clCreateContext returns a valid non-zero context and errcode_ret is set to CL_SUCCESS if the context is created successfully. Otherwise, it returns NULL value with the following error values returned in errcode_ret:
* CL_INVALID_VALUE if context property name in properties is not a supported property name; if devices is NULL; if num_devices is equal to zero; or if pfn_notify is NULL but user_data is not NULL.