Eksempel: omskrivning af historien
Følgende situation opstår af og til i modne projekter. Med udgangspunkt i en
stabil branch (ofte kaldet master) begynder man at arbejde på en ny feature
branch (opkaldt efter den pågældende feature). Efter noget tid er den nye
funktionalitet færdigudviklet og klar til at blive merget ind i den stabile
branch. En simpel git merge er ofte alt, hvad der skal til, og hvis
feature-branchen kun har tilføjet funktionalitet og ikke ændret noget ved det
eksisterende, er merge conflicts sjældne.
Det hænder dog, at den nye feature kræver ændringer i kernefunktionaliteten.
Hvis denne funktionalitet udvikles i master-branchen, er en merge fra
master ind i feature-branchen nødvendig inden udviklingen kan fortsætte.
Efter den endelige merge tilbage ind i den stabile branch, kan situationen se
sådan her ud. Bemærk, at feature-branchen hedder parallel2, og den stabile
branch hedder pipelining.
* 456d75f (HEAD, pipelining) Merge branch 'parallel2' into pipelining |\ | * 34dca68 (origin/parallel2, parallel2) Add ut-pipelining parallel_step | * 004e459 Support step() in parallelized pipelines. | * e7c8378 Add note about item_type in parallel.h | * 9943b9e Strengthen parallel code, such that it does not require the number of items | * ea55f36 Add TODO in parallel | * 2384687 Merge branch 'pipelining' into parallel2 | |\ | * \ 703e434 Merge branch 'pipelining' into parallel2 | |\ \ | * | | d415186 Change parallel and parallel_ordered test parameters | * | | 9372b9c Add progress indicator to parallel test and change default modulus | * | | 2a1b9d4 More work on parallelism framework. | * | | a7b100c Fix ut-pipelining sequence generator/verifier | * | | e2b8a43 Add class-level documentation to parallel pipelining stuff | * | | 2055d48 Implement parallel pipelining processing as a library functionality * | | | ebc963d (origin/pipelining) Gather pipelining documentation into a single document * | | | b0e0830 Simplify Graham scan code by using less templates * | | | 39c109c Use class keyword in pipelining when appropriate. * | | | 3f59291 fixup! Replace old convex hull app with new pipelining convex hull app * | | | c756184 Replace old convex hull app with new pipelining convex hull app | |_|/ |/| | * | | 4422a60 Add iterators tests to CMakeLists * | | f652286 Call pipe_segment::end() in actor order. * | | 4b3f9c0 Use push_input_iterator in pipelining2 * | | 016bf6f Add typed_push_output_iterators, for output iterators like ostream_iterator that define value_type to be void (why?) | |/ |/| * | e888bc2 Make sorter forward number of items in output * | 6c60ab5 Fix memory overusage in pipelining * | 2fdaf91 Fix merge sorter crash when evacuating in internal reporting mode with no elements to sort * | 007776f Add ut-pipelining sorttrivial test to test sorting sequences of length 0, 1 and 2 |/ * dad266a Fix struct/class warning
Det har undervejs i udviklingen været nødvendigt med to merges fra stable til feature. Det ser dog ikke så pænt ud i historikken.
Vores mål er at erstatte de to undervejs merges med en enkelt merge med
origin/pipelining.
Det gøres således:
$ git checkout parallel2 Switched to branch 'parallel2' $ git reset --hard 2384687 HEAD is now at 2384687 Merge branch 'pipelining' into parallel2 $ git merge ebc963d ... merge output ... $ git tag new-merge $ git reset --hard d415186 HEAD is now at d415186 Change parallel and parallel_ordered test parameters $ git checkout new-merge -- . $ echo ebc963d > .git/MERGE_HEAD $ git commit -m "Merge branch 'pipelining' into parallel2" [parallel2 92ca529] Merge branch 'pipelining' into parallel2 $ git tag forged-merge $ git reset --hard 34dca68 HEAD is now at 34dca68 Add ut-pipelining parallel_step $ git rebase 2384687 --onto forged-merge First, rewinding head to replay your work on top of it... Applying: Add TODO in parallel Applying: Strengthen parallel code, such that it does not require the number of items Applying: Add note about item_type in parallel.h Applying: Support step() in parallelized pipelines. Applying: Add ut-pipelining parallel_step $ git checkout pipelining Switched to branch 'pipelining' $ git merge --no-ff parallel2 Merge made by the 'recursive' strategy. ... merge output ...
Resultatet er følgende historik:
* 228a6bb (HEAD, pipelining) Merge branch 'parallel2' into pipelining |\ | * 9ba61db (parallel2) Add ut-pipelining parallel_step | * 12925e5 Support step() in parallelized pipelines. | * 6b1a139 Add note about item_type in parallel.h | * 6579195 Strengthen parallel code, such that it does not require the number of items | * d428d5b Add TODO in parallel | * c827808 (tag: forged-merge) Merge branch 'pipelining' into parallel2 | |\ | |/ |/| * | ebc963d (origin/pipelining) Gather pipelining documentation into a single document * | b0e0830 Simplify Graham scan code by using less templates * | 39c109c Use class keyword in pipelining when appropriate. * | 3f59291 fixup! Replace old convex hull app with new pipelining convex hull app * | c756184 Replace old convex hull app with new pipelining convex hull app * | 4422a60 Add iterators tests to CMakeLists * | f652286 Call pipe_segment::end() in actor order. * | 4b3f9c0 Use push_input_iterator in pipelining2 * | 016bf6f Add typed_push_output_iterators, for output iterators like ostream_iterator that define value_type to be void (why?) * | e888bc2 Make sorter forward number of items in output * | 6c60ab5 Fix memory overusage in pipelining * | 2fdaf91 Fix merge sorter crash when evacuating in internal reporting mode with no elements to sort * | 007776f Add ut-pipelining sorttrivial test to test sorting sequences of length 0, 1 and 2 | * d415186 Change parallel and parallel_ordered test parameters | * 9372b9c Add progress indicator to parallel test and change default modulus | * 2a1b9d4 More work on parallelism framework. | * a7b100c Fix ut-pipelining sequence generator/verifier | * e2b8a43 Add class-level documentation to parallel pipelining stuff | * 2055d48 Implement parallel pipelining processing as a library functionality |/ * dad266a Fix struct/class warning