When we have a buffer that we want to grow exponentially with
nm_utils_get_next_realloc_size(), then there are certain buffer
sizes that are better suited.
For example, if you have an empty NMStrBuf (len == 0), and you
want to allocate roughly one kilobyte, then 1024 is a bad choice,
because nm_utils_get_next_realloc_size() will give you 2024 bytes.
NM_UTILS_GET_NEXT_REALLOC_SIZE_1000 might be better in this case.
When growing a buffer by appending a previously unknown number
of elements, the often preferable strategy is growing it exponentially,
so that the amortized runtime and re-allocation costs scale linearly.
GString just always increases the buffer length to the next power of
two. That works.
I think there is value in trying to find an optimal next size. Because
while it doesn't matter in terms of asymptotic behavior, in practice
a better choice should make a difference. This is inspired by what QT
does ([1]), to take more care when growing the buffers:
- QString allocates 4 characters at a time until it reaches size 20.
- From 20 to 4084, it advances by doubling the size each time. More
precisely, it advances to the next power of two, minus 12. (Some memory
allocators perform worst when requested exact powers of two, because
they use a few bytes per block for book-keeping.)
- From 4084 on, it advances by blocks of 2048 characters (4096 bytes).
This makes sense because modern operating systems don't copy the entire
data when reallocating a buffer; the physical memory pages are simply
reordered, and only the data on the first and last pages actually needs
to be copied.
Note that a QT is talking about 12 characters, so we use 24 bytes
head room.
[1] https://doc.qt.io/qt-5/containers.html#growth-strategies
NMTST_SWAP() used memcpy() for copying the value, while NM_SWAP() uses
a temporary variable with typeof(). I think the latter is preferable.
Also, the macro is essentially doing the same thing.
Several macros are used to define function. They had a "_STATIC" variant,
to define the function as static.
I think those macros should not try to abstract entirely what they do.
They should not accept the function scope as argument (or have two
variants per scope). This also because it might make sense to add
additional __attribute__(()) to the function. That only works, if
the macro does not pretend to *not* define a plain function.
Instead, embrace what the function does and let the users place the
function scope as they see fit.
This also follows what is already done with
static NM_CACHED_QUARK_FCN ("autoconnect-root", autoconnect_root_quark)
The abbreviations "ns" and "ms" seem not very clear to me. Spell them
out to nsec/msec. Also, in parts we already used the longer abbreviations,
so it wasn't consistent.
"shared/nm-utils" got long renamed and split into separate parts. The remaining
tests are really to test nm-std-aux and nm-glib-aux (no libnm dependencies). Move
the tests to the appropriate place.
