kernel/git - git - PowerEL Git System

Tree: 2cfe2a7878

Author	SHA1	Message	Date
Jeff King	e8f91e3df8	prio-queue: make output stable with respect to insertion If two items are added to a prio_queue and compare equal, they currently come out in an apparently random order (this order is deterministic for a particular sequence of insertions and removals, but does not necessarily match the insertion order). This makes it unlike using a date-ordered commit_list, which is one of the main types we would like to replace with it (because prio_queue does not suffer from O(n) insertions). We can make the priority queue stable by keeping an insertion counter for each element, and using it to break ties. This does increase the memory usage of the structure (one int per element), but in practice it does not seem to affect runtime. A best-of-five "git rev-list --topo-order" on linux.git showed less than 1% difference (well within the run-to-run noise). In an ideal world, we would offer both stable and unstable priority queues (the latter to try to maximize performance). However, given the lack of a measurable performance difference, it is not worth the extra code. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>	11 years ago
Jeff King	6d63baa478	prio-queue: factor out compare and swap operations When manipulating the priority queue's heap, we frequently have to compare and swap heap entries. As we are storing only void pointers right now, this is quite easy to do inline in a few lines. However, when we start using a more complicated heap entry in a future patch, that will get longer. Factoring out these operations lets us make future changes in one place. It also makes the code a little shorter and more readable. Note that we actually accept indices into the queue array instead of pointers. This is slightly less flexible than passing pointers-to-pointers (we could not swap items from unrelated arrays, but we would not want to), but will make further refactoring simpler (and lets us avoid repeating "queue->array" at each callsite, which led to some long lines). And finally, note that we are cleaning up an accidental use of a "struct commit" pointer to hold a temporary entry during swap. Even though we currently only use this code for commits, it is supposed to be type-agnostic. In practice this didn't matter anyway because we never dereferenced the commit pointer (and on most systems, the pointer values themselves are interchangeable between types). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>	11 years ago
Junio C Hamano	da24b1044f	sort-in-topological-order: use prio-queue Use the prio-queue data structure to implement a priority queue of commits sorted by committer date, when handling --date-order. The structure can also be used as a simple LIFO stack, which is a good match for --topo-order processing. Signed-off-by: Junio C Hamano <gitster@pobox.com>	12 years ago
Junio C Hamano	b4b594a315	prio-queue: priority queue of pointers to structs Traditionally we used a singly linked list of commits to hold a set of in-flight commits while traversing history. The most typical use of the list is to add commits that are newly discovered to it, keep the list sorted by commit timestamp, pick up the newest one from the list, and keep digging. The cost of keeping the singly linked list sorted is nontrivial, and this typical use pattern better matches a priority queue. Introduce a prio-queue structure, that can be used either as a LIFO stack, or a priority queue. This will be used in the next patch to hold in-flight commits during sort-in-topological-order. Tests and the idea to make it usable for any "void *" pointers to "things" are by Jeff King. Bugs are mine. Signed-off-by: Junio C Hamano <gitster@pobox.com>	12 years ago