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Ævar Arnfjörð Bjarmason 88ce3ef636 *.[ch] refactoring: make use of the FREE_AND_NULL() macro
Replace occurrences of `free(ptr); ptr = NULL` which weren't caught by
the coccinelle rule. These fall into two categories:

 - free/NULL assignments one after the other which coccinelle all put
   on one line, which is functionally equivalent code, but very ugly.

 - manually spotted occurrences where the NULL assignment isn't right
   after the free() call.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-06-16 12:44:09 -07:00
Junio C Hamano b0f89870ea Merge branch 'jk/prio-queue-avoid-swap-with-self'
Code clean-up.

* jk/prio-queue-avoid-swap-with-self:
  prio_queue_reverse: don't swap elements with themselves
2017-05-01 14:14:43 +09:00
Jeff King 1f9e18b772 prio_queue_reverse: don't swap elements with themselves
Our array-reverse algorithm does the usual "walk from both
ends, swapping elements". We can quit when the two indices
are equal, since:

  1. Swapping an element with itself is a noop.

  2. If i and j are equal, then in the next iteration i is
     guaranteed to be bigge than j, and we will exit the
     loop.

So exiting the loop on equality is slightly more efficient.
And more importantly, the new SWAP() macro does not expect
to handle noop swaps; it will call memcpy() with the same src
and dst pointers in this case. It's unclear whether that
causes a problem on any platforms by violating the
"overlapping memory" constraint of memcpy, but it does cause
valgrind to complain.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-04-24 21:16:44 -07:00
René Scharfe 35d803bc9a use SWAP macro
Apply the semantic patch swap.cocci to convert hand-rolled swaps to use
the macro SWAP.  The resulting code is shorter and easier to read, the
object code is effectively unchanged.

The patch for object.c had to be hand-edited in order to preserve the
comment before the change; Coccinelle tried to eat it for some reason.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-01-30 14:17:00 -08:00
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>
2014-07-15 11:02:54 -07:00
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>
2014-07-15 11:02:53 -07:00
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>
2013-06-11 15:15:21 -07:00
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>
2013-06-11 15:15:21 -07:00