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// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_TASK_SEQUENCE_MANAGER_ENQUEUE_ORDER_H_
#define BASE_TASK_SEQUENCE_MANAGER_ENQUEUE_ORDER_H_
#include <stdint.h>
#include <limits>
namespace base {
namespace sequence_manager {
namespace internal {
class EnqueueOrderGenerator;
}
// 64-bit number which is used to order tasks.
// SequenceManager assumes this number will never overflow.
class EnqueueOrder {
public:
EnqueueOrder() : value_(kNone) {}
~EnqueueOrder() = default;
static EnqueueOrder none() { return EnqueueOrder(kNone); }
static EnqueueOrder blocking_fence() { return EnqueueOrder(kBlockingFence); }
// Returns an EnqueueOrder that compares greater than any other EnqueueOrder.
static EnqueueOrder max() {
return EnqueueOrder(std::numeric_limits<uint64_t>::max());
}
// It's okay to use EnqueueOrder in boolean expressions keeping in mind
// that some non-zero values have a special meaning.
operator uint64_t() const { return value_; }
static EnqueueOrder FromIntForTesting(uint64_t value) {
return EnqueueOrder(value);
}
private:
// EnqueueOrderGenerator is the only class allowed to create an EnqueueOrder
// with a non-default constructor.
friend class internal::EnqueueOrderGenerator;
explicit EnqueueOrder(uint64_t value) : value_(value) {}
enum SpecialValues : uint64_t {
kNone = 0,
kBlockingFence = 1,
kFirst = 2,
};
uint64_t value_;
};
} // namespace sequence_manager
} // namespace base
#endif // BASE_TASK_SEQUENCE_MANAGER_ENQUEUE_ORDER_H_
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