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-rw-r--r--libguile/atomic.c19
-rw-r--r--libguile/intrinsics.c18
2 files changed, 30 insertions, 7 deletions
diff --git a/libguile/atomic.c b/libguile/atomic.c
index 604a21e5a..174d26b76 100644
--- a/libguile/atomic.c
+++ b/libguile/atomic.c
@@ -1,4 +1,4 @@
-/* Copyright 2016,2018
+/* Copyright 2016,2018-2019
Free Software Foundation, Inc.
This file is part of Guile.
@@ -102,10 +102,21 @@ SCM_DEFINE (scm_atomic_box_compare_and_swap_x,
"if the return value is @code{eq?} to @var{expected}.")
#define FUNC_NAME s_scm_atomic_box_compare_and_swap_x
{
+ SCM result = expected;
+
SCM_VALIDATE_ATOMIC_BOX (1, box);
- scm_atomic_compare_and_swap_scm (scm_atomic_box_loc (box),
- &expected, desired);
- return expected;
+ while (!scm_atomic_compare_and_swap_scm (scm_atomic_box_loc (box),
+ &result, desired)
+ && scm_is_eq (result, 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. */
+ }
+ return result;
}
#undef FUNC_NAME
diff --git a/libguile/intrinsics.c b/libguile/intrinsics.c
index a619fda90..437441032 100644
--- a/libguile/intrinsics.c
+++ b/libguile/intrinsics.c
@@ -1,4 +1,4 @@
-/* Copyright 2018
+/* Copyright 2018-2019
Free Software Foundation, Inc.
This file is part of Guile.
@@ -459,8 +459,20 @@ atomic_swap_scm (SCM *loc, SCM val)
static SCM
atomic_compare_and_swap_scm (SCM *loc, SCM expected, SCM desired)
{
- scm_atomic_compare_and_swap_scm (loc, &expected, desired);
- return expected;
+ SCM result = expected;
+
+ while (!scm_atomic_compare_and_swap_scm (loc, &result, desired)
+ && scm_is_eq (result, 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. */
+ }
+
+ return result;
}
void