BugFix: fix the issue of the client-side socket fd cannot be recycled…

… in a timely manner when using fiber connection pool, causing the number of close-wait to increase. (#108)

trpc/runtime/iomodel/reactor/fiber/fiber_connection.cc

@@ -352,6 +352,12 @@ void FiberConnection::QueueCleanupCallbackCheck() {
       read_mostly_.seldomly_used->error_events.load(std::memory_order_relaxed) == 0) {
     // Consider queue a call to `OnCleanup()` then.
     if (!read_mostly_.seldomly_used->cleanup_queued.exchange(true, std::memory_order_release)) {
+      {
+        std::scoped_lock<std::mutex> _(mutex_);
+        // Set the connection unavailability status flag in advance to make read/write tasks retreat in advance,
+        // reducing the conflict of Cleanup callback locks.
+        conn_unavailable_ = true;
+      }
       // No need to take a reference to us, `OnCleanup()` has not been called.
       GetReactor()->SubmitTask([this] {
         // The load below acts as a fence (paired with `exchange` above). (But

trpc/runtime/iomodel/reactor/fiber/fiber_connection.h

@@ -118,6 +118,12 @@ class alignas(hardware_destructive_interference_size) FiberConnection : public C
 
   std::atomic<std::size_t> restart_read_count_{0}, restart_write_count_{0};
 
+  // Connection closing cleanup and connection sending/receiving mutex lock, to protect connection cleanup and network
+  // data transmission/reception thread safety.
+  std::mutex mutex_;
+  // Connection unavailability status flag.
+  bool conn_unavailable_{false};
+
  private:
   void SuppressReadAndClearReadEvent();
   void SuppressAndClearWriteEvent();

trpc/runtime/iomodel/reactor/fiber/fiber_tcp_connection.cc

@@ -31,10 +31,6 @@ FiberTcpConnection::FiberTcpConnection(Reactor* reactor, const Socket& socket)
 }
 
 FiberTcpConnection::~FiberTcpConnection() {
-  // Requirements: destroy IO-handler before close socket.
-  GetIoHandler()->Destroy();
-  socket_.Close();
-
   TRPC_LOG_DEBUG("~FiberTcpConnection fd:" << socket_.GetFd() << ", conn_id:" << this->GetConnId());
   TRPC_ASSERT(!socket_.IsValid());
 }
@@ -116,7 +112,15 @@ int FiberTcpConnection::Send(IoMessage&& msg) {
     }
 
     constexpr auto kMaximumBytesPerCall = 1048576;
+    // External calls to the Send method may conflict with Socket closing concurrently, so a lock is added here for
+    // protection.
+    std::unique_lock<std::mutex> lock(mutex_);
+    // If the connection is unavailable, return an error directly.
+    if (conn_unavailable_) {
+      return -1;
+    }
     auto flush_status = FlushWritingBuffer(kMaximumBytesPerCall);
+    lock.unlock();
     if (TRPC_LIKELY(flush_status == FlushStatus::kFlushed)) {
       return 0;
     } else if (flush_status == FlushStatus::kSystemBufferSaturated || flush_status == FlushStatus::kQuotaExceeded) {
@@ -370,7 +374,13 @@ void FiberTcpConnection::OnCleanup(CleanupReason reason) {
 
   writing_buffers_.Stop();
 
-  // For multi-threads-safety, move "socket_.Close()" to ~FiberTcpConnection();
+  {
+    std::scoped_lock<std::mutex> _(mutex_);
+    conn_unavailable_ = true;
+    // Requirements: destroy IO-handler before close socket.
+    GetIoHandler()->Destroy();
+    socket_.Close();
+  }
 }
 
 IoHandler::HandshakeStatus FiberTcpConnection::DoHandshake(bool from_on_readable) {