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Автор SHA1 Сообщение Дата
Junio C Hamano 922ffec6fe Merge branch 'rb/hashmap-h-compilation-fix'
Code clean-up.

* rb/hashmap-h-compilation-fix:
  hashmap.h: remove unused variable
2018-02-13 13:39:10 -08:00
Randall S. Becker 7d68bb0766 hashmap.h: remove unused variable
In 'hashmap_enable_item_counting()', item is assigned but never
used.  This causes a warning on HP NonStop.  As the variable is
never used, fix this by just removing it.

Signed-off-by: Randall S. Becker <rsbecker@nexbridge.com>
Helped-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-01-16 14:27:07 -08:00
Johannes Schindelin 826c778f7c hashmap: adjust documentation to reflect reality
The hashmap API is just complicated enough that even at least one
long-time Git contributor has to look up how to use it every time he
finds a new use case. When that happens, it is really useful if the
provided example code is correct...

While at it, "fix a memory leak", avoid statements before variable
declarations, fix a const -> no-const cast, several %l specifiers (which
want to be %ld), avoid using an undefined constant, call scanf()
correctly, use FLEX_ALLOC_STR() where appropriate, and adjust the style
here and there.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-12-05 13:37:43 -08:00
Jeff Hostetler 8b604d1951 hashmap: add API to disable item counting when threaded
This is to address concerns raised by ThreadSanitizer on the mailing list
about threaded unprotected R/W access to map.size with my previous "disallow
rehash" change (0607e10009).

See:
https://public-inbox.org/git/adb37b70139fd1e2bac18bfd22c8b96683ae18eb.1502780344.git.martin.agren@gmail.com/

Add API to hashmap to disable item counting and thus automatic rehashing.
Also include API to later re-enable them.

When item counting is disabled, the map.size field is invalid.  So to
prevent accidents, the field has been renamed and an accessor function
hashmap_get_size() has been added.  All direct references to this
field have been been updated.  And the name of the field changed
to map.private_size to communicate this.

Here is the relevant output from ThreadSanitizer showing the problem:

WARNING: ThreadSanitizer: data race (pid=10554)
  Read of size 4 at 0x00000082d488 by thread T2 (mutexes: write M16):
    #0 hashmap_add hashmap.c:209
    #1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
    #2 handle_range_dir name-hash.c:347
    #3 handle_range_1 name-hash.c:415
    #4 lazy_dir_thread_proc name-hash.c:471
    #5 <null> <null>

  Previous write of size 4 at 0x00000082d488 by thread T1 (mutexes: write M31):
    #0 hashmap_add hashmap.c:209
    #1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
    #2 handle_range_dir name-hash.c:347
    #3 handle_range_1 name-hash.c:415
    #4 handle_range_dir name-hash.c:380
    #5 handle_range_1 name-hash.c:415
    #6 lazy_dir_thread_proc name-hash.c:471
    #7 <null> <null>

Martin gives instructions for running TSan on test t3008 in this post:
https://public-inbox.org/git/CAN0heSoJDL9pWELD6ciLTmWf-a=oyxe4EXXOmCKvsG5MSuzxsA@mail.gmail.com/

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-07 09:42:02 +09:00
Stefan Beller 1ecbf31d02 hashmap: migrate documentation from Documentation/technical into header
While at it, clarify the use of `key`, `keydata`, `entry_or_key` as well
as documenting the new data pointer for the compare function.

Rework the example.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-06-30 13:11:59 -07:00
Stefan Beller 7663cdc86c hashmap.h: compare function has access to a data field
When using the hashmap a common need is to have access to caller provided
data in the compare function. A couple of times we abuse the keydata field
to pass in the data needed. This happens for example in patch-ids.c.

This patch changes the function signature of the compare function
to have one more void pointer available. The pointer given for each
invocation of the compare function must be defined in the init function
of the hashmap and is just passed through.

