GRPC-C++源码分析（六）--ServerCompletionQueue续

  CompletionQueue(const grpc_completion_queue_attributes& attributes) {
    cq_ = g_core_codegen_interface->grpc_completion_queue_create(
        g_core_codegen_interface->grpc_completion_queue_factory_lookup(
            &attributes),
        &attributes, NULL);
    InitialAvalanching();  // reserve this for the future shutdown
  }

//core_codegen.h
 class CoreCodegen final : public CoreCodegenInterface {
 private:
  virtual const grpc_completion_queue_factory*
  grpc_completion_queue_factory_lookup(
      const grpc_completion_queue_attributes* attributes) override;
  virtual grpc_completion_queue* grpc_completion_queue_create(
      const grpc_completion_queue_factory* factory,
      const grpc_completion_queue_attributes* attributes,
      void* reserved) override;

//completion_queue.cc
grpc_completion_queue* grpc_completion_queue_create_internal(
    grpc_cq_completion_type completion_type, grpc_cq_polling_type polling_type,
    grpc_experimental_completion_queue_functor* shutdown_callback) {
  GPR_TIMER_SCOPE("grpc_completion_queue_create_internal", 0);

//最终返回的的那个cq
  grpc_completion_queue* cq;

  GRPC_API_TRACE(
      "grpc_completion_queue_create_internal(completion_type=%d, "
      "polling_type=%d)",
      2, (completion_type, polling_type));

//这两个vtable是cq的核心内容
  const cq_vtable* vtable = &g_cq_vtable[completion_type];
  const cq_poller_vtable* poller_vtable =
      &g_poller_vtable_by_poller_type[polling_type];

  grpc_core::ExecCtx exec_ctx;
  GRPC_STATS_INC_CQS_CREATED();

//cq的初始化也很魔性，除了本身的大小，还额外预留了vtable->data_size + poller_vtable->size()
  cq = static_cast<grpc_completion_queue*>(
      gpr_zalloc(sizeof(grpc_completion_queue) + vtable->data_size +
                 poller_vtable->size()));

  //赋值给了cq里的变量
  cq->vtable = vtable;
  cq->poller_vtable = poller_vtable;

  /* One for destroy(), one for pollset_shutdown */
  gpr_ref_init(&cq->owning_refs, 2);

  //vtable的初始化
  poller_vtable->init(POLLSET_FROM_CQ(cq), &cq->mu);
  vtable->init(DATA_FROM_CQ(cq), shutdown_callback);

  GRPC_CLOSURE_INIT(&cq->pollset_shutdown_done, on_pollset_shutdown_done, cq,
                    grpc_schedule_on_exec_ctx);
  return cq;
}