java - 并发包下面类的一些疑问

问题描述

问 题

下面一些注释摘自AbstractQueuedSynchronizer.Node：

/**

• Status field, taking on only the values:

• SIGNAL: The successor of this node is (or will soon be)

• blocked (via park), so the current node must

• unpark its successor when it releases or

• 1. To avoid races, acquire methods must

• first indicate they need a signal,

• then retry the atomic acquire, and then,

• on failure, block.

• CANCELLED: This node is cancelled due to timeout or interrupt.

• Nodes never leave this state. In particular,

• a thread with cancelled node never again blocks.

• CONDITION: This node is currently on a condition queue.

• It will not be used as a sync queue node

• until transferred, at which time the status

• will be set to 0. (Use of this value here has

• nothing to do with the other uses of the

• field, but simplifies mechanics.)

• PROPAGATE: A releaseShared should be propagated to other

• 1. This is set (for head node only) in

• doReleaseShared to ensure propagation

• continues, even if other operations have

• since intervened.

• 0: None of the above
  *

• The values are arranged numerically to simplify use.

• Non-negative values mean that a node doesn't need to

• 1. So, most code doesn't need to check for particular

• values, just for sign.
  *

• The field is initialized to 0 for normal sync nodes, and

• CONDITION for condition nodes. It is modified using CAS

• (or when possible, unconditional volatile writes).

  但是这些状态（粗体）都比较抽象，有比较直白的解释么？或者需要什么知识点才能看懂这些含义

解决方案

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