Documentation of this new feature is deferred to a later patch.
This is a rather mechanical conversion, just adding the new pass-through
parameter.  However while at it improve the naming of the fields of all
compare functions used by hashmaps by ensuring unused parameters are
prefixed with 'unused_' and naming the parameters what they are (instead
of 'unused' make it 'unused_keydata').

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-06-30 12:49:28 -07:00
Jeff Hostetler 0607e10009 hashmap: add disallow_rehash setting
Teach hashmap to allow rehashes to be suppressed.
This is useful when hashmaps are accessed by multiple
threads.  It still requires the caller to properly
manage their locking.  This just prevents unexpected
rehashing during inserts and deletes.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-03-22 13:41:41 -07:00
Jeff Hostetler f75619bd6d hashmap: allow memihash computation to be continued
Add variant of memihash() to allow the hash computation to
be continued.  There are times when we compute the hash on
a full path and then the hash on just the path to the parent
directory.  This can be expensive on large repositories.

With this, we can hash the parent directory first. And then
continue the computation to include the "/filename".

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-03-22 13:41:41 -07:00
Karsten Blees 7b64d42d22 hashmap: add string interning API
Interning short strings with high probability of duplicates can reduce the
memory footprint and speed up comparisons.

Add strintern() and memintern() APIs that use a hashmap to manage the pool
of unique, interned strings.

Note: strintern(getenv()) could be used to sanitize git's use of getenv(),
in case we ever encounter a platform where a call to getenv() invalidates
previous getenv() results (which is allowed by POSIX).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-07-07 13:56:38 -07:00
Karsten Blees ab73a9d119 hashmap: add simplified hashmap_get_from_hash() API
Hashmap entries are typically looked up by just a key. The hashmap_get()
API expects an initialized entry structure instead, to support compound
keys. This flexibility is currently only needed by find_dir_entry() in
name-hash.c (and compat/win32/fscache.c in the msysgit fork). All other
(currently five) call sites of hashmap_get() have to set up a near emtpy
entry structure, resulting in duplicate code like this:

  struct hashmap_entry keyentry;
  hashmap_entry_init(&keyentry, hash(key));
  return hashmap_get(map, &keyentry, key);

Add a hashmap_get_from_hash() API that allows hashmap lookups by just
specifying the key and its hash code, i.e.:

  return hashmap_get_from_hash(map, hash(key), key);

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-07-07 13:56:35 -07:00
Karsten Blees 039dc71a7c hashmap: factor out getting a hash code from a SHA1
Copying the first bytes of a SHA1 is duplicated in six places,
however, the implications (the actual value would depend on the
endianness of the platform) is documented only once.

Add a properly documented API for this.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-07-07 13:56:24 -07:00
Karsten Blees b6aad99473 hashmap.h: use 'unsigned int' for hash-codes everywhere
Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-02-24 15:26:30 -08:00
Karsten Blees 6a364ced49 add a hashtable implementation that supports O(1) removal
The existing hashtable implementation (in hash.[ch]) uses open addressing
(i.e. resolve hash collisions by distributing entries across the table).
Thus, removal is difficult to implement with less than O(n) complexity.
Resolving collisions of entries with identical hashes (e.g. via chaining)
is left to the client code.

Add a hashtable implementation that supports O(1) removal and is slightly
easier to use due to builtin entry chaining.

Supports all basic operations init, free, get, add, remove and iteration.

Also includes ready-to-use hash functions based on the public domain FNV-1
algorithm (http://www.isthe.com/chongo/tech/comp/fnv).

The per-entry data structure (hashmap_entry) is piggybacked in front of
the client's data structure to save memory. See test-hashmap.c for usage
examples.

The hashtable is resized by a factor of four when 80% full. With these
settings, average memory consumption is about 2/3 of hash.[ch], and
insertion is about twice as fast due to less frequent resizing.

Lookups are also slightly faster, because entries are strictly confined to
their bucket (i.e. no data of other buckets needs to be traversed).

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-11-18 13:03:51 -08:00