Kernels can be managed in two different modes. In XRT managed mode, kernel execution (starting/stopping/configuration) is managed by the underlying Xilinx Run Time (XRT). In this mode, the synchronization between different kernel instances executing simultaneously in different thread/process contexts is managed by XRT. This mode of operation is multi thread/multiprocess safe. XRT ensures that at any point, only one kernel context is given access to the actual kernel hardware resources.
The second mode of operation is user managed mode. In this mode, you are responsible to start, stop, and configure kernel using register read/write APIs. This mode is allowed only if the kernel object is created in exclusive mode. If the kernel is opened in exclusive mode, then only one instance of the kernel object can be created/opened.
It is strongly recommended to use a kernel in XRT managed mode by opening the kernel in shared mode as this is multi thread/multi-process safe and easy to configure.