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一個共用/獨占鎖定，又稱為讀寫鎖定。

en.wikipedia.org/wiki/Readers%E2%80%93writer_lock

方法
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N
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Y
包含的模組

類別公用方法

new()

來源： 顯示 | 在 GitHub 上

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 49
def initialize
  super()

  @cv = new_cond

  @sharing = Hash.new(0)
  @waiting = {}
  @sleeping = {}
  @exclusive_thread = nil
  @exclusive_depth = 0
end

執行個體公用方法

exclusive(purpose: nil, compatible: [], after_compatible: [], no_wait: false)

在取得獨占鎖定的同時，執行所提供的區塊。如果設定 no_wait，而且鎖定無法立刻使用，會回傳 nil 而不進行讓與。否則，回傳區塊的結果。

請參閱 start_exclusive 以取得其他選項。

來源： 顯示 | 在 GitHub 上

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 147
def exclusive(purpose: nil, compatible: [], after_compatible: [], no_wait: false)
  if start_exclusive(purpose: purpose, compatible: compatible, no_wait: no_wait)
    begin
      yield
    ensure
      stop_exclusive(compatible: after_compatible)
    end
  end
end

sharing()

在取得共用鎖定的同時，執行所提供的區塊。

來源： 顯示 | 在 GitHub 上

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 158
def sharing
  start_sharing
  begin
    yield
  ensure
    stop_sharing
  end
end

start_exclusive(purpose: nil, compatible: [], no_wait: false)

如果設定 no_wait，而且鎖定無法立刻使用，回傳 false。否則，在取得鎖定後回傳 true。

purpose 和 compatible 共同作用；當這個執行緒在等待獨占鎖定時，它會將共用 (若有) 讓與給其他嘗試，而這些嘗試的 purpose 出現在此嘗試的 compatible 清單中。這允許「鬆散」升級，這種升級並不那麼嚴格，可以防止某些類型的死結。

對於許多資源來說，鬆散升級已經足夠：如果一個執行緒正在等待鎖定，它不會執行任何其他程式碼。只要 purpose 相符，就可以只讓與給不互相干擾的執行緒。

來源： 顯示 | 在 GitHub 上

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 75
def start_exclusive(purpose: nil, compatible: [], no_wait: false)
  synchronize do
    unless @exclusive_thread == Thread.current
      if busy_for_exclusive?(purpose)
        return false if no_wait

        yield_shares(purpose: purpose, compatible: compatible, block_share: true) do
          wait_for(:start_exclusive) { busy_for_exclusive?(purpose) }
        end
      end
      @exclusive_thread = Thread.current
    end
    @exclusive_depth += 1

    true
  end
end

start_sharing()

來源： 顯示 | 在 GitHub 上

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 113
def start_sharing
  synchronize do
    if @sharing[Thread.current] > 0 || @exclusive_thread == Thread.current
      # We already hold a lock; nothing to wait for
    elsif @waiting[Thread.current]
      # We're nested inside a +yield_shares+ call: we'll resume as
      # soon as there isn't an exclusive lock in our way
      wait_for(:start_sharing) { @exclusive_thread }
    else
      # This is an initial / outermost share call: any outstanding
      # requests for an exclusive lock get to go first
      wait_for(:start_sharing) { busy_for_sharing?(false) }
    end
    @sharing[Thread.current] += 1
  end
end

stop_exclusive(compatible: [])

放棄獨占鎖定。只能呼叫呼叫 start_exclusive 的執行緒 (且目前保有鎖定) 來呼叫。

來源：顯示 | 於 GitHub

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 95
def stop_exclusive(compatible: [])
  synchronize do
    raise "invalid unlock" if @exclusive_thread != Thread.current

    @exclusive_depth -= 1
    if @exclusive_depth == 0
      @exclusive_thread = nil

      if eligible_waiters?(compatible)
        yield_shares(compatible: compatible, block_share: true) do
          wait_for(:stop_exclusive) { @exclusive_thread || eligible_waiters?(compatible) }
        end
      end
      @cv.broadcast
    end
  end
end

stop_sharing()

來源：顯示 | 於 GitHub

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 130
def stop_sharing
  synchronize do
    if @sharing[Thread.current] > 1
      @sharing[Thread.current] -= 1
    else
      @sharing.delete Thread.current
      @cv.broadcast
    end
  end
end

yield_shares(purpose: nil, compatible: [], block_share: false)

執行所提供的區塊時，暫時放棄所有已持有的 Share 鎖，讓任何相容的獨佔鎖要求繼續進行。

來源：顯示 | 於 GitHub

# File activesupport/lib/active_support/concurrency/share_lock.rb, line 170
def yield_shares(purpose: nil, compatible: [], block_share: false)
  loose_shares = previous_wait = nil
  synchronize do
    if loose_shares = @sharing.delete(Thread.current)
      if previous_wait = @waiting[Thread.current]
        purpose = nil unless purpose == previous_wait[0]
        compatible &= previous_wait[1]
      end
      compatible |= [false] unless block_share
      @waiting[Thread.current] = [purpose, compatible]
    end

    @cv.broadcast
  end

  begin
    yield
  ensure
    synchronize do
      wait_for(:yield_shares) { @exclusive_thread && @exclusive_thread != Thread.current }

      if previous_wait
        @waiting[Thread.current] = previous_wait
      else
        @waiting.delete Thread.current
      end
      @sharing[Thread.current] = loose_shares if loose_shares
    end
  end
end