Cannot identify image file

[magdasta]

https://github.com/golemfactory/golem/issues/3245

[magdasta]

For now we should log info if the file actually exists when this error occurs (to determine whether this is a problem with PIL or something really went wrong)

[Elfoniok]

This bug is caused because preview file is handled in two separate threads.

/golem/task/taskserver.py", line 140, in sync_network /golem/task/taskserver.py", line 881, in __remove_old_tasks /golem/task/taskmanager.py", line 787, in check_timeouts /golem/core/common.py", line 147, in func_wrapper /apps/rendering/task/framerenderingtask.py", line 131, in computation_failed /apps/rendering/task/framerenderingtask.py", line 338, in _update_frame_task_preview

and

/golem/network/transport/tcpnetwork.py", line 366, in _interpret
/golem/task/tasksession.py", line 123, in interpret /golem/network/transport/session.py", line 76, in interpret /golem/task/tasksession.py", line 485, in _react_to_want_to_compute_task /golem/task/taskmanager.py", line 396, in get_next_subtask /apps/blender/task/blenderrendertask.py", line 484, in query_extra_data /apps/rendering/task/framerenderingtask.py", line 338, in _update_frame_task_preview

Preview file can be corupted this way, and PIL yields that it can not identify image file.

In general removing tasks in Golem is very poorl handled because of python easier to ask for forgiveness than permission guidline, instead of ensuring that it is safe to delete task/subtask we just delete it and then handle lot of errors that it causes everywhere in datastructures of Golem.

We can go that way further and just provide proper locking of this file, or make it right this time.