Remove "while" loop for setting flags.

We only need the "while" loop if we are setting multiple flag bits
concurrently.  That's not needed, we only set RELEASED.  So, restructure
code, no while loop needed and someone can't accidently call the
function in the wrong way.

Author: nascheme

Objects/memoryobject.c

@@ -104,20 +104,24 @@ _PyManagedBuffer_FromObject(PyObject *base, int flags)
 }
 
 static inline int
-flags_test_and_set(int *flags, int bit)
+flags_set_released(int *flags, int released)
 {
 #ifdef Py_GIL_DISABLED
     int prev = _Py_atomic_load_int_relaxed(flags);
-    while (!_Py_atomic_compare_exchange_int(flags, &prev, prev | bit)) {
-        // Compare-exchange updates prev. Note that retries are bounded by the
-        // number of flag bits being concurrently set. So, yielding here is
-        // unnecessary.
+    if (prev & released) {
+        return 1;
     }
+    if (!_Py_atomic_compare_exchange_int(flags, &prev, prev | released)) {
+        // RELEASED is the only flag that can change concurrently.
+        assert(prev & released);
+        return 1;
+    }
+    return 0;
 #else
     int prev = *flags;
-    *flags = prev | bit;
+    *flags = prev | released;
+    return (prev & released) != 0;
 #endif
-    return (prev & bit) != 0;
 }
 
 static inline int
@@ -133,9 +137,9 @@ mv_has_flag(PyMemoryViewObject *mv, int bits)
 }
 
 static inline int
-mv_set_flag(PyMemoryViewObject *mv, int bit)
+mv_set_released(PyMemoryViewObject *mv)
 {
-    return flags_test_and_set(&mv->flags, bit);
+    return flags_set_released(&mv->flags, _Py_MEMORYVIEW_RELEASED);
 }
 
 static inline int
@@ -145,15 +149,15 @@ mbuf_has_flag(_PyManagedBufferObject *mbuf, int bits)
 }
 
 static inline int
-mbuf_set_flag(_PyManagedBufferObject *mbuf, int bit)
+mbuf_set_released(_PyManagedBufferObject *mbuf)
 {
-    return flags_test_and_set(&mbuf->flags, bit);
+    return flags_set_released(&mbuf->flags, _Py_MANAGED_BUFFER_RELEASED);
 }
 
 static void
 mbuf_release(_PyManagedBufferObject *self)
 {
-    if (mbuf_set_flag(self, _Py_MANAGED_BUFFER_RELEASED)) {
+    if (mbuf_set_released(self)) {
         return;
     }
 
@@ -1227,7 +1231,7 @@ static void
 _memory_release(PyMemoryViewObject *self)
 {
     assert(get_exports(self) == 0);
-    if (mv_set_flag(self, _Py_MEMORYVIEW_RELEASED)) {
+    if (mv_set_released(self)) {
         return;
     }