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diff mercurial/scmutil.py @ 29999:57830bd0e787

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scmutil: add file object wrapper class to check ambiguity at closing In Mercurial source tree, opening a file in "a"/"a+" mode like below doesn't specify atomictemp=True for vfs, and this avoids file stat ambiguity check by atomictempfile. - writing changes out in revlog layer uses "a+" mode - truncation in repair.strip() uses "a" mode - truncation in transaction._playback() uses "a" mode If steps below occurs at "the same time in sec", all of mtime, ctime and size are same between (1) and (3). 1. append data to revlog-style file (and close transaction) 2. discard appended data by truncation (strip or rollback) 3. append same size but different data to revlog-style file again Therefore, cache validation doesn't work after (3) as expected. This patch adds file object wrapper class checkambigatclosing to check (and get rid of) ambiguity at closing. It is used by vfs in subsequent patch. This is a part of ExactCacheValidationPlan. https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan BTW, checkambigatclosing is tested in test-filecache.py, even though it doesn't use filecache itself, because filecache assumes that file stat ambiguity never occurs (and there is no another test-*.py related to filecache).
author FUJIWARA Katsunori <foozy@lares.dti.ne.jp>
date Thu, 22 Sep 2016 21:51:57 +0900
parents 0c40e64d6154
children 9766d88c2465
line wrap: on
line diff
--- a/mercurial/scmutil.py	Thu Sep 22 21:51:56 2016 +0900
+++ b/mercurial/scmutil.py	Thu Sep 22 21:51:57 2016 +0900
@@ -1431,3 +1431,34 @@
             return
 
         self._queue.put(fh, block=True, timeout=None)
+
+class checkambigatclosing(closewrapbase):
+    """Proxy for a file object, to avoid ambiguity of file stat
+
+    See also util.filestat for detail about "ambiguity of file stat".
+
+    This proxy is useful only if the target file is guarded by any
+    lock (e.g. repo.lock or repo.wlock)
+
+    Do not instantiate outside of the vfs layer.
+    """
+    def __init__(self, fh):
+        super(checkambigatclosing, self).__init__(fh)
+        object.__setattr__(self, '_oldstat', util.filestat(fh.name))
+
+    def _checkambig(self):
+        oldstat = self._oldstat
+        if oldstat.stat:
+            newstat = util.filestat(self._origfh.name)
+            if newstat.isambig(oldstat):
+                # stat of changed file is ambiguous to original one
+                advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
+                os.utime(self._origfh.name, (advanced, advanced))
+
+    def __exit__(self, exc_type, exc_value, exc_tb):
+        self._origfh.__exit__(exc_type, exc_value, exc_tb)
+        self._checkambig()
+
+    def close(self):
+        self._origfh.close()
+        self._checkambig()