The gigantic define_commit_slab() macro repeats the definition of a
static variable that occurs earlier in the macro text. The purpose of
the repeated definition at the end of the macro is that it takes the
semicolon that occurs where the macro is used.
We cannot just remove the first definition of the variable because it
is referenced elsewhere in the macro text, and defining the macro later
would produce undefined identifier errors. We cannot have a "forward"
declaration, either. (This works only with "extern" global variables.)
The solution is to use a declaration of a struct that is already defined
earlier. This language construct can serve the same purpose as the
duplicated static variable definition, but without the confusion.
Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Memory use reduction when commit-slab facility is used to annotate
sparsely (which is not recommended in the first place).
* jc/commit-slab:
commit-slab: introduce slabname##_peek() function
There is no API to ask "Does this commit have associated data in
slab?". If an application wants to (1) parse just a few commits at
the beginning of a process, (2) store data for only these commits,
and then (3) start processing many commits, taking into account the
data stored (for a few of them) in the slab, the application would
use slabname##_at() to allocate a space to store data in (2), but
there is no API other than slabname##_at() to use in step (3). This
allocates and wastes new space for these commits the caller is only
interested in checking if they have data stored in step (2).
Introduce slabname##_peek(), which is similar to slabname##_at() but
returns NULL when there is no data already associated to it in such
a use case.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Callers currently must use init_foo_slab() at runtime before
accessing a slab. For global slabs, it's much nicer if we
can initialize them in BSS, so that each user does not have
to add code to check-and-initialize.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When allocating the slab, the code accidentally computed the array
size from s->slab (an elemtype**). The slab is an array of elemtype*,
however, so we should take the size of *s->slab.
Noticed-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Thomas Rast <tr@thomasrast.ch>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This shuts up compiler warnings about unused functions. No such
warnings are currently triggered, but if someone were to actually
use init_NAME_with_stride() as documented, they would get a warning
about init_NAME() being unused.
While there, write a comment about why the last real declaration of
the variable is without a terminating semicolon, while another
forward declarations have one.
Signed-off-by: Thomas Rast <tr@thomasrast.ch>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The clear_$slabname() function was only documented by source code so
far. Write something about it.
Signed-off-by: Thomas Rast <tr@thomasrast.ch>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The slab initialization code includes the calculation of the
slab 'elem_size', which is in turn used to determine the size
(capacity) of the slab. Each element of the slab represents an
array, of length 'stride', of 'elemtype'. (Note that it may be
clearer if the define_commit_slab macro parameter was called
'basetype' rather than 'elemtype'). However, the 'elem_size'
calculation incorrectly uses 'sizeof(struct slabname)' in the
expression, rather than 'sizeof(elemtype)'.
Within the slab access routine, <slabname>_at(), the given commit
'index' is transformed into an (slab#, slot#) pair used to address
the required element (a pointer to the first element of the array
of 'elemtype' associated with that commit). The current code to
calculate these address coordinates multiplies the commit index
by the 'stride' which, at least for the slab#, produces the wrong
result. Using the commit index directly, without scaling by the
'stride', produces the correct 'logical' address.
Also, when allocating a new slab, the size of the allocation only
allows for a slab containing elements of single element arrays of
'elemtype'. This should allow for elements of an array of length
'stride' of 'elemtype'. In order to fix this, we need to change
the element size parameter to xcalloc() by multiplying the current
element size (sizeof(**s->slab)) by the s->stride.
Having changed the calculation of the slot#, we now need to convert
the logical 'nth_slot', by scaling with s->stride, into the correct
physical address.
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a header file to define a macro that can define the struct
type, initializer, accessor and cleanup functions to manage a commit
slab. Update the "indegree" topological sort facility using it.
To associate 32 flag bits with each commit, you can write:
define_commit_slab(flag32, uint32);
to declare "struct flag32" type, define an instance of it with
struct flag32 flags;
and initialize it by calling
init_flag32(&flags);
After that, a call to flag32_at() function
uint32 *fp = flag32_at(&flags, commit);
will return a pointer pointing at a uint32 for that commit. Once
you are done with these flags, clean them up with
clear_flag32(&flags);
Callers that cannot hard-code how wide the data to be associated
with the commit be at compile time can use the "_with_stride"
variant to initialize the slab.
Suppose you want to give one bit per existing ref, and paint commits
down to find which refs are descendants of each commit. Saying
typedef uint32 bits320[5];
define_commit_slab(flagbits, bits320);
at compile time will still limit your code with hard-coded limit,
because you may find that you have more than 320 refs at runtime.
The code can declare a commit slab "struct flagbits" like this
instead:
define_commit_slab(flagbits, unsigned char);
struct flagbits flags;
and initialize it by:
nrefs = ... count number of refs ...
init_flagbits_with_stride(&flags, (nrefs + 7) / 8);
so that
unsigned char *fp = flagbits_at(&flags, commit);
will return a pointer pointing at an array of 40 "unsigned char"s
associated with the commit, once you figure out nrefs is 320 at
runtime.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
