Jeff King <peff@xxxxxxxx> writes:
> On Thu, May 14, 2015 at 03:25:33PM -0700, Junio C Hamano wrote:
>
>> @@ -90,6 +97,8 @@ static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
>> \
>> if (s->slab_count <= nth_slab) { \
>> int i; \
>> + if (!add_if_missing) \
>> + return NULL; \
>> s->slab = xrealloc(s->slab, \
>> (nth_slab + 1) * sizeof(*s->slab)); \
>> stat_ ##slabname## realloc++; \
>
> This skips extending the list of slabs if we would go past the nth slab.
> But we don't fill in each slab in the first place. I.e., we may have 10
> slabs, but only s->slab[10] is non-NULL.
>
> A few lines below this, we xcalloc() it if necessary. I think that needs
> to respect add_if_missing, as well.
Yup, thanks.
>
>> void unuse_commit_buffer(const struct commit *commit, const void *buffer)
>> {
>> - struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
>> - if (v->buffer != buffer)
>> + struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
>> + if (v && v->buffer != buffer)
>> free((void *)buffer);
>> }
>
> I think you want:
>
> if (!v || v->buffer != buffer)
>
> here. IOW, we free it only if it is not our cached buffer, and it cannot
> be if we do not have a cached buffer. It may be easier to read by
> flipping the logic:
>
> if (v && v->buffer == buffer)
> return; /* it is saved in the cache */
> free((void *)buffer);
>
> Or some variation on that.
I ended up doing it as a variant of the latter, "free unless we have
v->buffer pointing at it".
Sorry for a long delay.
-- >8 --
Subject: [PATCH] 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 wasts 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@xxxxxxxx>
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
commit-slab.h | 34 +++++++++++++++++++++++++++++-----
commit.c | 28 ++++++++++++++++++++--------
2 files changed, 49 insertions(+), 13 deletions(-)
diff --git a/commit-slab.h b/commit-slab.h
index 375c9c7..9d12ce2 100644
--- a/commit-slab.h
+++ b/commit-slab.h
@@ -15,7 +15,13 @@
* - int *indegree_at(struct indegree *, struct commit *);
*
* This function locates the data associated with the given commit in
- * the indegree slab, and returns the pointer to it.
+ * the indegree slab, and returns the pointer to it. The location to
+ * store the data is allocated as necessary.
+ *
+ * - int *indegree_peek(struct indegree *, struct commit *);
+ *
+ * This function is similar to indegree_at(), but it will return NULL
+ * until a call to indegree_at() was made for the commit.
*
* - void init_indegree(struct indegree *);
* void init_indegree_with_stride(struct indegree *, int);
@@ -80,8 +86,9 @@ static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s) \
s->slab = NULL; \
} \
\
-static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
- const struct commit *c) \
+static MAYBE_UNUSED elemtype *slabname## _at_peek(struct slabname *s, \
+ const struct commit *c, \
+ int add_if_missing) \
{ \
int nth_slab, nth_slot; \
\
@@ -90,6 +97,8 @@ static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
\
if (s->slab_count <= nth_slab) { \
int i; \
+ if (!add_if_missing) \
+ return NULL; \
s->slab = xrealloc(s->slab, \
(nth_slab + 1) * sizeof(*s->slab)); \
stat_ ##slabname## realloc++; \
@@ -97,10 +106,25 @@ static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
s->slab[i] = NULL; \
s->slab_count = nth_slab + 1; \
} \
- if (!s->slab[nth_slab]) \
+ if (!s->slab[nth_slab]) { \
+ if (!add_if_missing) \
+ return NULL; \
s->slab[nth_slab] = xcalloc(s->slab_size, \
sizeof(**s->slab) * s->stride); \
- return &s->slab[nth_slab][nth_slot * s->stride]; \
+ } \
+ return &s->slab[nth_slab][nth_slot * s->stride]; \
+} \
+ \
+static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
+ const struct commit *c) \
+{ \
+ return slabname##_at_peek(s, c, 1); \
+} \
+ \
+static MAYBE_UNUSED elemtype *slabname## _peek(struct slabname *s, \
+ const struct commit *c) \
+{ \
+ return slabname##_at_peek(s, c, 0); \
} \
\
static int stat_ ##slabname## realloc
diff --git a/commit.c b/commit.c
index 65179f9..5fb9496 100644
--- a/commit.c
+++ b/commit.c
@@ -244,7 +244,12 @@ void set_commit_buffer(struct commit *commit, void *buffer, unsigned long size)
const void *get_cached_commit_buffer(const struct commit *commit, unsigned long *sizep)
{
- struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+ struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
+ if (!v) {
+ if (sizep)
+ *sizep = 0;
+ return NULL;
+ }
if (sizep)
*sizep = v->size;
return v->buffer;
@@ -271,24 +276,31 @@ const void *get_commit_buffer(const struct commit *commit, unsigned long *sizep)
void unuse_commit_buffer(const struct commit *commit, const void *buffer)
{
- struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
- if (v->buffer != buffer)
+ struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
+ if (!(v && v->buffer == buffer))
free((void *)buffer);
}
void free_commit_buffer(struct commit *commit)
{
- struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
- free(v->buffer);
- v->buffer = NULL;
- v->size = 0;
+ struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
+ if (v) {
+ free(v->buffer);
+ v->buffer = NULL;
+ v->size = 0;
+ }
}
const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
{
- struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+ struct commit_buffer *v = buffer_slab_peek(&buffer_slab, commit);
void *ret;
+ if (!v) {
+ if (sizep)
+ *sizep = 0;
+ return NULL;
+ }
ret = v->buffer;
if (sizep)
*sizep = v->size;
--
2.4.1-449-g1f6c7df
--
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