There are multiple reasons to do this. One big reason is the license:
talloc is LGPLv3+, which forces mpv to be licensed as GPLv3+.
Another one is that our talloc copy contains modifications, which makes
it essentially incompatible with upstream talloc (in particular, our
version aborts on out of memory conditions - well, it wasn't my idea).
Updating from upstream is also a bit involved - the talloc source is
not really organized in a way to allow copying it into projects (and
this isn't an intended use-case).
Finally, talloc is kind of big and bloated. The replacement halves the
amount of code - mainly because we didn't use all talloc features. It's
even more extreme if you compare upstream talloc (~4700 lines) and the
new allocator without talloc compat (~900 lines).
The replacement provides all features we need. It also doesn't clash
with talloc. (The talloc compatibility wrapper uses macros to avoid
introducing linker-level symbols which could clash with libtalloc.)
It also tries to lower the overhead (only 4 words opposed to 10 words
in talloc for leaf nodes in release mode). Debugging features like leak
reporting can be enabled at compile time and add somewhat more overhead.
Though I'm not sure whether the overhead reduction was actually
successful: allocations with children need an "extra" header, which adds
plenty of overhead, and it turns out that almost half of all allocations
have children. Maybe the implementation could be simplified and the
extra header removed - even then, overhead would be lower than talloc's.
Currently, debugging features can be entirely deactivated by defining
NDEBUG - I'm not sure if anything defines this directly yet, though.
Unlike in talloc, the leak reporting stuff is thread-safe. (That's also
why it's far less elegant, and requires extra list pointers.)
Comes with a compatibility layer, so no changes to mpv source code
are needed. The idea is that we will pretend to be using talloc for
a while, so that we can revert to our old talloc implementation at
any time for debugging purposes.
Some inspiration was taken from Mesa's ralloc:
http://cgit.freedesktop.org/mesa/mesa/tree/src/glsl/ralloc.h
This is another talloc replacement, but lacks some features we need
(getting size of an allocation, debugging features, being able to
access children in the dtor).
There's some information in ta/README what will happen next and how the
transition is expected to progress.
Change talloc destructor so that they can never signal failure, and
don't return a status code. This makes our talloc copy even more
incompatible to upstream talloc, but on the other hand this is
preparation for getting rid of talloc entirely.
(The talloc replacement in the next commit won't allow the talloc_free
equivalent to fail, and the destructor return value would be useless.
But I don't want to change any mpv code either; the idea is that the
talloc replacement commit can be reverted for some time in order to
test whether the talloc replacement introduced a regression.)
Put MP_EXPAND_ARGS() in compiler.h, even though it's not compiler
dependent. Both mp_talloc.h and mp_common.h need it, while mp_common.h
includes mp_talloc.h. This is the least annoying solution.
Finish renaming directories and moving files. Adjust all include
statements to make the previous commit compile.
The two commits are separate, because git is bad at tracking renames
and content changes at the same time.
Also take this as an opportunity to remove the separation between
"common" and "mplayer" sources in the Makefile. ("common" used to be
shared between mplayer and mencoder.)
MinGW maps the "printf" format string archetype to the non-standard
MSVCRT functions, even if __USE_MINGW_ANSI_STDIO is defined and set
to 1. We need to use "gnu_printf" to use the format strings as provided
by vsnprintf and similar functions to get correct warnings.
Since "gnu_printf" isn't necessarily available on other GCC compatible
compilers (such as clang), do this only on MinGW.
The destructors used by talloc take a "void *" first parameter.
However talloc.h had a #define hack that treated the destructor as a
function taking first parameter of type "typeof(ptr)" where ptr is the
pointer the destructor is set for. I suppose this was done to add some
kind of "type safety" against adding a destructor expecting another
type of pointer; however this hack is questionable and violates the
real C level typing. Remove the hack from the header and adjust
talloc.c to avoid a warning about a C type violation that became
visible after removing the hack.
libsmbclient uses dynamically linked libtalloc.so which has symbols
with names matching those in the internal talloc.c. This name
collision caused a crash under stream_smb when trying to play
anything with smb://. Add a "#pragma GCC visibility" hack to talloc.h
to hide the internal symbols from being visible to the outside
libtalloc.so. Hopefully this doesn't break any platform worse than
possibly causing a compiler warning about an unknown pragma (at least
GCC and clang recognize it).
wm4
Stefano Pigozzi
wm4
Uoti Urpala
Uoti Urpala