Add a function for building a string, printf style, using a memory pool.
It uses the free space in the current block in the first attempt. If
that suffices then the result can already be used without copying or
reformatting.
For strings that are significantly shorter on average than the block
size (ca. 1 MiB by default) this is the case most of the time, leading
to a better perfomance than a solution that doesn't access mem-pool
internals.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
About half the function declarations in mem-pool.h used 'struct mem_pool
*pool', while the other half used 'struct mem_pool *mem_pool'. Make the
code a bit more consistent by just using 'pool' in preference to
'mem_pool' everywhere.
No behavioral changes included; this is just a mechanical rename (though
a line or two was rewrapped as well).
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A typical memory type, such as strbuf, hashmap, or string_list can be
stored on the stack or embedded within another structure. mem_pool
cannot be, because of how mem_pool_init() and mem_pool_discard() are
written. mem_pool_init() does essentially the following (simplified
for purposes of explanation here):
void mem_pool_init(struct mem_pool **pool...)
{
*pool = xcalloc(1, sizeof(*pool));
It seems weird to require that mem_pools can only be accessed through a
pointer. It also seems slightly dangerous: unlike strbuf_release() or
strbuf_reset() or string_list_clear(), all of which put the data
structure into a state where it can be re-used after the call,
mem_pool_discard(pool) will leave pool pointing at free'd memory.
read-cache (and split-index) are the only current users of mem_pools,
and they haven't fallen into a use-after-free mistake here, but it seems
likely to be problematic for future users especially since several of
the current callers of mem_pool_init() will only call it when the
mem_pool* is not already allocated (i.e. is NULL).
This type of mechanism also prevents finding synchronization
points where one can free existing memory and then resume more
operations. It would be natural at such points to run something like
mem_pool_discard(pool...);
and, if necessary,
mem_pool_init(&pool...);
and then carry on continuing to use the pool. However, this fails badly
if several objects had a copy of the value of pool from before these
commands; in such a case, those objects won't get the updated value of
pool that mem_pool_init() overwrites pool with and they'll all instead
be reading and writing from free'd memory.
Modify mem_pool_init()/mem_pool_discard() to behave more like
strbuf_init()/strbuf_release()
or
string_list_init()/string_list_clear()
In particular: (1) make mem_pool_init() just take a mem_pool* and have
it only worry about allocating struct mp_blocks, not the struct mem_pool
itself, (2) make mem_pool_discard() free the memory that the pool was
responsible for, but leave it in a state where it can be used to
allocate more memory afterward (without the need to call mem_pool_init()
again).
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
fast-import had a special mem_pool_strdup() convenience function that I
want to be able to use from the new merge algorithm I am writing. Move
it from fast-import to mem-pool, and also add a mem_pool_strndup()
while at it that I also want to use.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add an option (controlled by an environment variable) perform extra
validations on mem_pool allocated cache entries. When set:
1) Invalidate cache_entry memory when discarding cache_entry.
2) When discarding index_state struct, verify that all cache_entries
were allocated from expected mem_pool.
3) When discarding mem_pools, invalidate mem_pool memory.
This should provide extra checks that mem_pools and their allocated
cache_entries are being used as expected.
Signed-off-by: Jameson Miller <jamill@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add functions for:
- combining two memory pools
- determining if a memory address is within the range managed by a
memory pool
These functions will be used by future commits.
Signed-off-by: Jameson Miller <jamill@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add initialization and discard functions to mem_pool type. As the
memory allocated by mem_pool can now be freed, we also track the large
allocations.
If the there are existing mp_blocks in the mem_poo's linked list of
mp_blocksl, then the mp_block for a large allocation is inserted
behind the head block. This is because only the head mp_block is considered
when searching for availble space. This results in the following
desirable properties:
1) The mp_block allocated for the large request will not be included
not included in the search for available in future requests, the large
mp_block is sized for the specific request and does not contain any
spare space.
2) The head mp_block will not bumped from considation for future
memory requests just because a request for a large chunk of memory
came in.
These changes are in preparation for a future commit that will utilize
creating and discarding memory pool.
Signed-off-by: Jameson Miller <jamill@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This moves the reusable parts of the memory pool logic used by
fast-import.c into its own file for use by other components.
Signed-off-by: Jameson Miller <jamill@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
