diff options
Diffstat (limited to 'libguile/vm-engine.c')
| -rw-r--r-- | libguile/vm-engine.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/libguile/vm-engine.c b/libguile/vm-engine.c index 19ff3e498..53d7f3522 100644 --- a/libguile/vm-engine.c +++ b/libguile/vm-engine.c @@ -3868,16 +3868,25 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp, { scm_t_uint16 dst, box; scm_t_uint32 expected, desired; - SCM scm_box, scm_expected; + SCM scm_box, scm_expected, scm_result; UNPACK_12_12 (op, dst, box); UNPACK_24 (ip[1], expected); UNPACK_24 (ip[2], desired); scm_box = SP_REF (box); VM_VALIDATE_ATOMIC_BOX (scm_box, "atomic-box-compare-and-swap!"); - scm_expected = SP_REF (expected); - scm_atomic_compare_and_swap_scm (scm_atomic_box_loc (scm_box), - &scm_expected, SP_REF (desired)); - SP_SET (dst, scm_expected); + scm_result = scm_expected = SP_REF (expected); + while (!scm_atomic_compare_and_swap_scm (scm_atomic_box_loc (scm_box), + &scm_result, SP_REF (desired)) + && scm_is_eq (scm_result, scm_expected)) + { + /* 'scm_atomic_compare_and_swap_scm' has spuriously failed, + i.e. it has returned 0 to indicate failure, although the + observed value is 'eq?' to EXPECTED. In this case, we *must* + try again, because the API of 'atomic-box-compare-and-swap!' + provides no way to indicate to the caller that the exchange + failed when the observed value is 'eq?' to EXPECTED. */ + } + SP_SET (dst, scm_result); NEXT (3); } |