git/epoch.c
Jon Seymour 99c2bc9300 [PATCH] Fix for git-rev-list --merge-order B ^A (A,B share common base) [rev 2]
This patch makes --merge-order produce the same list as git-rev-list
without --merge-order specified.

In particular, if the graph looks like this:

A
| B
|/
C
|
D

The both git-rev-list B ^A and git-rev-list --merge-order will produce B.

The unit tests have been changed to reflect the fact that the prune
points are now formally part of the start list that is used to perform
the --merge-order sort.

That is: git-rev-list --merge-order A ^D used to produce

= A
| C

It now produces:

^ A
| C

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-29 20:53:10 -07:00

646 lines
17 KiB
C

/*
* Copyright (c) 2005, Jon Seymour
*
* For more information about epoch theory on which this module is based,
* refer to http://blackcubes.dyndns.org/epoch/. That web page defines
* terms such as "epoch" and "minimal, non-linear epoch" and provides rationales
* for some of the algorithms used here.
*
*/
#include <stdlib.h>
/* Provides arbitrary precision integers required to accurately represent
* fractional mass: */
#include <openssl/bn.h>
#include "cache.h"
#include "commit.h"
#include "epoch.h"
struct fraction {
BIGNUM numerator;
BIGNUM denominator;
};
#define HAS_EXACTLY_ONE_PARENT(n) ((n)->parents && !(n)->parents->next)
static BN_CTX *context = NULL;
static struct fraction *one = NULL;
static struct fraction *zero = NULL;
static BN_CTX *get_BN_CTX()
{
if (!context) {
context = BN_CTX_new();
}
return context;
}
static struct fraction *new_zero()
{
struct fraction *result = xmalloc(sizeof(*result));
BN_init(&result->numerator);
BN_init(&result->denominator);
BN_zero(&result->numerator);
BN_one(&result->denominator);
return result;
}
static void clear_fraction(struct fraction *fraction)
{
BN_clear(&fraction->numerator);
BN_clear(&fraction->denominator);
}
static struct fraction *divide(struct fraction *result, struct fraction *fraction, int divisor)
{
BIGNUM bn_divisor;
BN_init(&bn_divisor);
BN_set_word(&bn_divisor, divisor);
BN_copy(&result->numerator, &fraction->numerator);
BN_mul(&result->denominator, &fraction->denominator, &bn_divisor, get_BN_CTX());
BN_clear(&bn_divisor);
return result;
}
static struct fraction *init_fraction(struct fraction *fraction)
{
BN_init(&fraction->numerator);
BN_init(&fraction->denominator);
BN_zero(&fraction->numerator);
BN_one(&fraction->denominator);
return fraction;
}
static struct fraction *get_one()
{
if (!one) {
one = new_zero();
BN_one(&one->numerator);
}
return one;
}
static struct fraction *get_zero()
{
if (!zero) {
zero = new_zero();
}
return zero;
}
static struct fraction *copy(struct fraction *to, struct fraction *from)
{
BN_copy(&to->numerator, &from->numerator);
BN_copy(&to->denominator, &from->denominator);
return to;
}
static struct fraction *add(struct fraction *result, struct fraction *left, struct fraction *right)
{
BIGNUM a, b, gcd;
BN_init(&a);
BN_init(&b);
BN_init(&gcd);
BN_mul(&a, &left->numerator, &right->denominator, get_BN_CTX());
BN_mul(&b, &left->denominator, &right->numerator, get_BN_CTX());
BN_mul(&result->denominator, &left->denominator, &right->denominator, get_BN_CTX());
BN_add(&result->numerator, &a, &b);
BN_gcd(&gcd, &result->denominator, &result->numerator, get_BN_CTX());
BN_div(&result->denominator, NULL, &result->denominator, &gcd, get_BN_CTX());
BN_div(&result->numerator, NULL, &result->numerator, &gcd, get_BN_CTX());
BN_clear(&a);
BN_clear(&b);
BN_clear(&gcd);
return result;
}
static int compare(struct fraction *left, struct fraction *right)
{
BIGNUM a, b;
int result;
BN_init(&a);
BN_init(&b);
BN_mul(&a, &left->numerator, &right->denominator, get_BN_CTX());
BN_mul(&b, &left->denominator, &right->numerator, get_BN_CTX());
result = BN_cmp(&a, &b);
BN_clear(&a);
BN_clear(&b);
return result;
}
struct mass_counter {
struct fraction seen;
struct fraction pending;
};
static struct mass_counter *new_mass_counter(struct commit *commit, struct fraction *pending)
{
struct mass_counter *mass_counter = xmalloc(sizeof(*mass_counter));
memset(mass_counter, 0, sizeof(*mass_counter));
init_fraction(&mass_counter->seen);
init_fraction(&mass_counter->pending);
copy(&mass_counter->pending, pending);
copy(&mass_counter->seen, get_zero());
