Asammdf keeps file open when it cannot read it correctly

[eblis]

Python version

Asammdf 7.4.2 Python 3.9 and 3.11

Code

MDF version

4.10

Code snippet

try:
  with MDF(file_path) as mdf_obj:
    # ..
except Exception as ex:
  # mdf_obj.close() # can't call this function as mdf_obj is not defined anymore, and was never assigned a value to begin with
  move_file(file_path, "some/other/folder") # permission error, file_path is still in use

Traceback

I don't have a traceback as I debugged this issue on a colleague's machine, but I can show you the call trail.

Description

Asammdf keeps a file open after it has finished attempting to read from it (and failed with an exception), and we cannot access the file to move it even after asammdf object is out of scope. And since the asammdf object is out of scope we cannot manually try to close the file with mdf_obj.close() as mdf_obj isn't defined anymore.

We have an MDF file with 4.10 version, around 2GB in size which throws an exception in MDF.init() which has 2 issues:

1. The with statement cannot be used for such files, as it never enters the context manager, since the __init__() function crashes before __enter__ has a chance to be called. Since __enter__ is never called, nor will __exit__ be called so there's no way for MDF object to close itself automatically.
2. The bigger issue I think, the underlying file is kept open by asammdf even after __init__ has crashed with an exception, preventing anyone else from opening the file for writing or from moving the file to another location.

the with MDF(file_path) as mdf_obj: statement calls are like this:

• first MDF.__init__() is called, here
• Since this is version 4.10 we end up loading MDF4
• So MDF4.__init__() is called, here
• After some initializations and some other things, it memory maps the file and tries to read it, here
• First part is read ok, but when we get to read the HeaderBlock it crashes with some kind of seek offset error,
• At this point an exception is raised and the with statement never finishes executing (context manager never engages). If we didn't have the try/catch block it would raise the exception to the calling method
• Since __enter__ was never called, nor will __exit__ be called, so the MDF file has opened file_path and never closed it at this point.
• And the bigger problem, the call to move_file(file_path, "some/other/folder") fails with permission error as the file_path is still kept open by mdf_obj, even though mdf_obj is no longer defined and cannot be used in code.

[danielhrisca]

@eblis please try the development branch code

[eblis]

The move operation is still prevented with permission error. I think you need to close more than just the file.

We tried with the following changes and then it started working. Is there any downside to closing everything, calling close() on the MDF object, not only the _file ?

-                except:
-                    if self._file:
-                        self._file.close()
-                    raise
+                except:
+                    self.close()
+                    raise

[danielhrisca]

new commit

[eblis]

This works