view mercurial/transaction.py @ 2434:a2df85adface

http server: support persistent connections.

only "hg serve" affected yet.  http server running cgi script will not
use persistent connections.  support for fastcgi will help that.

clients that support keepalive can use one tcp connection for all
commands during clone and pull.  this makes latency of binary search
during pull much lower over wan.

if server does not know content-length, it will force connection to
close at end.  right fix is to use chunked transfer-encoding but this is
easier and does not hurt performance. only command that is affected is
"changegroup" which is always last command during a pull.

# transaction.py - simple journalling scheme for mercurial
#
# This transaction scheme is intended to gracefully handle program
# errors and interruptions. More serious failures like system crashes
# can be recovered with an fsck-like tool. As the whole repository is
# effectively log-structured, this should amount to simply truncating
# anything that isn't referenced in the changelog.
#
# Copyright 2005 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.

import os
from i18n import gettext as _

class transaction(object):
    def __init__(self, report, opener, journal, after=None):
        self.journal = None

        # abort here if the journal already exists
        if os.path.exists(journal):
            raise AssertionError(_("journal already exists - run hg recover"))

        self.count = 1
        self.report = report
        self.opener = opener
        self.after = after
        self.entries = []
        self.map = {}
        self.journal = journal

        self.file = open(self.journal, "w")

    def __del__(self):
        if self.journal:
            if self.entries: self.abort()
            self.file.close()
            try: os.unlink(self.journal)
            except: pass

    def add(self, file, offset, data=None):
        if file in self.map: return
        self.entries.append((file, offset, data))
        self.map[file] = len(self.entries) - 1
        # add enough data to the journal to do the truncate
        self.file.write("%s\0%d\n" % (file, offset))
        self.file.flush()

    def find(self, file):
        if file in self.map:
            return self.entries[self.map[file]]
        return None

    def replace(self, file, offset, data=None):
        if file not in self.map:
            raise KeyError(file)
        index = self.map[file]
        self.entries[index] = (file, offset, data)
        self.file.write("%s\0%d\n" % (file, offset))
        self.file.flush()

    def nest(self):
        self.count += 1
        return self

    def running(self):
        return self.count > 0

    def close(self):
        self.count -= 1
        if self.count != 0:
            return
        self.file.close()
        self.entries = []
        if self.after:
            self.after()
        else:
            os.unlink(self.journal)
        self.journal = None

    def abort(self):
        if not self.entries: return

        self.report(_("transaction abort!\n"))

        for f, o, ignore in self.entries:
            try:
                self.opener(f, "a").truncate(o)
            except:
                self.report(_("failed to truncate %s\n") % f)

        self.entries = []

        self.report(_("rollback completed\n"))

def rollback(opener, file):
    files = {}
    for l in open(file).readlines():
        f, o = l.split('\0')
        files[f] = o
    for f in files:
        o = files[f]
        opener(f, "a").truncate(int(o))
    os.unlink(file)