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digitalmars.D.learn - Linking D and Obj-C code into a Cocoa app proper? (Mac)

reply Heywood Floyd <soul8o8 gmail.com> writes:
Good Evenening Ladies and Gentlemen!



== Background ==
So I currently have a bare-bones Cocoa-app. It's just a window with an
OpenGL-view. In the view's draw-function I make the gl-view the current OpenGL
context and then call "extern (C) render()". Meanwhile, in a D-file I have the
implementation for this function. Here I've copied all the function names from
opengl.h and declared them in the D-file ("extern (C) glBlabla()" etc) so I can
call glBegin etc from my render()-function in D. This is all in XCode and I use
Michel Fortin's "D for XCode"-plugin btw.

This works great! The window paint triangles and what have you. Pretty!
Happiness!

But, sometimes I get reeeaally weird bugs. I had one bug where if I added an
empty function to a class in D I got EXC_BAD_ACCES (segfault). An empty
function! Ie "void f(){}". Remove the function--it works. In the debugger, I
got the impression maybe the stack has got messed up, but I don't know, the
debugger just shows assembler code, and I don't have the proper skills.

This got really frustrating, needless to say, so I started playing around with
the build settings. I switched from using LLVM 1.5 (for the obj-c code) to gcc
4.2. And now it magically seems to work!

Ok. But as you might understand, the frustration is not quite gone. Adding a
function now feels like a spinning a wheel of fortune. It's utterly
demoralizing. So I thought about this and realized, I probably should try to
find out what it is I'm actually doing here, and hear with some real
programmers if there's a "proper" way of doing it. So my question, dear D
community:



== Question ==
How do you make D code and Obj-C code coexist? That is, I want to write a
Cocoa-app that is mostly written in D, and with a little "glue"-code in
Objective-C. How do you set that up? Is it even supposed to be possible?

(And what could the bug above be? I know LLVM does link-time optimizations, and
even run-time optimizations. Could it be that it messes things up?)



BR
/HF
Oct 05 2010
parent reply Michel Fortin <michel.fortin michelf.com> writes:
On 2010-10-05 10:02:45 -0400, Heywood Floyd <soul8o8 gmail.com> said:


 But, sometimes I get reeeaally weird bugs. I had one bug where if I 
 added an empty function to a class in D I got EXC_BAD_ACCES (segfault). 
 An empty function! Ie "void f(){}". Remove the function--it works. In 
 the debugger, I got the impression maybe the stack has got messed up, 
 but I don't know, the debugger just shows assembler code, and I don't 
 have the proper skills.


It's hard to say without further details, but it could be that you're 
not recompiling everything that uses the class where you add a 
function. Unlike in Objective-C, adding a function to a D class breaks 
most compiled code that uses that class (because you're adding an 
offset to the virtual function table), so you need to recompile every D 
module that uses that class (or a derived class).

Note that this is totally unrelated to having Objective-C code in the 
same program.



 This got really frustrating, needless to say, so I started playing 
 around with the build settings. I switched from using LLVM 1.5 (for the 
 obj-c code) to gcc 4.2. And now it magically seems to work!


Are you using D for Xcode? By doing that you basically force everything 
to be recompiled, which solves problem described above.



 [...]
 
 == Question ==
 How do you make D code and Obj-C code coexist? That is, I want to write 
 a Cocoa-app that is mostly written in D, and with a little "glue"-code 
 in Objective-C. How do you set that up? Is it even supposed to be 
 possible?


It is totally possible, and not that hard. Communicating via `extern 
(C)` functions should work well.



 (And what could the bug above be? I know LLVM does link-time 
 optimizations, and even run-time optimizations. Could it be that it 
 messes things up?)


I doubt LLVM optimizations have anything to do with your problem. 
Things to keep in mind when mixing Objective-C:

1. Apple's Objective-C GC isn't supported by D, so you it's probably 
safer to use manual memory management (retain/release) on the 
Objective-C site.

2. Exceptions are not compatible between the two runtimes. Throwing can 
cause unexpected results when it unwinds stack frames in the other 
language.


-- 
Michel Fortin
michel.fortin michelf.com
http://michelf.com/
Oct 05 2010
parent Heywood Floyd <soul8o8 gmail.com> writes:
Ok! Thanks for the advice! Great work on the plugin—it got me into D :)

/FH

Michel Fortin Wrote:


 On 2010-10-05 10:02:45 -0400, Heywood Floyd <soul8o8 gmail.com> said:
 

 But, sometimes I get reeeaally weird bugs. I had one bug where if I 
 added an empty function to a class in D I got EXC_BAD_ACCES (segfault). 
 An empty function! Ie "void f(){}". Remove the function--it works. In 
 the debugger, I got the impression maybe the stack has got messed up, 
 but I don't know, the debugger just shows assembler code, and I don't 
 have the proper skills.


 
 It's hard to say without further details, but it could be that you're 
 not recompiling everything that uses the class where you add a 
 function. Unlike in Objective-C, adding a function to a D class breaks 
 most compiled code that uses that class (because you're adding an 
 offset to the virtual function table), so you need to recompile every D 
 module that uses that class (or a derived class).
 
 Note that this is totally unrelated to having Objective-C code in the 
 same program.
 
 

 This got really frustrating, needless to say, so I started playing 
 around with the build settings. I switched from using LLVM 1.5 (for the 
 obj-c code) to gcc 4.2. And now it magically seems to work!


 
 Are you using D for Xcode? By doing that you basically force everything 
 to be recompiled, which solves problem described above.
 
 

 [...]
 
 == Question ==
 How do you make D code and Obj-C code coexist? That is, I want to write 
 a Cocoa-app that is mostly written in D, and with a little "glue"-code 
 in Objective-C. How do you set that up? Is it even supposed to be 
 possible?


 
 It is totally possible, and not that hard. Communicating via `extern 
 (C)` functions should work well.
 
 

 (And what could the bug above be? I know LLVM does link-time 
 optimizations, and even run-time optimizations. Could it be that it 
 messes things up?)


 
 I doubt LLVM optimizations have anything to do with your problem. 
 Things to keep in mind when mixing Objective-C:
 
 1. Apple's Objective-C GC isn't supported by D, so you it's probably 
 safer to use manual memory management (retain/release) on the 
 Objective-C site.
 
 2. Exceptions are not compatible between the two runtimes. Throwing can 
 cause unexpected results when it unwinds stack frames in the other 
 language.
 
 
 -- 
 Michel Fortin
 michel.fortin michelf.com
 http://michelf.com/
Oct 05 2010