Previously, priority was not randomly generated and was instead derived
from `GSequenceNode*` pointer value.
As a result, when a `GSequence` was freed and another was created, the
nodes were returned to memory allocator in such order that allocating
them again caused various performance problems in treap.
To my understanding, the problem develops like this :
1) Initially, memory allocator makes some nodes
2) For each node, priority is derived from pointer alone.
Due to the hash function, initially the priorities are reasonably
randomly distributed.
3) `GSequence` moves inserted nodes around to satisfy treap property.
The priority for node must be >= than priorities of its children
4) When `GSequence` is freed, it frees nodes in a new order.
It finds root node and then recursively frees left/right children.
Due to (3), hashes of freed nodes become partially ordered.
Note that this doesn't depend on choice of hash function.
5) Memory allocator will typically add freed chunks to free list.
This means that it will reallocate nodes in same or inverse order.
6) This results in order of hashes being more and more non-random.
7) This order happens to be increasingly anti-optimal.
That is, `GSequence` needs more `node_rotate` to maintain treap.
This also causes the tree to become more and more unbalanced.
The problem becomes worse with each iteration.
The solution is to use additional noise to maintain reasonable
randomness. This prevents "poisoning" the memory allocator.
On top of that, this patch somehow decreases average tree's height,
which is good because it speeds up various operations. I can't quite
explain why the height decreases with new code, probably the properties
of old hash function didn't quite match the needs of treap?
My averaged results for tree height with different sequence lengths:
Items | before| after |
--------+-------+---------------+
2 | 2,69 | 2,67 -00,74% |
4 | 3,71 | 3,80 +02,43% |
8 | 5,30 | 5,34 +00,75% |
16 | 7,45 | 7,22 -03,09% |
32 | 10,05 | 9,38 -06,67% |
64 | 12,97 | 11,72 -09,64% |
128 | 16,01 | 14,20 -11,31% |
256 | 19,11 | 16,77 -12,24% |
512 | 22,03 | 19,39 -11,98% |
1024 | 25,29 | 22,03 -12,89% |
2048 | 28,43 | 24,82 -12,70% |
4096 | 31,11 | 27,52 -11,54% |
8192 | 34,31 | 30,30 -11,69% |
16384 | 37,40 | 32,81 -12,27% |
32768 | 40,40 | 35,84 -11,29% |
65536 | 43,00 | 38,24 -11,07% |
131072 | 45,50 | 40,83 -10,26% |
262144 | 48,40 | 43,00 -11,16% |
524288 | 52,40 | 46,80 -10,69% |
The memory cost of the patch is zero on 64-bit, because the new field
uses the alignment hole between two other fields.
Note: priorities can sometimes have collisions. This is fine, because
treap allows equal priorities, but these will gradually decrease
performance. The hash function that was used previously has just one
collision on 0xbfff7fff in 32-bit space, but such pointer will not
occur because `g_slice_alloc()` always aligns to sizeof(void*).
However, in 64-bit space the old hash function had collisions anyway,
because it only uses lower 32 bits of pointer.
Closes#2468
Instead of calling xterm when it clearly does not exist and causes a silent error,
inform the user that the launch failed so they can take the right action.
Also added (transfer full) or (transfer none) annotations while I was at it.
This is the result of checking each `Returns:` line in these files. I’ve
only considered nullability and transferability, and not other (potentially
missing or incorrect) annotations.
Helps: #2227
If the first power-profile installed test fails (for example, because
xdg-desktop-portal isn’t available), correctly tear down the dbusmock
object, or it will cause setUp() to fail when the next test in the suite
is run.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #2481
When first creating the monitor, correctly set its property value to the
value from the portal, rather than waiting for the portal value to
change to set it.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: #2481
We were lucky that this worked in some cases (the test is racy), but we
should actually run the condition check each loop, rather than when the
function is called.
Spotted by Martin Pitt:
96a8c02d24 (r54773831)
The previous test was racy: it assumed that not all queued thread pool
jobs would start to be executed before `g_thread_pool_free()` was
called, whereas actually on some systems (particularly BSD ones), they
would all start (or even finish) being executed, and hence the free
function might never be called.
Rewrite the test to:
• Synchronise the test function and worker thread functions more
closely.
• Not bother about ordering the shared and exclusive variants of the
test differently. That seems to be a hangover from another test
above.
• Limit the number of worker threads to 1, rather than 2, since this
makes the test easier to control.
This has been tested with `--repeat 10000` on Linux, and it succeeds all
of those runs whereas previously it failed quite reliably.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Fixes: #2456
Now that `g_thread_pool_new_full()` can be used to set a user-provided
free function for queue elements, ensure that the internal dummy item
used to wake up the worker threads is removed from the queue before it’s
called.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #2456
This allows a pattern like
g_test_message ("cannot reticulate splines: %s", error->message);
g_test_fail ();
to be replaced by the simpler
g_test_fail_printf ("cannot reticulate splines: %s", error->message);
with the secondary benefit of making the message available to TAP
consumers as part of the "not ok" message.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Forming the g_test_skip() message from printf-style arguments seems
common enough to deserve a convenience function.
g_test_incomplete() is mechanically almost equivalent to g_test_skip()
(the semantics are different but the implementation is very similar),
so give it a similar mechanism for symmetry.
Signed-off-by: Simon McVittie <smcv@collabora.com>
