerBase() {
   if (own_buffer_) DeleteArray(buffer_);
 }
 
 
 void AssemblerBase::FlushICache(Isolate* isolate, void* start, size_t size) {
   if (size == 0) return;
 
 #if defined(USE_SIMULATOR)
+  base::LockGuard<base::Mutex> lock_guard(isolate->simulator_i_cache_mutex());
   Simulator::FlushICache(isolate->simulator_i_cache(), start, size);
 #else
   CpuFeatures::FlushICache(start, size);
 #endif  // USE_SIMULATOR
 }
 
 
 void AssemblerBase::Print() {
   OFStream os(stdout);
   v8::internal::Disassembler::Decode(isolate(), &os, buffer_, pc_, nullptr);
@@ skipping 1753 matching lines @@
 
 
 void Assembler::DataAlign(int m) {
   DCHECK(m >= 2 && base::bits::IsPowerOfTwo32(m));
   while ((pc_offset() & (m - 1)) != 0) {
     db(0);
   }
 }
 }  // namespace internal
 }  // namespace v8