在Julia中编写模块finalize方法的正确方法是什么?

问题描述：

我正在尝试找到在Julia中使用 finalizers 的正确方法

I am trying to find the right way to use finalizers in Julia

请参阅Julia文档:

Refer to Julia documentation:

finalizer(x，函数)

finalizer(x, function)

注册没有对x的程序可访问引用时要调用的函数f(x).如果x是位类型，则此函数的行为不可预测.

Register a function f(x) to be called when there are no program-accessible references to x. The behavior of this function is unpredictable if x is of a bits type.

首先，我使用TestModule.jl生成了一个TestModule标准包

First I genetated a TestModule standard package with a TestModule.jl

#in TestModule.jl
module TestModule
end
finalizer(TestModule,(t)->println("fin"))

以及runtest.jl

and also a runtest.jl

#in runtest.jl
using Base.Test
using TestModule

然后我尝试测试Package，但在通过测试时收到错误消息:

then I tried to test Package but I received ERROR while the test was passed:

julia> Pkg.test("TestModule")
INFO: Testing TestModule
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
jl_uv_writecb() ERROR: bad file descriptor EBADF
INFO: TestModule tests passed

之后，我安排了另一个测试用例

after that I arranged another test case

julia> workspace() # new workspace

julia> typeof(TestModule) # make sure *there are no program-accessible references to `TestModule`*

ERROR: UndefVarError: TestModule not defined

julia> using TestModule

julia> finalize(TestModule)  
fin  # finalize method is working 

julia> typeof(TestModule) 
Module #  make sure *there is program-accessible reference to `TestModule`*

julia> workspace() # force clear references 

julia> typeof(TestModule) # check that *there are no program-accessible references*
ERROR: UndefVarError: TestModule not defined

根据上述测试用例，我有一些疑问

According to above test cases I have some questions

为什么在测试过程中为TestModule添加这种finalize方法会产生错误?
为什么在清除引用时未调用finalize方法
为模块添加finalize方法的正确方法是什么

Why adding such finalize method for TestModule generates ERROR during test process?
Why finalize method was not called while I clear references
What is the right way to add finalize method for a module

(OS = Ubuntu，Julia版本= 0.4.0)

(OS=Ubuntu , Julia Version=0.4.0)

编辑

，在workspace()之后也调用gc()也是没有帮助的.

as @Maciek have mentioned, calling gc() after workspace() also, do not help.

谢谢

答

恕我直言，workspace没有任何障碍，并且finalizer仅在用户定义的类型和复合类型上有效.

IMHO, workspace takes no prisoners and in addition the finalizer works well only on user-defined and composite types.

我已经进行了一些测试.看看我的结果:

I've performed some tests. Have a look at my results:

julia> type Foo
         x
         Foo(x) = begin obj = new(x); finalizer(obj,(o) -> println("The end.")); return obj end
       end

julia> Foo(1)

julia> workspace()

julia> gc()
Module the end.error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")
The end.error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")

另一个对象定义在模块范围内的测试:

Another test with object defined inside module scope:

julia> module FinMod

        type T  
            x::Int  
        end

        finalizer(T(1), (t) -> println("Module the end."))
       end
FinMod

julia> FinMod
FinMod

julia> workspace()

julia> gc()
Module the end.error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")

函数(一流的对象)呢?

What about functions(first-class objects)?

julia> function foo()  println("I'm foo") end
foo (generic function with 1 method)

julia> finalizer(foo, (f) -> println("foo function is dead now."))

julia> foo
foo (generic function with 1 method)

julia> workspace()

julia> foo
ERROR: UndefVarError: foo not defined

julia> gc()

julia> #nothing happened

因此，总结一下:我认为workspace不会调用finalize. finalizer函数仅对用户定义的类型和复合类型有效.它不适用于Module或Function.

So, to summarize: In my opinion workspace doesn't call finalize. The finalizer function works OK only for user-defined and composite types. It does not work for Module or Function.

更新:我记得workspace将以前的Main模块重写为LastMain.因此，即使我们的模块不能从Main进入，也仍然可以在LastMain范围内使用(与我上面使用的功能相同).

Update: I remembered that workspace rewrites previous Main module into LastMain. So even if our module is not accesible from Main it's is still alive inside LastMain scope (the same works for the function which I used above).

在Julia中编写模块finalize方法的正确方法是什么?

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