Tcl 内存管理

Question

我在一些文章中看到过 Tcl 使用引用计数来进行垃圾收集。我想知道这意味着什么，因为据我所知，Tcl 没有指针或引用，所以每个变量只被引用一次。那么它到底在计算什么呢？

Answer 1

这个想法是 Tcl 对值而不是变量进行引用计数。

让我们引用 the wiki page on copy-on-write semantics :

Each value (Tcl_Obj) has a reference count. Whenever the value is passed to a command or assigned to a variable the reference count is incremented and no copy is made. When a value is to be changed the implementation first checks the reference count. If the count is 1 then there is no other reference to the value and it can be changed in place. If the count is greater than 1 then there are other references to this value. If the value were to be changed in place then those references would also be changed. To prevent this a copy of the value is made (with new reference count of 1) and the copy is changed in place.

这个解释中唯一缺少的是，当一个值的引用计数下降到 belov 1 时，该值被销毁。

有关核心信息，请阅读 Tcl_Obj manual page 的“对象的存储管理”部分和 these discussions .