--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/appendfile.py Fri Mar 24 09:23:11 2006 -0800
@@ -0,0 +1,171 @@
+# appendfile.py - special classes to make repo updates atomic
+#
+# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
+#
+# This software may be used and distributed according to the terms
+# of the GNU General Public License, incorporated herein by reference.
+
+from demandload import *
+demandload(globals(), "cStringIO changelog manifest os tempfile")
+
+# writes to metadata files are ordered. reads: changelog, manifest,
+# normal files. writes: normal files, manifest, changelog.
+
+# manifest contains pointers to offsets in normal files. changelog
+# contains pointers to offsets in manifest. if reader reads old
+# changelog while manifest or normal files are written, it has no
+# pointers into new parts of those files that are maybe not consistent
+# yet, so will not read them.
+
+# localrepo.addchangegroup thinks it writes changelog first, then
+# manifest, then normal files (this is order they are available, and
+# needed for computing linkrev fields), but uses appendfile to hide
+# updates from readers. data not written to manifest or changelog
+# until all normal files updated. write manifest first, then
+# changelog.
+
+# with this write ordering, readers cannot see inconsistent view of
+# repo during update.
+
+class appendfile(object):
+ '''implement enough of file protocol to append to revlog file.
+ appended data is written to temp file. reads and seeks span real
+ file and temp file. readers cannot see appended data until
+ writedata called.'''
+
+ def __init__(self, fp):
+ fd, self.tmpname = tempfile.mkstemp()
+ self.tmpfp = os.fdopen(fd, 'ab+')
+ self.realfp = fp
+ self.offset = 0
+ # real file is not written by anyone else. cache its size so
+ # seek and read can be fast.
+ self.fpsize = os.fstat(fp.fileno()).st_size
+
+ def seek(self, offset):
+ '''virtual file offset spans real file and temp file.'''
+ self.offset = offset
+ if self.offset < self.fpsize:
+ self.realfp.seek(self.offset)
+ else:
+ self.tmpfp.seek(self.offset - self.fpsize)
+
+ def read(self, count=-1):
+ '''only trick here is reads that span real file and temp file.'''
+ fp = cStringIO.StringIO()
+ old_offset = self.offset
+ if self.offset < self.fpsize:
+ s = self.realfp.read(count)
+ fp.write(s)
+ self.offset += len(s)
+ if count > 0:
+ count -= len(s)
+ if count != 0:
+ if old_offset != self.offset:
+ self.tmpfp.seek(self.offset - self.fpsize)
+ s = self.tmpfp.read(count)
+ fp.write(s)
+ self.offset += len(s)
+ return fp.getvalue()
+
+ def write(self, s):
+ '''append to temp file.'''
+ self.tmpfp.write(s)
+ # all writes are appends, so offset must go to end of file.
+ self.offset = self.fpsize + self.tmpfp.tell()
+
+ def writedata(self):
+ '''copy data from temp file to real file.'''
+ self.tmpfp.seek(0)
+ s = self.tmpfp.read()
+ self.tmpfp.close()
+ self.realfp.seek(0, 2)
+ # small race here. we write all new data in one call, but
+ # reader can see partial update due to python or os. file
+ # locking no help: slow, not portable, not reliable over nfs.
+ # only safe thing is write to temp file every time and rename,
+ # but performance bad when manifest or changelog gets big.
+ self.realfp.write(s)
+ self.realfp.close()
+
+ def __del__(self):
+ '''delete temp file even if exception raised.'''
+ try: os.unlink(self.tmpname)
+ except: pass
+
+class sharedfile(object):
+ '''let file objects share a single appendfile safely. each
+ sharedfile has own offset, syncs up with appendfile offset before
+ read and after read and write.'''
+
+ def __init__(self, fp):
+ self.fp = fp
+ self.offset = 0
+
+ def seek(self, offset):
+ self.offset = offset
+
+ def read(self, count=-1):
+ try:
+ if self.offset != self.fp.offset:
+ self.fp.seek(self.offset)
+ return self.fp.read(count)
+ finally:
+ self.offset = self.fp.offset
+
+ def write(self, s):
+ try:
+ return self.fp.write(s)
+ finally:
+ self.offset = self.fp.offset
+
+ def close(self):
+ # revlog wants this.
+ pass
+
+ def flush(self):
+ # revlog wants this.
+ pass
+
+ def writedata(self):
+ self.fp.writedata()
+
+class appendopener(object):
+ '''special opener for files that only read or append.'''
+
+ def __init__(self, opener):
+ self.realopener = opener
+ # key: file name, value: appendfile object
+ self.fps = {}
+
+ def __call__(self, name, mode='r'):
+ '''open file. return same cached appendfile object for every
+ later call.'''
+
+ assert mode in 'ra'
+ fp = self.fps.get(name)
+ if fp is None:
+ fp = appendfile(self.realopener(name, 'a+'))
+ self.fps[name] = fp
+ return sharedfile(fp)
+
+ def writedata(self):
+ '''copy data from temp files to real files.'''
+ # write .d file before .i file.
+ fps = self.fps.items()
+ fps.sort()
+ for name, fp in fps:
+ fp.writedata()
+
+# files for changelog and manifest are in different appendopeners, so
+# not mixed up together.
+
+class appendchangelog(changelog.changelog, appendopener):
+ def __init__(self, opener):
+ appendopener.__init__(self, opener)
+ changelog.changelog.__init__(self, self)
+
+class appendmanifest(manifest.manifest, appendopener):
+ def __init__(self, opener):
+ appendopener.__init__(self, opener)
+ manifest.manifest.__init__(self, self)