[Tcl-bugs] [ tcl-Feature Requests-1685436 ] document Tcl_Preserve-ability

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Feature Requests item #1685436, was opened at 2007-03-21 11:22
Message generated for change (Comment added) made by andreas_kupries
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Don Porter (dgp)
Assigned to: Nobody/Anonymous (nobody)
Summary: document Tcl_Preserve-ability

Initial Comment:

Some public Tcl routines return
pointers that can be Tcl_Preserve()d;
for example, Tcl_CreateInterp().

Other public Tcl routines return
pointers that cannot be
Tcl_Preserve()d; for example,
Tcl_CreateNamespace().  The pointers
returned by such routines really
can't be reliably kept long-term.
Perhaps that's a bug, and more
return-able pointers need to support
Tcl_Preserve-ability.  If not, the
documentation should at least make
this distinction clear.






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>Comment By: Andreas Kupries (andreas_kupries)
Date: 2007-03-21 14:10

Message:
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I wonder if we can snarf ideas from the linux kernel for that. IIRC they
are using special macros and type magic, likely gcc specific, to give
pointers additional attributes which the compiler can check. For us
basically a preserve-ability tag which goes with the pointer and is checker
at compile time when Tcl_Preserve is used. I should note that I have no
actual idea how their stuff works in detail. Regarding it being gcc
specific, it should be easy to disable that for other compilers through
redefinition of whatever macros are used to implement this.

Even if we are unable or unwilling to reproduce the thing we can still use
macros like

    #define PRESERVABLE(x) x

to at least add appropriate tags in the sources. No compiler checks, but
at least semi-documentation in the code.


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