if (commit->object.util) {
die("multiple attempts to initialize mass counter for %s",
sha1_to_hex(commit->object.sha1));
}
commit->object.util = mass_counter;
return mass_counter;
}
static void free_mass_counter(struct mass_counter *counter)
{
clear_fraction(&counter->seen);
clear_fraction(&counter->pending);
free(counter);
}
/*
* Finds the base commit of a list of commits.
*
* One property of the commit being searched for is that every commit reachable
* from the base commit is reachable from the commits in the starting list only
* via paths that include the base commit.
*
* This algorithm uses a conservation of mass approach to find the base commit.
*
* We start by injecting one unit of mass into the graph at each
* of the commits in the starting list. Injecting mass into a commit
* is achieved by adding to its pending mass counter and, if it is not already
* enqueued, enqueuing the commit in a list of pending commits, in latest
* commit date first order.
*
* The algorithm then preceeds to visit each commit in the pending queue.
* Upon each visit, the pending mass is added to the mass already seen for that
* commit and then divided into N equal portions, where N is the number of
* parents of the commit being visited. The divided portions are then injected
* into each of the parents.
*
* The algorithm continues until we discover a commit which has seen all the
* mass originally injected or until we run out of things to do.
*
* If we find a commit that has seen all the original mass, we have found
* the common base of all the commits in the starting list.
*
* The algorithm does _not_ depend on accurate timestamps for correct operation.
* However, reasonably sane (e.g. non-random) timestamps are required in order
* to prevent an exponential performance characteristic. The occasional
* timestamp inaccuracy will not dramatically affect performance but may
* result in more nodes being processed than strictly necessary.
*
* This procedure sets *boundary to the address of the base commit. It returns
* non-zero if, and only if, there was a problem parsing one of the
* commits discovered during the traversal.
*/
static int find_base_for_list(struct commit_list *list, struct commit **boundary)
{
int ret = 0;
struct commit_list *cleaner = NULL;
struct commit_list *pending = NULL;
struct fraction injected;
init_fraction(&injected);
*boundary = NULL;
for (; list; list = list->next) {
struct commit *item = list->item;
if (!item->object.util) {
new_mass_counter(list->item, get_one());
add(&injected, &injected, get_one());
commit_list_insert(list->item, &cleaner);
commit_list_insert(list->item, &pending);
}
}
while (!*boundary && pending && !ret) {
struct commit *latest = pop_commit(&pending);
struct mass_counter *latest_node = (struct mass_counter *) latest->object.util;
int num_parents;
if ((ret = parse_commit(latest)))
continue;
add(&latest_node->seen, &latest_node->seen, &latest_node->pending);
num_parents = count_parents(latest);
if (num_parents) {
struct fraction distribution;
struct commit_list *parents;
divide(init_fraction(&distribution), &latest_node->pending, num_parents);
for (parents = latest->parents; parents; parents = parents->next) {
struct commit *parent = parents->item;
struct mass_counter *parent_node = (struct mass_counter *) parent->object.util;
if (!parent_node) {
parent_node = new_mass_counter(parent, &distribution);
insert_by_date(&pending, parent);
commit_list_insert(parent, &cleaner);
} else {
if (!compare(&parent_node->pending, get_zero()))
insert_by_date(&pending, parent);
add(&parent_node->pending, &parent_node->pending, &distribution);
}
}
clear_fraction(&distribution);
}
if (!compare(&latest_node->seen, &injected))
*boundary = latest;
copy(&latest_node->pending, get_zero());
}
while (cleaner) {
struct commit *next = pop_commit(&cleaner);
free_mass_counter((struct mass_counter *) next->object.util);
next->object.util = NULL;
}
if (pending)
free_commit_list(pending);
clear_fraction(&injected);
return ret;
}
/*
* Finds the base of an minimal, non-linear epoch, headed at head, by
* applying the find_base_for_list to a list consisting of the parents
*/
static int find_base(struct commit *head, struct commit **boundary)
{
int ret = 0;
struct commit_list *pending = NULL;
struct commit_list *next;
