- Use the simulator to do atomic operations that could also

runtime/vm/simulator_arm64.h

 // Copyright (c) 2014, 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.
 
 // Declares a Simulator for ARM64 instructions if we are not generating a native
 // ARM64 binary. This Simulator allows us to run and debug ARM64 code generation
 // on regular desktop machines.
 // Dart calls into generated code by "calling" the InvokeDartCode stub,
 // which will start execution in the Simulator or forwards to the real entry
 // on a ARM64 HW platform.
 
 #ifndef VM_SIMULATOR_ARM64_H_
 #define VM_SIMULATOR_ARM64_H_
 
 #ifndef VM_SIMULATOR_H_
 #error Do not include simulator_arm64.h directly; use simulator.h.
 #endif
 
 #include "vm/constants_arm64.h"
-#include "vm/object.h"
 
 namespace dart {
 
 class Isolate;
+class Mutex;
+class RawObject;
 class SimulatorSetjmpBuffer;
 
 typedef struct {
   union {
     int64_t i64[2];
     int32_t i32[4];
   } bits;
 } simd_value_t;
 
 class Simulator {
@@ skipping 35 matching lines @@
   // Accessor to the internal simulator stack top.
   uword StackTop() const;
 
   // The isolate's top_exit_frame_info refers to a Dart frame in the simulator
   // stack. The simulator's top_exit_frame_info refers to a C++ frame in the
   // native stack.
   uword top_exit_frame_info() const { return top_exit_frame_info_; }
   void set_top_exit_frame_info(uword value) { top_exit_frame_info_ = value; }
 
   // Call on program start.
-  static void InitOnce() {}
+  static void InitOnce();
 
   // Dart generally calls into generated code with 5 parameters. This is a
   // convenience function, which sets up the simulator state and grabs the
   // result on return. The return value is R0. The parameters are placed in
   // R0-3.
   int64_t Call(int64_t entry,
                int64_t parameter0,
                int64_t parameter1,
                int64_t parameter2,
                int64_t parameter3,
                bool fp_return = false,
                bool fp_args = false);
 
+  // Implementation of atomic compare and exchange in the same synchronization
+  // domain as other synchronization primitive instructions (e.g. ldrex, strex).
+  static uword CompareExchange(uword* address,
+                               uword compare_value,
+                               uword new_value);
+
   // Runtime and native call support.
   enum CallKind {
     kRuntimeCall,
     kLeafRuntimeCall,
     kLeafFloatRuntimeCall,
     kBootstrapNativeCall,
     kNativeCall
   };
   static uword RedirectExternalReference(uword function,
                                          CallKind call_kind,
@@ skipping 62 matching lines @@
   inline int16_t ReadH(uword addr, Instr* instr);
   inline void WriteH(uword addr, uint16_t value, Instr* instr);
 
   inline uint32_t ReadWU(uword addr, Instr* instr);
   inline int32_t ReadW(uword addr, Instr* instr);
   inline void WriteW(uword addr, uint32_t value, Instr* instr);
 
   inline intptr_t ReadX(uword addr, Instr* instr);
   inline void WriteX(uword addr, intptr_t value, Instr* instr);
 
+  // In Dart, there is at most one thread per isolate.
+  // We keep track of 16 exclusive access address tags across all isolates.
+  // Since we cannot simulate a native context switch, which clears
+  // the exclusive access state of the local monitor (using the CLREX
+  // instruction), we associate the isolate requesting exclusive access to the
+  // address tag. Multiple isolates requesting exclusive access (using the LDREX
+  // instruction) to the same address will result in multiple address tags being
+  // created for the same address, one per isolate.
+  // At any given time, each isolate is associated to at most one address tag.
+  static Mutex* exclusive_access_lock_;
+  static const int kNumAddressTags = 16;
+  static struct AddressTag {
+    Isolate* isolate;
+    uword addr;
+  } exclusive_access_state_[kNumAddressTags];
+  static int next_address_tag_;
+
+  // Synchronization primitives support.
+  void ClearExclusive();
+  intptr_t ReadExclusiveW(uword addr, Instr* instr);
+  intptr_t WriteExclusiveW(uword addr, intptr_t value, Instr* instr);
+
+  // Set access to given address to 'exclusive state' for current isolate.
+  static void SetExclusiveAccess(uword addr);
+
+  // Returns true if the current isolate has exclusive access to given address,
+  // returns false otherwise. In either case, set access to given address to
+  // 'open state' for all isolates.
+  // If given addr is NULL, set access to 'open state' for current
+  // isolate (CLREX).
+  static bool HasExclusiveAccessAndOpen(uword addr);
+
   // Helper functions to set the conditional flags in the architecture state.
   void SetNZFlagsW(int32_t val);
   bool CarryFromW(int32_t left, int32_t right, int32_t carry);
   bool OverflowFromW(int32_t left, int32_t right, int32_t carry);
 
   void SetNZFlagsX(int64_t val);
   bool CarryFromX(int64_t alu_out, int64_t left, int64_t right, bool addition);
   bool OverflowFromX(
       int64_t alu_out, int64_t left, int64_t right, bool addition);
 
@@ skipping 35 matching lines @@
   }
 
   friend class SimulatorDebugger;
   friend class SimulatorSetjmpBuffer;
   DISALLOW_COPY_AND_ASSIGN(Simulator);
 };
 
 }  // namespace dart
 
 #endif  // VM_SIMULATOR_ARM64_H_