MMTk代码学习(整体结构)

必要的整体模块

对于一个完整的内存管理工具，主要涉及：

• 内存映射(Address)
• 内存组织结构(Resource,Page)
• 基于内存结构的策略：分配、回收(Alloc, Collect)
  
• 内存跟踪(Trace, Log)

对应到MMTk的具体模块

系统结构

• Plan
  
   
• CollectorContext, MutatorContext 上下文环境
  • 所有collector都继承于CollectorContext(包含有run()方法接口用于线程化) TLS(Thread Local storage)
    
     
  • 所有mutator都继承于MutatorContext
    
     
• Phase, ConcurrentPhase, ComplexPhase：将GC分成多个过程，整个GC由若干Phase组成

内存映射

• Address

内存组织结构

• PageResource
• FreeListPageResource
• MonotonePageResource

主要流程

初始化

1. enableAllocation: allow allocation (but not collection).
2. processOptions: the VM has parsed/prepared options for MMTk to react to.
   
3. enableCollection: the VM can support the spawning of MMTk collector contexts.
4. fullyBooted: control is jst about to be given to application code.

分配对象

org.jikesrvm.mm.mminterface.MemoryManager

  /**
   * Allocate a scalar object.
   *
   * @param size Size in bytes of the object, including any headers
   * that need space.
   * @param tib  Type of the object (pointer to TIB).
   * @param allocator Specify which allocation scheme/area JMTk should
   * allocate the memory from.
   * @param align the alignment requested; must be a power of 2.
   * @param offset the offset at which the alignment is desired.
   * @param site allocation site.
   * @return the initialized Object
   */
  @Inline
  public static Object allocateScalar(int size, TIB tib, int allocator, int align, int offset, int site) {
    Selected.Mutator mutator = Selected.Mutator.get();
    allocator = mutator.checkAllocator(org.jikesrvm.runtime.Memory.alignUp(size, MIN_ALIGNMENT), align, allocator);
    Address region = allocateSpace(mutator, size, align, offset, allocator, site);
    Object result = ObjectModel.initializeScalar(region, tib, size);
    mutator.postAlloc(ObjectReference.fromObject(result), ObjectReference.fromObject(tib), size, allocator);
    return result;
  }

1. checkAllocator: 选择一个合适的allocator
2. allocateSpace: mutator.alloc(allocSlow:可能调用GC)
3. 初始化对象数据
4. mutator.postAlloc

垃圾收集

Alloc时触发

allocSlow

主动调用

org.jikesrvm.mm.mminterface.MemoryManager

  /**
   * External call to force a garbage collection.
   */
  @Interruptible
  public static void gc() {
    Selected.Plan.handleUserCollectionRequest();
  }