nasty memory leak in FAST_SEQ_UNSAFE macro

[sagetrac-dmharvey]

It appears that FAST_SEQ_UNSAFE creates a new reference to the list but never releases it.

It might be because PySequence_Fast returns a new reference, but PySequence_Fast_ITEMS doesn't release it.

See also

http://docs.python.org/api/sequence.html

CC: @sagetrac-dmharvey

Component: basic arithmetic

Issue created by migration from https://trac.sagemath.org/ticket/293

[robertwb]

comment:2

Replying to @williamstein:

Now that we have fast list indexing, there should be very few instances where we need to use this macro...

[williamstein]

comment:3

Confirmed. This is a major memory leak

[18:35] <william> indeed!
[18:35] <william> david harvey is totally right about that memory leak!
[18:35] <william> Try the following two distinct blocks of code, where m = get_memory_usage
[18:35] <william> print m()
[18:35] <william> n = random_matrix(RR, 200) 
[18:35] <william> n.set_immutable()
[18:35] <william> hash(n)
[18:35] <william> del n
[18:35] <william> m()
[18:35] <william>   -- and --
[18:35] <william> print m()
[18:35] <william> n = random_matrix(RR, 200) 
[18:35] <william> n.set_immutable()
[18:35] <william> del n
[18:35] <william> m()
[18:36] <william> The first leaks about 3MB every time.  The second doesn't leak at all.
[18:36] <robertwb> ouch
[18:36] <robertwb> yes, it's a new reference (though it may or may not be a new object)


print m()
n = random_matrix(RR, 200) 
n.set_immutable()
hash(n)
del n
m()

[robertwb]

Attachment: no-FAST_SEQ_UNSAFE.patch.gz

patch to remove all uses of FAST_SEQ_UNSAFE