ut0todo_counter.h

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#pragma once
 
#include <cstddef>
#include "os0event.h"
#include "ut0dbg.h"
 
namespace ut {
/** A counter which tracks number of things left to do, which can be
incremented or decremented, and lets one await the value drop to zero.
Enforcing a total order on calls to increment(), decrement() and value() is
a responsibility of a user of this class.
With above assumption the await_zero() can be called safely at any moment,
as increment() and decrement() take care of resetting and setting the awaited
event object properly. */
class Todo_counter {
 public:
  /** Initializes the counter to 0. */
  Todo_counter() { os_event_set(m_is_zero); }
 
  /** Increments the value of the counter */
  void increment() {
    if (!m_todos++) {
      os_event_reset(m_is_zero);
    }
  }
 
  /** Decrements the value of the counter */
  void decrement() {
    ut_a(0 < m_todos);
    if (!--m_todos) {
      os_event_set(m_is_zero);
    }
  }
 
  /** Returns when the value is zero */
  void await_zero() { os_event_wait(m_is_zero); }
 
  /** Returns current value of the counter */
  size_t value() { return m_todos; }
 
 private:
  size_t m_todos{0};
  Os_event_t m_is_zero{};
};
}  // namespace ut