for (next = head->parents; next; next = next->next) {
commit_list_insert(next->item, &pending);
}
ret = find_base_for_list(pending, boundary);
free_commit_list(pending);
return ret;
}
/*
* This procedure traverses to the boundary of the first epoch in the epoch
* sequence of the epoch headed at head_of_epoch. This is either the end of
* the maximal linear epoch or the base of a minimal non-linear epoch.
*
* The queue of pending nodes is sorted in reverse date order and each node
* is currently in the queue at most once.
*/
static int find_next_epoch_boundary(struct commit *head_of_epoch, struct commit **boundary)
{
int ret;
struct commit *item = head_of_epoch;
ret = parse_commit(item);
if (ret)
return ret;
if (HAS_EXACTLY_ONE_PARENT(item)) {
/*
* We are at the start of a maximimal linear epoch.
* Traverse to the end.
*/
while (HAS_EXACTLY_ONE_PARENT(item) && !ret) {
item = item->parents->item;
ret = parse_commit(item);
}
*boundary = item;
} else {
/*
* Otherwise, we are at the start of a minimal, non-linear
* epoch - find the common base of all parents.
*/
ret = find_base(item, boundary);
}
return ret;
}
/*
* Returns non-zero if parent is known to be a parent of child.
*/
static int is_parent_of(struct commit *parent, struct commit *child)
{
struct commit_list *parents;
for (parents = child->parents; parents; parents = parents->next) {
if (!memcmp(parent->object.sha1, parents->item->object.sha1,
sizeof(parents->item->object.sha1)))
return 1;
}
return 0;
}
/*
* Pushes an item onto the merge order stack. If the top of the stack is
* marked as being a possible "break", we check to see whether it actually
* is a break.
*/
static void push_onto_merge_order_stack(struct commit_list **stack, struct commit *item)
{
struct commit_list *top = *stack;
if (top && (top->item->object.flags & DISCONTINUITY)) {
if (is_parent_of(top->item, item)) {
top->item->object.flags &= ~DISCONTINUITY;
}
}
commit_list_insert(item, stack);
}
/*
* Marks all interesting, visited commits reachable from this commit
* as uninteresting. We stop recursing when we reach the epoch boundary,
* an unvisited node or a node that has already been marking uninteresting.
*
* This doesn't actually mark all ancestors between the start node and the
* epoch boundary uninteresting, but does ensure that they will eventually
* be marked uninteresting when the main sort_first_epoch() traversal
* eventually reaches them.
*/
static void mark_ancestors_uninteresting(struct commit *commit)
{
unsigned int flags = commit->object.flags;
int visited = flags & VISITED;
int boundary = flags & BOUNDARY;
int uninteresting = flags & UNINTERESTING;
struct commit_list *next;
commit->object.flags |= UNINTERESTING;
/*
* We only need to recurse if
* we are not on the boundary and
* we have not already been marked uninteresting and
* we have already been visited.
*
* The main sort_first_epoch traverse will mark unreachable
* all uninteresting, unvisited parents as they are visited
* so there is no need to duplicate that traversal here.
*
* Similarly, if we are already marked uninteresting
* then either all ancestors have already been marked
* uninteresting or will be once the sort_first_epoch
* traverse reaches them.
*/
if (uninteresting || boundary || !visited)
return;
for (next = commit->parents; next; next = next->next)
mark_ancestors_uninteresting(next->item);
}
/*
* Sorts the nodes of the first epoch of the epoch sequence of the epoch headed at head
* into merge order.
*/
static void sort_first_epoch(struct commit *head, struct commit_list **stack)
{
struct commit_list *parents;
head->object.flags |= VISITED;
/*
* TODO: By sorting the parents in a different order, we can alter the
* merge order to show contemporaneous changes in parallel branches
* occurring after "local" changes. This is useful for a developer
* when a developer wants to see all changes that were incorporated
* into the same merge as her own changes occur after her own
* changes.
*/
for (parents = head->parents; parents; parents = parents->next) {
struct commit *parent = parents->item;
if (head->object.flags & UNINTERESTING) {
/*
* Propagates the uninteresting bit to all parents.
* if we have already visited this parent, then
* the uninteresting bit will be propagated to each
