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* hashmap: add API to disable item counting when threadedjh/hashmap-disable-countingJeff Hostetler2017-09-071-9/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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 (0607e10009ee4e37cb49b4cec8d28a9dda1656a4). 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>
* hashmap.h: compare function has access to a data fieldStefan Beller2017-06-301-5/+12
| | | | | | | | | | | | | | | | | | | | | 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>
* hashmap: add disallow_rehash settingJeff Hostetler2017-03-221-1/+11
| | | | | | | | | | | 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>
* hashmap: allow memihash computation to be continuedJeff Hostetler2017-03-221-0/+17
| | | | | | | | | | | | | 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>
* convert trivial cases to FLEX_ARRAY macrosJeff King2016-02-221-2/+1
| | | | | | | | | | Using FLEX_ARRAY macros reduces the amount of manual computation size we have to do. It also ensures we don't overflow size_t, and it makes sure we write the same number of bytes that we allocated. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
* hashmap: add string interning APIkb/hashmap-updatesKarsten Blees2014-07-071-0/+38
| | | | | | | | | | | | | | | 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>
* add a hashtable implementation that supports O(1) removalKarsten Blees2013-11-181-0/+228
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>