text: // Copyright (c) 2016 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef COMPONENTS_VIZ_COMMON_GPU_CONTEXT_CACHE_CONTROLLER_H_
  #define COMPONENTS_VIZ_COMMON_GPU_CONTEXT_CACHE_CONTROLLER_H_
  
  #include <cstdint>
  #include <memory>
  
  #include "base/macros.h"
  #include "base/memory/ref_counted.h"
  #include "base/memory/weak_ptr.h"
  #include "base/single_thread_task_runner.h"
  #include "components/viz/common/viz_common_export.h"
  
  class GrContext;
  
  namespace base {
  class Lock;
  }
  
  namespace gpu {
  class ContextSupport;
  }
  
  namespace viz {
  
  // ContextCacheController manages clearing cached data on ContextProvider when
  // appropriate. Currently, cache clearing is triggered when the Context
  // provider transitions from Visible to Not Visible, or from Busy to Idle. As a
  // ContextProvider may have multiple clients, ContextCacheController tracks
  // visibility and idle status across all clients and only cleans up when
  // appropriate.
  class VIZ_COMMON_EXPORT ContextCacheController {
   public:
    class VIZ_COMMON_EXPORT ScopedToken {
     public:
      ~ScopedToken();
  
     private:
      friend class ContextCacheController;
      ScopedToken();
      void Release();
  
      bool released_ = false;
    };
    using ScopedVisibility = ScopedToken;
    using ScopedBusy = ScopedToken;
  
    ContextCacheController(
        gpu::ContextSupport* context_support,
        scoped_refptr<base::SingleThreadTaskRunner> task_runner);
    virtual ~ContextCacheController();
  
    void SetGrContext(GrContext* gr_context);
    void SetLock(base::Lock* lock);
  
    // Clients of the owning ContextProvider should call this function when they
    // become visible. The returned ScopedVisibility pointer must be passed back
    // to ClientBecameNotVisible or it will DCHECK in its destructor.
    virtual std::unique_ptr<ScopedVisibility> ClientBecameVisible();
  
    // When a client becomes not visible (either due to a visibility change or
    // because it is being deleted), it must pass back any ScopedVisibility
    // pointers it owns via this function.
    virtual void ClientBecameNotVisible(
        std::unique_ptr<ScopedVisibility> scoped_visibility);
  
    // When a client becomes not visible because it is being deleted, hold on to
    // the visibility token so that we don't aggressively free resources that are
    // still going to be used. Instead, release the token when this is deleted.
    virtual void ClientBecameNotVisibleDuringShutdown(
        std::unique_ptr<ScopedVisibility> scoped_visibility);
  
    // Clients of the owning ContextProvider may call this function when they
    // become busy. The returned ScopedBusy pointer must be passed back
    // to ClientBecameNotBusy or it will DCHECK in its destructor.
    std::unique_ptr<ScopedBusy> ClientBecameBusy();
  
    // When a client becomes not busy, it must pass back any ScopedBusy
    // pointers it owns via this function.
    void ClientBecameNotBusy(std::unique_ptr<ScopedBusy> scoped_busy);
  
   private:
    void OnIdle(uint32_t idle_generation);
    void PostIdleCallback(uint32_t current_idle_generation) const;
    void InvalidatePendingIdleCallbacks();
  
    gpu::ContextSupport* context_support_;
    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
    GrContext* gr_context_ = nullptr;
  
    std::unique_ptr<ScopedVisibility> held_visibility_;
  
    // If set, |context_lock_| must be held before accessing any member within
    // the idle callback. Exceptions to this are |current_idle_generation_|,
    // which has its own lock, and weak_ptr_ and task_runner_, which may be
    // accessed from multiple threads without locking.
    base::Lock* context_lock_ = nullptr;
  
    uint32_t num_clients_visible_ = 0;
    uint32_t num_clients_busy_ = 0;
    bool callback_pending_ = false;
  
    // |current_idle_generation_lock_| must be held when accessing
    // |current_idle_generation_|. |current_idle_generation_lock_| must never be
    // held while acquiring |context_lock_|.
    base::Lock current_idle_generation_lock_;
    uint32_t current_idle_generation_ = 0;
  
    base::WeakPtr<ContextCacheController> weak_ptr_;
    base::WeakPtrFactory<ContextCacheController> weak_factory_{this};
  };
  
  }  // namespace viz
  
  #endif  // COMPONENTS_VIZ_COMMON_GPU_CONTEXT_CACHE_CONTROLLER_H_
  