Safepointing in GC

runtime/vm/thread.h

 // Copyright (c) 2015, 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_THREAD_H_
 #define VM_THREAD_H_
 
 #include "vm/globals.h"
 #include "vm/os_thread.h"
 #include "vm/store_buffer.h"
@@ skipping 20 matching lines @@
   V(RawBool*, bool_false_, Object::bool_false().raw(), NULL)                   \
 
 #define CACHED_ADDRESSES_LIST(V)                                               \
   V(uword, update_store_buffer_entry_point_,                                   \
     StubCode::UpdateStoreBuffer_entry()->EntryPoint(), 0)
 
 #define CACHED_CONSTANTS_LIST(V)                                               \
   CACHED_VM_OBJECTS_LIST(V)                                                    \
   CACHED_ADDRESSES_LIST(V)
 
+// TODO(koda): Merge thread.h and thread_registry.h.
+typedef int64_t SafepointId;
+static const SafepointId kNoSafepointId = -1;
 
 // A VM thread; may be executing Dart code or performing helper tasks like
 // garbage collection or compilation. The Thread structure associated with
 // a thread is allocated by EnsureInit before entering an isolate, and destroyed
 // automatically when the underlying OS thread exits. NOTE: On Windows, CleanUp
 // must currently be called manually (issue 23474).
 class Thread {
  public:
   // The currently executing thread, or NULL if not yet initialized.
   static Thread* Current() {
     return reinterpret_cast<Thread*>(OSThread::GetThreadLocal(thread_key_));
   }
 
   // Initializes the current thread as a VM thread, if not already done.
   static void EnsureInit();
 
   // Makes the current thread enter 'isolate'.
   static void EnterIsolate(Isolate* isolate);
   // Makes the current thread exit its isolate.
   static void ExitIsolate();
 
   // A VM thread other than the main mutator thread can enter an isolate as a
   // "helper" to gain limited concurrent access to the isolate. One example is
   // SweeperTask (which uses the class table, which is copy-on-write).
   // TODO(koda): Properly synchronize heap access to expand allowed operations.
-  static void EnterIsolateAsHelper(Isolate* isolate);
+  //
+  // If 'pass_safepoint' is set to the current rendezvous (returned by
+  // ThreadRegistry::SafepointThreads), the thread will be allowed free passage
+  // into the isolate while this rendezvous is in progress.
+  static void EnterIsolateAsHelper(
+      Isolate* isolate,
+      SafepointId pass_safepoint = kNoSafepointId);
   static void ExitIsolateAsHelper();
 
   // Called when the current thread transitions from mutator to collector.
   // Empties the store buffer block into the isolate.
   // TODO(koda): Always run GC in separate thread.
   static void PrepareForGC();
 
 #if defined(TARGET_OS_WINDOWS)
   // Clears the state of the current thread and frees the allocation.
   static void CleanUp();
@@ skipping 149 matching lines @@
     state_.timeline_block = block;
   }
 
  private:
   static ThreadLocalKey thread_key_;
 
   Isolate* isolate_;
   Heap* heap_;
   State state_;
   StoreBufferBlock* store_buffer_block_;
+  SafepointId pass_safepoint_;
 #define DECLARE_MEMBERS(type_name, member_name, expr, default_init_value)      \
   type_name member_name;
 CACHED_CONSTANTS_LIST(DECLARE_MEMBERS)
 #undef DECLARE_MEMBERS
 
   explicit Thread(bool init_vm_constants = true);
 
   void InitVMConstants();
 
   void ClearState() {
@@ skipping 16 matching lines @@
   friend class ApiZone;
   friend class Isolate;
   friend class StackZone;
   friend class ThreadRegistry;
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_