Experimental Physics and Industrial Control System
On 02.11.2017 11:18, Ralph Lange wrote:
Hi Dirk,
On Thu, Nov 2, 2017 at 10:23 AM, Dirk Zimoch <[email protected]
<mailto:[email protected]>> wrote:
[...] I also opt for binary backward compatibility, so that it is
always possible to replace a dynamic library with a newer version
without needing to re-build all programs. Forcing a program to link
only with a very specific library version is, in my opinion, not
very maintenance friendly.
As you seem to have experience with that: which tools / methodology do
you suggest to detect and track ABI changes in libraries, especially
libraries created from C++ sources?
Thanks,
~Ralph
I don't know any tools to support compatibility checks, but here is what
I try to do:
* Never remove API functions (declaring them depreciated is OK)
* Never change the signature of an existing (extern C) function (...in
an incompatible way. Signedness change is often OK. Adding const or
volatile where appropriate is also often OK. Changing 32 bit args (like
int) to potentially 64 bit args (e.g. size_t) is only OK if no 64 bit
was supported previously, but that is already ancient history.)
* Never change the semantics of an existing function (e.g. swap src and
dest parameters in some copy function)
* Never remove, re-order, or change size of the fields of a structure
that is used in an API.
* Add new fields only ever at the end of structure passed to API
functions by reference (and then handle cases gracefully where the
fields don't exist).
* Never remove or re-order virtual methods (the same for non-C++
function tables like in asyn).
* Expose as little as possible in the API. Not all functions are API
functions, not all structures/classes are used in the API. Not all
Macros are part of the API. Keep public and private header files
separate. Do not install private headers. This allows to change any non
API function, class, etc. at any time without breaking the API.
* Do not put private fields/methods in API classes. If private members
are needed, inherit from a API base class without private members. APIs
are not private.
As it is often not feasible to be so strictly backward compatible, I
suggest (any use in my software) the following rules:
* A version consists of 3 numbers: major.minor.patch
* Whenever a change is not binary backward compatible, the major number
increases.
* Whenever there are new features, the minor number increases.
* Whenever a bug is fixed without a new feature, the patch number
increases. (A bugfix may be incompatible in so far that the
incompatibility was the actual bug that has been fixed.)
* In linking use the major number in the file name to ensure no
incompatible version can be used.
* Do not use the minor number or patch number in linking in order to
allow upgrading the library.
See also how Linux (or GNU) does it: /bin/bash on my computer is linked
to libtinfo.so.5 which is a symbolic link to libtinfo.so.5.7. Note that
is is not linked to version 5.7 but only to version 5. This allows to
upgrade the library to 5.8 but not to 6.0 without having to rebuild the
executable.
Or: softIoc on my computer is linked to libstdc++.so.6 which is a
symbolic link to libstdc++.so.6.0.13.
I have no idea how to automatically check for backward compatibility
when releasing a new version. I can imagine checking function and
structure/class signatures automatically. But how to check for semantic
changes?
Dirk
- Replies:
- Re: exporting module versions Mark Rivers
- RE: exporting module versions Mark Rivers
- References:
- exporting module versions Michael Davidsaver
- Re: exporting module versions Andrew Johnson
- Re: exporting module versions Dirk Zimoch
- Re: exporting module versions Ralph Lange
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