Thread overview
Issue with module destructor order
Mar 26, 2012
Benjamin Thaut
Apr 08, 2012
Benjamin Thaut
Apr 08, 2012
Kevin Cox
Apr 08, 2012
Timon Gehr
May 23, 2012
Martin Nowak
May 23, 2012
Martin Nowak
March 26, 2012
Hi,
I came across a issue with the order in which druntime calls the module destructors. I created a small repro case for it:

file a.d:
module a;

import logger;

shared static this()
{
  log("a init");
}

shared static ~this()
{
  log("a deinit");
}

file b.d:
module b;

import mix;

class Foo
{
  mixin logIt;
}

file logger.d:
module logger;

import std.stdio;

shared static this()
{
  writefln("logger init");
}

void log(string message)
{
  writefln(message);
}

shared static ~this()
{
  writefln("logger deinit");
}

file main.d:
module main;


import std.stdio;

import a;

import b;



int main(string[] argv)
{
  auto foo = new Foo();

  writefln("main");

  return 0;

}


mix.d:
module mix;

public import logger;

mixin template logIt()
{
  static shared this()
  {
    log(typeof(this).stringof ~ " init");
  }

  static shared ~this()
  {
    log(typeof(this).stringof ~ " deinit");
  }
}

Compile with: dmd a.d b.d logger.d main.d mix.d -oftest.exe
Running gives the following output:

logger init
a init
shared(Foo) init
main
a deinit
logger deinit
shared(Foo) deinit

That means that the logger module destructor is called before the b module actually gets destructed which leads to the logger beeing used in a destructed state. In my real world case this leads to a fiel operation on a closed file handle. Is this intended behaviour or is this a bug? I assume this happens because of the mixin template and the public import.
I'm using dmd 2.058.

-- 
Kind Regards
Benjamin Thaut
April 08, 2012
Created bug ticket: http://d.puremagic.com/issues/show_bug.cgi?id=7855

-- 
Kind Regards
Benjamin Thaut
April 08, 2012
On Mar 26, 2012 5:11 AM, "Benjamin Thaut" <code@benjamin-thaut.de> wrote:
> Is this intended behaviour or is this a bug? I assume this happens
because of the mixin template and the public import.
> I'm using dmd 2.058.
>
> --
> Kind Regards
> Benjamin Thaut

I don't think the order of destructors is defined. There would be no way to have semantic control because it wouldn't work when you link different files together.  The only solution would be to have the compiler analyse the code and figure out what should be destructed first which would be and impressive feat.

The solution to solving your problem is not to close the file object in the destructor and let the OS clean it up when your program terminates.


April 08, 2012
On 04/08/2012 02:14 PM, Kevin Cox wrote:
>
> On Mar 26, 2012 5:11 AM, "Benjamin Thaut" <code@benjamin-thaut.de
> <mailto:code@benjamin-thaut.de>> wrote:
>  > Is this intended behaviour or is this a bug? I assume this happens
> because of the mixin template and the public import.
>  > I'm using dmd 2.058.
>  >
>  > --
>  > Kind Regards
>  > Benjamin Thaut
>
> I don't think the order of destructors is defined. There would be no way
> to have semantic control because it wouldn't work when you link
> different files together.  The only solution would be to have the
> compiler analyse the code and figure out what should be destructed first
> which would be and impressive feat.
>

Actually that is what is normally done. (it is quite conservative though, cyclical imports where multiple modules have static constructors/destructors are just disallowed and terminate the program on startup.)

> The solution to solving your problem is not to close the file object in
> the destructor and let the OS clean it up when your program terminates.
>

This would be a workaround.
May 23, 2012
> mixin template logIt()
> {
>    static shared this()
>    {
>      log(typeof(this).stringof ~ " init");
>    }
>
>    static shared ~this()
>    {
>      log(typeof(this).stringof ~ " deinit");
>    }
> }
Try "shared static this()" and it won't run as a class constructor.
http://dlang.org/class.html#StaticConstructor
May 23, 2012
> mixin template logIt()
> {
>    static shared this()
>    {
>      log(typeof(this).stringof ~ " init");
>    }
>
>    static shared ~this()
>    {
>      log(typeof(this).stringof ~ " deinit");
>    }
> }
Try "shared static this()" and it won't run as a class constructor.
http://dlang.org/class.html#StaticConstructor