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retain、release 的实现机制是怎样的？ #14

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tbfungeek opened this issue Jan 5, 2020 · 0 comments
Open

retain、release 的实现机制是怎样的？ #14

tbfungeek opened this issue Jan 5, 2020 · 0 comments

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@tbfungeek
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建议查看我的博客网站上的关于《iOS 内存管理之对象创建，销毁，持有，弱引用源码剖析》具体的源码分析。http://coderlin.coding.me/

其实考察的还是 NONEPOINT_ISA 和 SideTables 结构

  • retain的实现机制。
SideTable& table = SideTables()[This];
size_t& refcntStorage = table.refcnts[This];
refcntStorage += SIZE_TABLE_RC_ONE;
  • release的实现机制。
SideTable& table = SideTables()[This];
size_t& refcntStorage = table.refcnts[This];
refcntStorage -= SIZE_TABLE_RC_ONE;

二者的实现机制类似，概括讲就是通过第一层 hash 算法，找到 指针变量 所对应的 sideTable。然后再通过一层 hash 算法，找到存储 引用计数 的 size_t，然后对其进行增减操作。retainCount 不是固定的 1，SIZE_TABLE_RC_ONE 是一个宏定义，实际上是一个值为 4 的偏移量。
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@tbfungeek