gpgscm: Avoid cell allocation overhead.
authorJustus Winter <justus@g10code.com>
Mon, 14 Nov 2016 11:37:36 +0000 (12:37 +0100)
committerJustus Winter <justus@g10code.com>
Mon, 14 Nov 2016 15:11:15 +0000 (16:11 +0100)
commit83c184a66b73f312425b01008f0495610e5329a4
tree4443a9636aedb4fb9338fa5b79fe82bc6a183e72
parent4ee4d0b02172cf56d9582bb99e32a65c75315b25
gpgscm: Avoid cell allocation overhead.

* tests/gpgscm/scheme-private.h (struct scheme): New fields
'inhibit_gc', 'reserved_cells', and 'reserved_lineno'.
* tests/gpgscm/scheme.c (GC_ENABLED): New macro.
(USE_GC_LOCKING): Likewise.
(gc_reservations): Likewise.
(gc_reservation_failure): New function.
(_gc_disable): Likewise.
(gc_disable): New macro.
(gc_enable): Likewise.
(gc_enabled): Likewise.
(gc_consume): Likewise.
(get_cell_x): Consume reserved cell if garbage collection is disabled.
(_get_cell): Assert that gc is enabled.
(get_cell): Only record cell in the list of recently allocated cells
if gc is enabled.
(get_vector_object): Likewise.
(gc): Assert that gc is enabled.
(s_return): Add comment, adjust call to '_s_return'.
(s_return_enable_gc): New macro.
(_s_return): Add flag 'enable_gc' and re-enable gc if set.
(oblist_add_by_name): Use the new facilities to protect the
allocations.
(new_frame_in_env): Likewise.
(new_slot_spec_in_env): Likewise.
(s_save): Likewise.
(opexe_0): Likewise.
(opexe_1): Likewise.
(opexe_2): Likewise.
(opexe_5): Likewise.
(opexe_6): Likewise.
(scheme_init_custom_alloc): Initialize the new fields.
--

Every time a cell is allocated, the interpreter may run out of free
cells and do a garbage collection.  This is problematic because it
might garbage collect objects that have been allocated, but are not
yet made available to the interpreter.

Previously, we would plug such newly allocated cells into the list of
newly allocated objects rooted at car(sc->sink), but that requires
allocating yet another cell increasing pressure on the memory
management system.

A faster alternative is to preallocate the cells needed for an
operation and make sure the garbage collection is not run until all
allocated objects are plugged in.  This can be done with gc_disable
and gc_enable.

This optimization can be applied incrementally.  This commit picks all
low-hanging fruits.

Signed-off-by: Justus Winter <justus@g10code.com>
tests/gpgscm/scheme-private.h
tests/gpgscm/scheme.c