output: #fixed code
                                  public void close(IotHubConnectionStatusChangeReason reason, Throwable cause) throws DeviceClientException
      {
          if (reason == null)
          {
              //Codes_SRS_IOTHUBTRANSPORT_34_026: [If the supplied reason is null, this function shall throw an
              // IllegalArgumentException.]
              throw new IllegalArgumentException("reason cannot be null");
          }
  
          this.cancelPendingPackets();
  
          //Codes_SRS_IOTHUBTRANSPORT_34_023: [This function shall invoke all callbacks.]
          this.invokeCallbacks();
  
          if (this.taskScheduler != null)
          {
              this.taskScheduler.shutdown();
          }
  
          if (this.scheduledExecutorService != null)
          {
              this.scheduledExecutorService.shutdownNow();
              this.scheduledExecutorService = null;
          }
  
          //Codes_SRS_IOTHUBTRANSPORT_34_024: [This function shall close the connection.]
          if (this.iotHubTransportConnection != null)
          {
              this.iotHubTransportConnection.close();
          }
  
          //Codes_SRS_IOTHUBTRANSPORT_34_025: [This function shall invoke updateStatus with status DISCONNECTED and the
          // supplied reason and cause.]
          this.updateStatus(IotHubConnectionStatus.DISCONNECTED, reason, cause);
  
          // Notify send thread to finish up so it doesn't survive this close
          synchronized (this.sendThreadLock)
          {
              this.sendThreadLock.notifyAll();
          }
  
          // Notify receive thread to finish up so it doesn't survive this close
          synchronized (this.receiveThreadLock)
          {
              this.receiveThreadLock.notifyAll();
          }
  
          log.info("Client connection closed successfully");
      }
input: #vulnerable code 
                                  public void close(IotHubConnectionStatusChangeReason reason, Throwable cause) throws DeviceClientException
      {
          if (reason == null)
          {
              //Codes_SRS_IOTHUBTRANSPORT_34_026: [If the supplied reason is null, this function shall throw an
              // IllegalArgumentException.]
              throw new IllegalArgumentException("reason cannot be null");
          }
  
          this.cancelPendingPackets();
  
          //Codes_SRS_IOTHUBTRANSPORT_34_023: [This function shall invoke all callbacks.]
          this.invokeCallbacks();
  
          if (this.taskScheduler != null)
          {
              this.taskScheduler.shutdown();
          }
  
          if (this.scheduledExecutorService != null)
          {
              this.scheduledExecutorService.shutdownNow();
              this.scheduledExecutorService = null;
          }
  
          //Codes_SRS_IOTHUBTRANSPORT_34_024: [This function shall close the connection.]
          if (this.iotHubTransportConnection != null)
          {
              this.iotHubTransportConnection.close();
          }
  
          //Codes_SRS_IOTHUBTRANSPORT_34_025: [This function shall invoke updateStatus with status DISCONNECTED and the
          // supplied reason and cause.]
          this.updateStatus(IotHubConnectionStatus.DISCONNECTED, reason, cause);
  
          log.info("Client connection closed successfully");
      } 
                              #location 23 
                              #vulnerability type THREAD_SAFETY_VIOLATION