[PATCH 5/5] [gdb/symtab] Fix data race on per_cu->lang

[Tom Tromey]

>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:

Tom> Both writes are called from the parallel for in dwarf2_build_psymtabs_hard,
Tom> this one directly:
Tom> ...
Tom>     #1 process_psymtab_comp_unit gdb/dwarf2/read.c:6812 (gdb+0x830912)
Tom>     #2 operator() gdb/dwarf2/read.c:7102 (gdb+0x831902)
Tom>     #3 operator() gdb/../gdbsupport/parallel-for.h:171 (gdb+0x8723a8)
Tom> ...
Tom> and this one when handling cross-CU refs:
Tom> ...
Tom>     #1 cooked_indexer::ensure_cu_exists(cutu_reader*, dwarf2_per_objfile*, \
Tom>     sect_offset, bool, bool) gdb/dwarf2/read.c:17973 (gdb+0x85c522)

This method tries to ensure that a CU isn't processed twice, using the
'scanned' field.  Do you know why this isn't working?

Tom> Fix this by guarding the write with a lock.

I would rather we avoid locks.  Ideally the existing exclusion mechanism
should be made to work, but if that fails, perhaps we can use another
atomic.

Tom