Separate mutex for megamorphic cache tables lookup in the background compiler.

runtime/vm/isolate.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 264 matching lines @@
   void set_spawn_state(IsolateSpawnState* value) { spawn_state_ = value; }
 
   Mutex* mutex() const { return mutex_; }
   Mutex* symbols_mutex() const { return symbols_mutex_; }
   Mutex* type_canonicalization_mutex() const {
     return type_canonicalization_mutex_;
   }
   Mutex* constant_canonicalization_mutex() const {
     return constant_canonicalization_mutex_;
   }
+  Mutex* lookup_mutex() const { return lookup_mutex_; }
 
   Debugger* debugger() const {
     if (!FLAG_support_debugger) {
       return NULL;
     }
     ASSERT(debugger_ != NULL);
     return debugger_;
   }
 
   void set_single_step(bool value) { single_step_ = value; }
@@ skipping 415 matching lines @@
   Debugger* debugger_;
   bool resume_request_;
   int64_t last_resume_timestamp_;
   bool has_compiled_code_;  // Can check that no compilation occured.
   Random random_;
   Simulator* simulator_;
   Mutex* mutex_;  // Protects compiler stats.
   Mutex* symbols_mutex_;  // Protects concurrent access to the symbol table.
   Mutex* type_canonicalization_mutex_;  // Protects type canonicalization.
   Mutex* constant_canonicalization_mutex_;  // Protects const canonicalization.
+  Mutex* lookup_mutex_;  // Protects megamorphic table lookup.

[siva, 2016/07/01 17:39:29]

can we call it megamorphic_lookup_mutex_;
so that it is more clear and people don't use it for other lookups.

[Florian Schneider, 2016/07/01 19:31:58]

Done.

   MessageHandler* message_handler_;
   IsolateSpawnState* spawn_state_;
   bool is_runnable_;
   Dart_GcPrologueCallback gc_prologue_callback_;
   Dart_GcEpilogueCallback gc_epilogue_callback_;
   intptr_t defer_finalization_count_;
   DeoptContext* deopt_context_;
 
   bool is_service_isolate_;
 
@@ skipping 243 matching lines @@
   intptr_t* spawn_count_;
 
   Dart_IsolateFlags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_