3262a53c12
Unlinking a file may fail on Windows systems when the file is still held
open by another process. This is incompatible with POSIX semantics and
by extension with Git's assumed semantics when unlinking files, which
is that files can be unlinked regardless of whether they are still open
or not. To counteract this incompatibility, we have some custom error
handling in the `mingw_unlink()` wrapper that first retries the deletion
with some delay, and then asks the user whether we should continue to
retry.
While this logic might be sensible in many callsites throughout Git, it
is less when used in the reftable library. We only use unlink(3) there
to delete tables which aren't referenced anymore, and the code is very
aware of the limitations on Windows. As such, all calls to unlink(3p)
don't perform any error checking at all and are fine with the call
failing.
Instead, the library provides the `reftable_stack_clean()` function,
which Git knows to execute in git-pack-refs(1) after compacting a stack.
The effect of this function is that all stale tables will eventually get
deleted once they aren't kept open anymore.
So while we're fine with unlink(3p) failing, the Windows-emulation of
that function will still perform several sleeps and ultimately end up
asking the user:
$ git pack-refs
Unlink of file 'C:/temp/jgittest/jgit/.git/reftable/0x000000000002-0x000000000004-50486d0e.ref' failed. Should I try again? (y/n) n
Unlink of file 'C:/temp/jgittest/jgit/.git/reftable/0x000000000002-0x000000000004-50486d0e.ref' failed. Should I try again? (y/n) n
Unlink of file 'C:/temp/jgittest/jgit/.git/reftable/0x000000000002-0x000000000004-50486d0e.ref' failed. Should I try again? (y/n) n
It even asks multiple times, which is doubly annoying and puzzling to
the user:
1. It asks when trying to delete the old file after having written the
compacted stack.
2. It asks when reloading the stack, where it will try to unlink
now-unreferenced tables.
3. It asks when calling `reftable_stack_clean()`, where it will try to
unlink now-stale tables.
Fix the issue by making it possible to disable this behaviour with a
preprocessor define. As "git-compat-util.h" is only included from
"system.h", and given that "system.h" is only ever included by headers
and code that are internal to the reftable library, we can set that
macro in this header without impacting anything else but the reftable
library.
Reported-by: Christian Reich <Zottelbart@t-online.de>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
110 lines
3.4 KiB
C
110 lines
3.4 KiB
C
/*
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Copyright 2020 Google LLC
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Use of this source code is governed by a BSD-style
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license that can be found in the LICENSE file or at
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https://developers.google.com/open-source/licenses/bsd
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*/
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#ifndef SYSTEM_H
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#define SYSTEM_H
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/* This header glues the reftable library to the rest of Git */
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#define MINGW_DONT_HANDLE_IN_USE_ERROR
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#include "compat/posix.h"
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#include "compat/zlib-compat.h"
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/*
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* Return a random 32 bit integer. This function is expected to return
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* pre-seeded data.
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*/
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uint32_t reftable_rand(void);
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/*
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* An implementation-specific temporary file. By making this specific to the
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* implementation it becomes possible to tie temporary files into any kind of
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* signal or atexit handlers for cleanup on abnormal situations.
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*/
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struct reftable_tmpfile {
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const char *path;
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int fd;
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void *priv;
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};
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#define REFTABLE_TMPFILE_INIT ((struct reftable_tmpfile) { .fd = -1, })
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/*
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* Create a temporary file from a pattern similar to how mkstemp(3p) would.
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* The `pattern` shall not be modified. On success, the structure at `out` has
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* been initialized such that it is ready for use. Returns 0 on success, a
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* reftable error code on error.
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*/
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int tmpfile_from_pattern(struct reftable_tmpfile *out, const char *pattern);
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/*
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* Close the temporary file's file descriptor without removing the file itself.
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* This is a no-op in case the file has already been closed beforehand. Returns
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* 0 on success, a reftable error code on error.
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*/
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int tmpfile_close(struct reftable_tmpfile *t);
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/*
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* Close the temporary file and delete it. This is a no-op in case the file has
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* already been deleted or renamed beforehand. Returns 0 on success, a reftable
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* error code on error.
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*/
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int tmpfile_delete(struct reftable_tmpfile *t);
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/*
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* Rename the temporary file to the provided path. The temporary file must be
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* active. Return 0 on success, a reftable error code on error. Deactivates the
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* temporary file.
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*/
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int tmpfile_rename(struct reftable_tmpfile *t, const char *path);
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/*
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* An implementation-specific file lock. Same as with `reftable_tmpfile`,
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* making this specific to the implementation makes it possible to tie this
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* into signal or atexit handlers such that we know to clean up stale locks on
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* abnormal exits.
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*/
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struct reftable_flock {
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const char *path;
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int fd;
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void *priv;
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};
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#define REFTABLE_FLOCK_INIT ((struct reftable_flock){ .fd = -1, })
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/*
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* Acquire the lock for the given target path by exclusively creating a file
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* with ".lock" appended to it. If that lock exists, we wait up to `timeout_ms`
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* to acquire the lock. If `timeout_ms` is 0 we don't wait, if it is negative
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* we block indefinitely.
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*
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* Retrun 0 on success, a reftable error code on error.
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*/
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int flock_acquire(struct reftable_flock *l, const char *target_path,
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long timeout_ms);
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/*
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* Close the lockfile's file descriptor without removing the lock itself. This
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* is a no-op in case the lockfile has already been closed beforehand. Returns
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* 0 on success, a reftable error code on error.
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*/
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int flock_close(struct reftable_flock *l);
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/*
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* Release the lock by unlinking the lockfile. This is a no-op in case the
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* lockfile has already been released or committed beforehand. Returns 0 on
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* success, a reftable error code on error.
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*/
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int flock_release(struct reftable_flock *l);
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/*
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* Commit the lock by renaming the lockfile into place. Returns 0 on success, a
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* reftable error code on error.
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*/
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int flock_commit(struct reftable_flock *l);
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#endif
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