* reachable commit that is still not marked
* uninteresting and won't otherwise be reached.
*/
mark_ancestors_uninteresting(parent);
}
if (!(parent->object.flags & VISITED)) {
if (parent->object.flags & BOUNDARY) {
if (*stack) {
die("something else is on the stack - %s",
sha1_to_hex((*stack)->item->object.sha1));
}
push_onto_merge_order_stack(stack, parent);
parent->object.flags |= VISITED;
} else {
sort_first_epoch(parent, stack);
if (parents) {
/*
* This indicates a possible
* discontinuity it may not be be
* actual discontinuity if the head
* of parent N happens to be the tail
* of parent N+1.
*
* The next push onto the stack will
* resolve the question.
*/
(*stack)->item->object.flags |= DISCONTINUITY;
}
}
}
}
push_onto_merge_order_stack(stack, head);
}
/*
* Emit the contents of the stack.
*
* The stack is freed and replaced by NULL.
*
* Sets the return value to STOP if no further output should be generated.
*/
static int emit_stack(struct commit_list **stack, emitter_func emitter, int include_last)
{
unsigned int seen = 0;
int action = CONTINUE;
while (*stack && (action != STOP)) {
struct commit *next = pop_commit(stack);
seen |= next->object.flags;
if (*stack || include_last) {
if (!*stack)
next->object.flags |= BOUNDARY;
action = (*emitter) (next);
}
}
if (*stack) {
free_commit_list(*stack);
*stack = NULL;
}
return (action == STOP || (seen & UNINTERESTING)) ? STOP : CONTINUE;
}
/*
* Sorts an arbitrary epoch into merge order by sorting each epoch
* of its epoch sequence into order.
*
* Note: this algorithm currently leaves traces of its execution in the
* object flags of nodes it discovers. This should probably be fixed.
*/
static int sort_in_merge_order(struct commit *head_of_epoch, emitter_func emitter)
{
struct commit *next = head_of_epoch;
int ret = 0;
int action = CONTINUE;
ret = parse_commit(head_of_epoch);
next->object.flags |= BOUNDARY;
while (next && next->parents && !ret && (action != STOP)) {
struct commit *base = NULL;
ret = find_next_epoch_boundary(next, &base);
if (ret)
return ret;
next->object.flags |= BOUNDARY;
if (base)
base->object.flags |= BOUNDARY;
if (HAS_EXACTLY_ONE_PARENT(next)) {
while (HAS_EXACTLY_ONE_PARENT(next)
&& (action != STOP)
&& !ret) {
if (next->object.flags & UNINTERESTING) {
action = STOP;
} else {
action = (*emitter) (next);
}
if (action != STOP) {
next = next->parents->item;
ret = parse_commit(next);
}
}
} else {
struct commit_list *stack = NULL;
sort_first_epoch(next, &stack);
action = emit_stack(&stack, emitter, (base == NULL));
next = base;
}
}
if (next && (action != STOP) && !ret) {
(*emitter) (next);
}
return ret;
}
/*
* Sorts the nodes reachable from a starting list in merge order, we
* first find the base for the starting list and then sort all nodes
* in this subgraph using the sort_first_epoch algorithm. Once we have
* reached the base we can continue sorting using sort_in_merge_order.
*/
int sort_list_in_merge_order(struct commit_list *list, emitter_func emitter)
{
struct commit_list *stack = NULL;
struct commit *base;
int ret = 0;
int action = CONTINUE;
struct commit_list *reversed = NULL;
for (; list; list = list->next) {
struct commit *next = list->item;
if (!(next->object.flags & DUPCHECK)) {
next->object.flags |= DUPCHECK;
commit_list_insert(list->item, &reversed);
}
}
if (!reversed)
return ret;
else if (!reversed->next) {
/*
* If there is only one element in the list, we can sort it
* using sort_in_merge_order.
*/
base = reversed->item;
} else {
/*
* Otherwise, we search for the base of the list.
*/
ret = find_base_for_list(reversed, &base);
if (ret)
return ret;
if (base)
base->object.flags |= BOUNDARY;
while (reversed) {
struct commit * next = pop_commit(&reversed);
if (!(next->object.flags & VISITED)) {
sort_first_epoch(next, &stack);
if (reversed) {
/*
* If we have more commits
* to push, then the first
* push for the next parent may
* (or may * not) represent a
* discontinuity with respect
* to the parent currently on
* the top of the stack.
*
* Mark it for checking here,
* and check it with the next
* push. See sort_first_epoch()
* for more details.
*/
stack->item->object.flags |= DISCONTINUITY;
}
}
}
action = emit_stack(&stack, emitter, (base==NULL));
}
if (base && (action != STOP)) {
ret = sort_in_merge_order(base, emitter);
}
return ret;
}