// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_DISCARDABLE_MEMORY_SERVICE_DISCARDABLE_SHARED_MEMORY_MANAGER_H_
#define COMPONENTS_DISCARDABLE_MEMORY_SERVICE_DISCARDABLE_SHARED_MEMORY_MANAGER_H_

#include <stddef.h>
#include <stdint.h>

#include <memory>
#include <unordered_map>
#include <vector>

#include "base/format_macros.h"
#include "base/functional/callback.h"
#include "base/memory/discardable_memory_allocator.h"
#include "base/memory/discardable_shared_memory.h"
#include "base/memory/memory_pressure_listener.h"
#include "base/memory/ref_counted.h"
#include "base/memory/unsafe_shared_memory_region.h"
#include "base/memory/weak_ptr.h"
#include "base/process/process_handle.h"
#include "base/synchronization/lock.h"
#include "base/task/current_thread.h"
#include "base/task/sequenced_task_runner.h"
#include "base/task/single_thread_task_runner.h"
#include "base/thread_annotations.h"
#include "base/trace_event/memory_dump_provider.h"
#include "components/discardable_memory/common/discardable_memory_export.h"
#include "components/discardable_memory/public/mojom/discardable_shared_memory_manager.mojom.h"
#include "mojo/public/cpp/bindings/pending_receiver.h"

namespace base {
class WaitableEvent;
}

namespace discardable_memory {

namespace {
class TestDiscardableSharedMemoryManager;
}  // namespace

// Implementation of DiscardableMemoryAllocator that allocates and manages
// discardable memory segments for the process which hosts this class, and
// for remote processes which request discardable memory from this class via
// IPC.
// This class is thread-safe and instances can safely be used on any thread.
class DISCARDABLE_MEMORY_EXPORT DiscardableSharedMemoryManager
    : public base::DiscardableMemoryAllocator,
      public base::trace_event::MemoryDumpProvider,
      public base::CurrentThread::DestructionObserver {
 public:
  DiscardableSharedMemoryManager();

  DiscardableSharedMemoryManager(const DiscardableSharedMemoryManager&) =
      delete;
  DiscardableSharedMemoryManager& operator=(
      const DiscardableSharedMemoryManager&) = delete;

  ~DiscardableSharedMemoryManager() override;

  // Returns the global instance of DiscardableSharedMemoryManager, usable from
  // any thread. May return null if no DiscardableSharedMemoryManager has been
  // created in the current process.
  static DiscardableSharedMemoryManager* Get();

  // Bind the manager to a mojo interface receiver.
  void Bind(
      mojo::PendingReceiver<mojom::DiscardableSharedMemoryManager> receiver);

  // Overridden from base::DiscardableMemoryAllocator:
  std::unique_ptr<base::DiscardableMemory> AllocateLockedDiscardableMemory(
      size_t size) override;

  // Overridden from base::trace_event::MemoryDumpProvider:
  bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
                    base::trace_event::ProcessMemoryDump* pmd) override;

  // This allocates a discardable memory segment for |process_handle|.
  // A valid shared memory region is returned on success.
  void AllocateLockedDiscardableSharedMemoryForClient(
      int client_id,
      size_t size,
      int32_t id,
      base::UnsafeSharedMemoryRegion* shared_memory_region);

  // Call this to notify the manager that client process associated with
  // |client_id| has deleted discardable memory segment with |id|.
  void ClientDeletedDiscardableSharedMemory(int32_t id, int client_id);

  // Call this to notify the manager that client associated with |client_id|
  // has been removed. The manager will use this to release memory segments
  // allocated for client to the OS.
  void ClientRemoved(int client_id);

  // The maximum number of bytes of memory that may be allocated. This will
  // cause memory usage to be reduced if currently above |limit|.
  void SetMemoryLimit(size_t limit);

  // Reduce memory usage if above current memory limit.
  void EnforceMemoryPolicy();

  // Returns bytes of allocated discardable memory.
  size_t GetBytesAllocated() const override;

  void ReleaseFreeMemory() override {
    // Do nothing since we already subscribe to memory pressure notifications.
  }

 private:
  friend TestDiscardableSharedMemoryManager;

  class MemorySegment : public base::RefCountedThreadSafe<MemorySegment> {
   public:
    MemorySegment(std::unique_ptr<base::DiscardableSharedMemory> memory);

