art heap创建流程

通过前面的博客我们知道在art 创建的时候，会创建出heap实例，也就是管理art 的堆的对象。

art/runtime/runtime.cc

932  bool Runtime::Init(RuntimeArgumentMap&& runtime_options_in) {
...
1015    heap_ = new gc::Heap(runtime_options.GetOrDefault(Opt::MemoryInitialSize),
1016                         runtime_options.GetOrDefault(Opt::HeapGrowthLimit),
1017                         runtime_options.GetOrDefault(Opt::HeapMinFree),
1018                         runtime_options.GetOrDefault(Opt::HeapMaxFree),
1019                         runtime_options.GetOrDefault(Opt::HeapTargetUtilization),
1020                         runtime_options.GetOrDefault(Opt::ForegroundHeapGrowthMultiplier),
1021                         runtime_options.GetOrDefault(Opt::MemoryMaximumSize),
1022                         runtime_options.GetOrDefault(Opt::NonMovingSpaceCapacity),
1023                         runtime_options.GetOrDefault(Opt::Image),
1024                         runtime_options.GetOrDefault(Opt::ImageInstructionSet),
1025                         xgc_option.collector_type_,
1026                         runtime_options.GetOrDefault(Opt::BackgroundGc),
1027                         runtime_options.GetOrDefault(Opt::LargeObjectSpace),
1028                         runtime_options.GetOrDefault(Opt::LargeObjectThreshold),
1029                         runtime_options.GetOrDefault(Opt::ParallelGCThreads),
1030                         runtime_options.GetOrDefault(Opt::ConcGCThreads),
1031                         runtime_options.Exists(Opt::LowMemoryMode),
1032                         runtime_options.GetOrDefault(Opt::LongPauseLogThreshold),
1033                         runtime_options.GetOrDefault(Opt::LongGCLogThreshold),
1034                         runtime_options.Exists(Opt::IgnoreMaxFootprint),
1035                         runtime_options.GetOrDefault(Opt::UseTLAB),
1036                         xgc_option.verify_pre_gc_heap_,
1037                         xgc_option.verify_pre_sweeping_heap_,
1038                         xgc_option.verify_post_gc_heap_,
1039                         xgc_option.verify_pre_gc_rosalloc_,
1040                         xgc_option.verify_pre_sweeping_rosalloc_,
1041                         xgc_option.verify_post_gc_rosalloc_,
1042                         xgc_option.gcstress_,
1043                         runtime_options.GetOrDefault(Opt::EnableHSpaceCompactForOOM),
1044                         runtime_options.GetOrDefault(Opt::HSpaceCompactForOOMMinIntervalsMs));
1045  
1046    if (!heap_->HasBootImageSpace() && !allow_dex_file_fallback_) {
1047      LOG(ERROR) << "Dex file fallback disabled, cannot continue without image.";
1048      return false;
1049    }
...
1310    return true;
1311  }

接下里我们分析一下heap 创建过程中做了什么，主要是把创建不同space 的代码列出来。

art/runtime/gc/heap.cc

128  Heap::Heap(size_t initial_size,
   ...
157             uint64_t min_interval_homogeneous_space_compaction_by_oom)
158      : non_moving_space_(nullptr),
...
250        gc_disabled_for_shutdown_(false) {
...
267    live_bitmap_.reset(new accounting::HeapBitmap(this)); //记录上一次gc后还存活的对象
268    mark_bitmap_.reset(new accounting::HeapBitmap(this)); //记录当前gc后还存活的对象
...
278   // Load image space(s).
279    if (!image_file_name.empty()) {  //image_file_name 这个参数是 /system/framework/arm64/boot.art
280      // For code reuse, handle this like a work queue.
281      std::vector<std::string> image_file_names;
282      image_file_names.push_back(image_file_name); //将image_file_name 放到集合中，这时只有一个元素
...
287      for (size_t index = 0; index < image_file_names.size(); ++index) { //开始只有一个元素，但是往下运行的时候又添加了几个
288        std::string& image_name = image_file_names[index];
289        std::string error_msg;
290        space::ImageSpace* boot_image_space = space::ImageSpace::CreateBootImage(  //打开art文件，映射到内存，同时加载对应的oat文件
291            image_name.c_str(),
292            image_instruction_set,
293            index > 0,
294            &error_msg);
295        if (boot_image_space != nullptr) {
296          AddSpace(boot_image_space); //加到space里面
...
305          if (index == 0) {   //是第一个元素的时候，判断是否还有要加载的art文件
306            // If this was the first space, check whether there are more images to load.
307            const OatFile* boot_oat_file = boot_image_space->GetOatFile();
308            if (boot_oat_file == nullptr) {
309              continue;
310            }
311  
312            const OatHeader& boot_oat_header = boot_oat_file->GetOatHeader();
313            const char* boot_classpath =
314                boot_oat_header.GetStoreValueByKey(OatHeader::kBootClassPathKey);
315            if (boot_classpath == nullptr) {
316              continue;
317            }
318            //将其他要加载的art文件放到image_file_names 集合中，所以这个集合的长度不是1了
319            space::ImageSpace::ExtractMultiImageLocations(image_file_name,
320                                                          boot_classpath,
321                                                          &image_file_names);
322          }
323        } else {
...
336      }
337    }
...
369    std::unique_ptr<MemMap> main_mem_map_1;
370    std::unique_ptr<MemMap> main_mem_map_2;
...
385   std::unique_ptr<MemMap> non_moving_space_mem_map;
...      //static const char* kZygoteSpaceName = "zygote space";
391      const char* space_name = is_zygote ? kZygoteSpaceName: kNonMovingSpaceName;
394      non_moving_space_mem_map.reset(  //映射的是zygote space
395          MemMap::MapAnonymous(space_name, requested_alloc_space_begin,
396                               non_moving_space_capacity, PROT_READ | PROT_WRITE, true, false,
397                               &error_str));
...         
           // static const char* kMemMapSpaceName[2] = {"main space", "m