Add a new class to write multi-thread safe to a complete directory

[soehms]

This new class is just a variation of the existing class atomic_write taking care of directory specific differences. For a first application case see #32099.

[soehms]

New commits:

​681cf4d

32344: initial version

[mkoeppe]

Haven't tried yet, but this part:

+            except OSError:
+                shutil.rmtree(self.target)
+                os.rename(self.tempname, self.target)

looks racy to me

[soehms]

Replying to mkoeppe:

Haven't tried yet, but this part:

+            except OSError:
+                shutil.rmtree(self.target)
+                os.rename(self.tempname, self.target)

looks racy to me

This code is just adapted from the corresponding part of atomic_write. It worked fine for me in all of my tests (using Python 3.9). But indeed, the second patchbot (using Python 3.7) shows (ignored) FileNotFoundError in cleanup:

Running doctests with ID 2021-08-08-00-50-13-492edc8c.
Git branch: patchbot/ticket_merged
Using --optional=build,ccache,debian,dochtml,pip,sage,sage_spkg
Doctesting entire Sage library.
Sorting sources by runtime so that slower doctests are run first....
Doctesting 4343 files using 5 threads.
....
sage -t --long --random-seed=0 src/doc/en/prep/Intro-Tutorial.rst
    [25 tests, 1.54 s]
Exception ignored in: <finalize object at 0x7fd572323bd0; dead>
Traceback (most recent call last):
  File "/usr/lib/python3.7/weakref.py", line 552, in __call__
    return info.func(*info.args, **(info.kwargs or {}))
  File "/usr/lib/python3.7/tempfile.py", line 934, in _cleanup
    _rmtree(name)
  File "/usr/lib/python3.7/shutil.py", line 482, in rmtree
    onerror(os.lstat, path, sys.exc_info())
  File "/usr/lib/python3.7/shutil.py", line 480, in rmtree
    orig_st = os.lstat(path)
FileNotFoundError: [Errno 2] No such file or directory: '/home/lelievre/.sage/temp/pascaline-sage-b/9091/tmp5ve0uefv'
Exception ignored in: <finalize object at 0x7fd572323bd0; dead>
Traceback (most recent call last):
  File "/usr/lib/python3.7/weakref.py", line 552, in __call__
    return info.func(*info.args, **(info.kwargs or {}))
  File "/usr/lib/python3.7/tempfile.py", line 934, in _cleanup
    _rmtree(name)
  File "/usr/lib/python3.7/shutil.py", line 482, in rmtree
    onerror(os.lstat, path, sys.exc_info())
  File "/usr/lib/python3.7/shutil.py", line 480, in rmtree
    orig_st = os.lstat(path)
FileNotFoundError: [Errno 2] No such file or directory: '/home/lelievre/.sage/temp/pascaline-sage-b/9091/tmpgp3b5u31'
Exception ignored in: <finalize object at 0x7fd572323bd0; dead>
Traceback (most recent call last):
  File "/usr/lib/python3.7/weakref.py", line 552, in __call__
    return info.func(*info.args, **(info.kwargs or {}))
  File "/usr/lib/python3.7/tempfile.py", line 934, in _cleanup
    _rmtree(name)
  File "/usr/lib/python3.7/shutil.py", line 482, in rmtree
    onerror(os.lstat, path, sys.exc_info())
  File "/usr/lib/python3.7/shutil.py", line 480, in rmtree
    orig_st = os.lstat(path)
FileNotFoundError: [Errno 2] No such file or directory: '/home/lelievre/.sage/temp/pascaline-sage-b/9091/tmpp9nuidju'
sage -t --long --random-seed=0 src/sage/misc/temporary_file.py
    [87 tests, 1.56 s]
....
----------------------------------------------------------------------
sage -t --long --random-seed=0 src/sage/symbolic/expression.pyx  # 1 doctest failed
----------------------------------------------------------------------
Total time for all tests: 2687.7 seconds
    cpu time: 12460.5 seconds
    cumulative wall time: 12941.0 seconds
Pytest is not installed, skip checking tests that rely on it.

Unfortunately, the traceback doesn't show how this is caused by my code. Do you have any ideas on how to make this part more safe?

[mkoeppe]

I think a first step should be to clarify the semantics in the documentation of this class: This is for creating a directory whose contents are determined uniquely by the directory name. If multiple threads or processes attempt to create it in parallel, then it does not matter which thread created it.

If this is the intended semantics, then the following should be correct:

            # Success: move temporary file to target file
            try:
                os.rename(self.tempname, self.target)
            except FileExistsError:
                # Race: Another thread or process must have created the directory
                pass

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​00b7106	Merge branch 'u/soehms/atomic_dir_32344' of git://trac.sagemath.org/sage into atomic_dir_32344
​6d4693d	32344: keep dir if it exists

[soehms]

Replying to mkoeppe:

I think a first step should be to clarify the semantics in the documentation of this class: This is for creating a directory whose contents are determined uniquely by the directory name. If multiple threads or processes attempt to create it in parallel, then it does not matter which thread created it.

If this is the intended semantics, then the following should be correct:

            # Success: move temporary file to target file
            try:
                os.rename(self.tempname, self.target)
            except FileExistsError
                # Race: Another thread or process must have created the directory
                pass

Good idea! If cleaning is necessary then the calling code is responsible. If so, it can still lead to a race of removing the directory but under better controlled conditions.

[mkoeppe]

LGTM

[soehms]

Many thanks!