    MemorySegment(const MemorySegment&) = delete;
    MemorySegment& operator=(const MemorySegment&) = delete;

    base::DiscardableSharedMemory* memory() const { return memory_.get(); }

   private:
    friend class base::RefCountedThreadSafe<MemorySegment>;

    ~MemorySegment();

    std::unique_ptr<base::DiscardableSharedMemory> memory_;
  };

  static bool CompareMemoryUsageTime(const scoped_refptr<MemorySegment>& a,
                                     const scoped_refptr<MemorySegment>& b) {
    // In this system, LRU memory segment is evicted first.
    return a->memory()->last_known_usage() > b->memory()->last_known_usage();
  }

  // base::CurrentThread::DestructionObserver implementation:
  void WillDestroyCurrentMessageLoop() override;

  void AllocateLockedDiscardableSharedMemory(
      int client_id,
      size_t size,
      int32_t id,
      base::UnsafeSharedMemoryRegion* shared_memory_region);
  void DeletedDiscardableSharedMemory(int32_t id, int client_id);
  // Virtual for tests.
  virtual void OnMemoryPressure(
      base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
  void ReduceMemoryUsageUntilWithinMemoryLimit()
      EXCLUSIVE_LOCKS_REQUIRED(lock_);
  void ReduceMemoryUsageUntilWithinLimit(size_t limit)
      EXCLUSIVE_LOCKS_REQUIRED(lock_);
  void ReleaseMemory(base::DiscardableSharedMemory* memory)
      EXCLUSIVE_LOCKS_REQUIRED(lock_);
  void BytesAllocatedChanged(size_t new_bytes_allocated) const;

  // Virtual for tests.
  virtual base::Time Now() const;
  virtual void ScheduleEnforceMemoryPolicy() EXCLUSIVE_LOCKS_REQUIRED(lock_);

  // Invalidate weak pointers for the mojo thread.
  void InvalidateMojoThreadWeakPtrs(base::WaitableEvent* event);

  // Create `memory_pressure_listener_` on a worker thread to receive memory
  // pressure notifications there.
  void CreateMemoryPressureListenerOnWorkerThread();

  int32_t next_client_id_;

  mutable base::Lock lock_;
  using MemorySegmentMap =
      std::unordered_map<int32_t, scoped_refptr<MemorySegment>>;
  using ClientMap = std::unordered_map<int, MemorySegmentMap>;
  ClientMap clients_ GUARDED_BY(lock_);
  // Note: The elements in |segments_| are arranged in such a way that they form
  // a heap. The LRU memory segment always first.
  using MemorySegmentVector = std::vector<scoped_refptr<MemorySegment>>;
  MemorySegmentVector segments_ GUARDED_BY(lock_);
  size_t default_memory_limit_ GUARDED_BY(lock_);
  size_t memory_limit_ GUARDED_BY(lock_);
  size_t bytes_allocated_ GUARDED_BY(lock_);
  std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_
      GUARDED_BY(lock_);
  scoped_refptr<base::SingleThreadTaskRunner> enforce_memory_policy_task_runner_
      GUARDED_BY(lock_);
  base::RepeatingClosure enforce_memory_policy_callback_ GUARDED_BY(lock_);
  bool enforce_memory_policy_pending_ GUARDED_BY(lock_);

  // The message loop for running mojom::DiscardableSharedMemoryManager
  // implementations.
  // TODO(altimin,gab): Allow weak pointers to be deleted on other threads
  // when the thread is gone and remove this.
  // A prerequisite for this is allowing objects to be bound to the lifetime
  // of a sequence directly.
  base::CurrentThread mojo_thread_message_loop_;
  scoped_refptr<base::SingleThreadTaskRunner> mojo_thread_task_runner_;

  // A task runner to create `memory_pressure_listener_` on worker threads so
  // that `OnMemoryPressure` notification happens on the worker thread too.
  scoped_refptr<base::SequencedTaskRunner> memory_pressure_task_runner_;

  base::WeakPtrFactory<DiscardableSharedMemoryManager> weak_ptr_factory_{this};

  // WeakPtrFractory for generating weak pointers used in the mojo thread.
  base::WeakPtrFactory<DiscardableSharedMemoryManager>
      mojo_thread_weak_ptr_factory_{this};
};

}  // namespace discardable_memory

#endif  // COMPONENTS_DISCARDABLE_MEMORY_SERVICE_DISCARDABLE_SHARED_MEMORY_MANAGER_H_