transaction: separate calculating TXNID from creating transaction object
Before this patch, transaction ID (TXNID) is calculated from
`transaction` object itself by `id()`, but this prevents TXNID from
being passed to `pretxnopen` hooks, which should be executed before
starting transaction processing (also any preparations for it, like
writing journal files out).
As a preparation for passing TXNID to `pretxnopen` hooks, this patch
separates calculation of TXNID from creation of `transaction` object.
This patch uses "random" library for reasonable unique ID. "uuid"
library can't be used, because it was introduced since Python 2.5 and
isn't suitable for Mercurial 3.4.x stable line.
`%f` formatting for `random.random()` is used with explicit precision
number 40, because default precision for `%f` is 6. 40 should be long
enough, even if 10**9 transactions are executed in a short time (a
second or less).
On the other hand, `time.time()` is used to ensures uniqueness of
TXNID in a long time, for safety.
BTW, platform not providing `/dev/urandom` or so may cause failure of
`import random` itself with some Python versions (see Python
issue15340 for detail http://bugs.python.org/issue15340).
But this patch uses "random" without any workaround, because:
- "random" is already used directly in some code paths,
- such platforms are very rare (e.g. Tru64 and HPUX), and
http://bugs.python.org/issue15340#msg170000
- updating Python runtime can avoid this issue
Test how largefiles abort in case the disk runs full
$ cat > criple.py <<EOF
> import os, errno, shutil
> from mercurial import util
> #
> # this makes the original largefiles code abort:
> def copyfileobj(fsrc, fdst, length=16*1024):
> fdst.write(fsrc.read(4))
> raise IOError(errno.ENOSPC, os.strerror(errno.ENOSPC))
> shutil.copyfileobj = copyfileobj
> #
> # this makes the rewritten code abort:
> def filechunkiter(f, size=65536, limit=None):
> yield f.read(4)
> raise IOError(errno.ENOSPC, os.strerror(errno.ENOSPC))
> util.filechunkiter = filechunkiter
> #
> def oslink(src, dest):
> raise OSError("no hardlinks, try copying instead")
> util.oslink = oslink
> EOF
$ echo "[extensions]" >> $HGRCPATH
$ echo "largefiles =" >> $HGRCPATH
$ hg init alice
$ cd alice
$ echo "this is a very big file" > big
$ hg add --large big
$ hg commit --config extensions.criple=$TESTTMP/criple.py -m big
abort: No space left on device
[255]
The largefile is not created in .hg/largefiles:
$ ls .hg/largefiles
dirstate
The user cache is not even created:
>>> import os; os.path.exists("$HOME/.cache/largefiles/")
False
Make the commit with space on the device:
$ hg commit -m big
Now make a clone with a full disk, and make sure lfutil.link function
makes copies instead of hardlinks:
$ cd ..
$ hg --config extensions.criple=$TESTTMP/criple.py clone --pull alice bob
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
updating to branch default
getting changed largefiles
abort: No space left on device
[255]
The largefile is not created in .hg/largefiles:
$ ls bob/.hg/largefiles
dirstate