[GitHub] [celix] PengZheng commented on a change in pull request #399: Service tracker improvements

[GitBox]

PengZheng commented on a change in pull request #399:
URL: https://github.com/apache/celix/pull/399#discussion_r816548855



##########
File path: libs/framework/src/service_registration.c
##########
@@ -135,71 +131,71 @@ bool serviceRegistration_isValid(service_registration_pt 
registration) {
 
 celix_status_t serviceRegistration_unregister(service_registration_pt 
registration) {
        celix_status_t status = CELIX_SUCCESS;
-
-    bool notValidOrUnregistering;
-    celixThreadRwlock_readLock(&registration->lock);
-    notValidOrUnregistering = !serviceRegistration_isValid(registration) || 
registration->isUnregistering;
-    celixThreadRwlock_unlock(&registration->lock);
-
+    bool unregistering = false;
     registry_callback_t callback;
     callback.unregister = NULL;
-    bundle_pt bundle = NULL;
 
-       if (notValidOrUnregistering) {
-               status = CELIX_ILLEGAL_STATE;
-       } else {
-        celixThreadRwlock_writeLock(&registration->lock);
-        registration->isUnregistering = true;
-        bundle = registration->bundle;
-        callback = registration->callback;
-        celixThreadRwlock_unlock(&registration->lock);
+    // Without any further need of synchronization between callers, 
__ATOMIC_RELAXED should be sufficient to guarantee that only one caller has a 
chance to run.
+    // Strong form of compare-and-swap is used to avoid spurious failure.
+    if(!__atomic_compare_exchange_n(&registration->isUnregistering, 
&unregistering /* expected*/ , true /* desired */,
+                                    false /* weak */, 
__ATOMIC_RELAXED/*success memorder*/, __ATOMIC_RELAXED/*failure memorder*/)) {
+        status = CELIX_ILLEGAL_STATE;
+        goto immediate_return;

Review comment:
       Indeed, it's better to go without goto. Fixed.




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