shared_thread_merger.h

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// Copyright 2013 The Flutter 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 FLUTTER_FML_SHARED_THREAD_MERGER_H_
#define FLUTTER_FML_SHARED_THREAD_MERGER_H_
 
#include <condition_variable>
#include <mutex>
 
#include "flutter/fml/macros.h"
#include "flutter/fml/memory/ref_counted.h"
#include "flutter/fml/message_loop_task_queues.h"
 
namespace fml {
 
class RasterThreadMerger;
 
typedef void* RasterThreadMergerId;
 
/// Instance of this class is shared between multiple |RasterThreadMerger|
/// instances, Most of the callings from |RasterThreadMerger| will be redirected
/// to this class with one more caller parameter.
class SharedThreadMerger
    : public fml::RefCountedThreadSafe<SharedThreadMerger> {
 public:
  SharedThreadMerger(TaskQueueId owner, TaskQueueId subsumed);
 
  // It's called by |RasterThreadMerger::MergeWithLease|.
  // See the doc of |RasterThreadMerger::MergeWithLease|.
  bool MergeWithLease(RasterThreadMergerId caller, size_t lease_term);
 
  // It's called by |RasterThreadMerger::UnMergeNowIfLastOne|.
  // See the doc of |RasterThreadMerger::UnMergeNowIfLastOne|.
  bool UnMergeNowIfLastOne(RasterThreadMergerId caller);
 
  // It's called by |RasterThreadMerger::ExtendLeaseTo|.
  // See the doc of |RasterThreadMerger::ExtendLeaseTo|.
  void ExtendLeaseTo(RasterThreadMergerId caller, size_t lease_term);
 
  // It's called by |RasterThreadMerger::IsMergedUnSafe|.
  // See the doc of |RasterThreadMerger::IsMergedUnSafe|.
  bool IsMergedUnSafe() const;
 
  // It's called by |RasterThreadMerger::IsEnabledUnSafe|.
  // See the doc of |RasterThreadMerger::IsEnabledUnSafe|.
  bool IsEnabledUnSafe() const;
 
  // It's called by |RasterThreadMerger::Enable| or
  // |RasterThreadMerger::Disable|.
  void SetEnabledUnSafe(bool enabled);
 
  // It's called by |RasterThreadMerger::DecrementLease|.
  // See the doc of |RasterThreadMerger::DecrementLease|.
  bool DecrementLease(RasterThreadMergerId caller);
 
 private:
  fml::TaskQueueId owner_;
  fml::TaskQueueId subsumed_;
  fml::MessageLoopTaskQueues* task_queues_;
  std::mutex mutex_;
  bool enabled_ = false;
 
  /// The |MergeWithLease| or |ExtendLeaseTo| method will record the caller
  /// into this lease_term_by_caller_ map, |UnMergeNowIfLastOne|
  /// method will remove the caller from this lease_term_by_caller_.
  std::map<RasterThreadMergerId, std::atomic_size_t> lease_term_by_caller_;
 
  bool IsAllLeaseTermsZeroUnSafe() const;
 
  bool UnMergeNowUnSafe();
 
  FML_DISALLOW_COPY_AND_ASSIGN(SharedThreadMerger);
};
 
}  // namespace fml
 
#endif  // FLUTTER_FML_SHARED_THREAD_MERGER_H_