bvar: fix bad_weak_ptr crash in AgentCombiner::get_or_create_tls_agent

src/bvar/detail/combiner.h

@@ -341,7 +341,16 @@ friend class GlobalValue<self_type>;
         if (!agent->combiner.expired()) {
             return agent;
         }
-        agent->reset(_element_identity, this->shared_from_this());
+        self_shared_type self;
+        try {
+            self = this->shared_from_this();
+        } catch (const std::bad_weak_ptr&) {
+            // The combiner is no longer managed by any shared_ptr, which can
+            // happen when a bvar is being destroyed concurrently with a write.
+            // Silently skip this recording instead of crashing.
+            return NULL;
+        }
+        agent->reset(_element_identity, self);
         // TODO: Is uniqueness-checking necessary here?
         {
             butil::AutoLock guard(_lock);

src/bvar/detail/percentile.cpp

@@ -108,7 +108,6 @@ Percentile::value_type Percentile::get_value() const {
 Percentile &Percentile::operator<<(int64_t latency) {
     agent_type* agent = _combiner->get_or_create_tls_agent();
     if (BAIDU_UNLIKELY(!agent)) {
-        LOG(FATAL) << "Fail to create agent";
         return *this;
     }
     if (latency < 0) {

src/bvar/recorder.h

@@ -269,7 +269,6 @@ inline IntRecorder& IntRecorder::operator<<(int64_t sample) {
     }
     agent_type* agent = _combiner->get_or_create_tls_agent();
     if (BAIDU_UNLIKELY(!agent)) {
-        LOG(FATAL) << "Fail to create agent";
         return *this;
     }
     uint64_t n;

src/bvar/reducer.h

@@ -303,7 +303,6 @@ inline Reducer<T, Op, InvOp>& Reducer<T, Op, InvOp>::operator<<(
     // It's wait-free for most time
     agent_type* agent = _combiner->get_or_create_tls_agent();
     if (__builtin_expect(!agent, 0)) {
-        LOG(FATAL) << "Fail to create agent";
         return *this;
     }
     agent->element.modify(_combiner->op(), value);