lib/pthreadpool: protect jobs list from concurrent thread access

lib/pthreadpool: protect jobs list from concurrent thread access

ThreadSanitizer identifies a data race with pool->jobs with concurrent
threads in test added in previous commit.

This commit protects the pool->jobs list

(trace and line numbers are from before glue fix in previous commit)

WARNING: ThreadSanitizer: data race (pid=13574)
  Write of size 8 at 0x7b6000020260 by thread T16:
    #0 pthreadpool_tevent_job_done ../../lib/pthreadpool/pthreadpool_tevent.c:405 (pthreadpool_tevent_unit_test_san+0x407080)
    #1 tevent_common_invoke_immediate_handler ../../lib/tevent/tevent_immediate.c:190 (libtevent-private-samba.so+0x8dbf)
    #2 pthreadpool_tevent_job_fn ../../lib/pthreadpool/pthreadpool_tevent.c:351 (pthreadpool_tevent_unit_test_san+0x406bc4)
    #3 pthreadpool_server ../../lib/pthreadpool/pthreadpool.c:655 (pthreadpool_tevent_unit_test_san+0x4043bd)
    #4 <null> <null> (libtsan.so.0+0x323cf)

  Previous write of size 8 at 0x7b6000020260 by thread T13:
    #0 pthreadpool_tevent_job_send ../../lib/pthreadpool/pthreadpool_tevent.c:342 (pthreadpool_tevent_unit_test_san+0x406a09)
    #1 do_nested_pthread_job ../../lib/pthreadpool/test_pthreadpool_tevent.c:463 (pthreadpool_tevent_unit_test_san+0x408932)
    #2 pthreadpool_tevent_job_fn ../../lib/pthreadpool/pthreadpool_tevent.c:351 (pthreadpool_tevent_unit_test_san+0x406bc4)
    #3 pthreadpool_server ../../lib/pthreadpool/pthreadpool.c:655 (pthreadpool_tevent_unit_test_san+0x4043bd)
    #4 <null> <null> (libtsan.so.0+0x323cf)

  Thread T16 (tid=13591, running) created by main thread at:
    #0 pthread_create <null> (libtsan.so.0+0x5ed75)
    #1 pthreadpool_create_thread ../../lib/pthreadpool/pthreadpool.c:711 (pthreadpool_tevent_unit_test_san+0x4045ac)
    #2 pthreadpool_add_job ../../lib/pthreadpool/pthreadpool.c:792 (pthreadpool_tevent_unit_test_san+0x40496f)
    #3 pthreadpool_tevent_job_send ../../lib/pthreadpool/pthreadpool_tevent.c:329 (pthreadpool_tevent_unit_test_san+0x4065e2)
    #4 test_pthreadpool_tevent_job_send_multiple_3 ../../lib/pthreadpool/test_pthreadpool_tevent.c:515 (pthreadpool_tevent_unit_test_san+0x408c25)
    #5 cmocka_run_one_test_or_fixture ../../third_party/cmocka/cmocka.c:2948 (libcmocka-private-samba.so+0x6f92)
    #6 __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 (libc.so.6+0x40e6b)

  Thread T13 (tid=13588, running) created by main thread at:
    #0 pthread_create <null> (libtsan.so.0+0x5ed75)
    #1 pthreadpool_create_thread ../../lib/pthreadpool/pthreadpool.c:711 (pthreadpool_tevent_unit_test_san+0x4045ac)
    #2 pthreadpool_add_job ../../lib/pthreadpool/pthreadpool.c:792 (pthreadpool_tevent_unit_test_san+0x40496f)
    #3 pthreadpool_tevent_job_send ../../lib/pthreadpool/pthreadpool_tevent.c:329 (pthreadpool_tevent_unit_test_san+0x4065e2)
    #4 test_pthreadpool_tevent_job_send_multiple_3 ../../lib/pthreadpool/test_pthreadpool_tevent.c:515 (pthreadpool_tevent_unit_test_san+0x408c25)
    #5 cmocka_run_one_test_or_fixture ../../third_party/cmocka/cmocka.c:2948 (libcmocka-private-samba.so+0x6f92)
    #6 __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 (libc.so.6+0x40e6b)

SUMMARY: ThreadSanitizer: data race ../../lib/pthreadpool/pthreadpool_tevent.c:405 in pthreadpool_tevent_job_done

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15958
Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Sun Jan 18 15:16:59 UTC 2026 on atb-devel-224