convert: when getting file from Perforce concatenate data at the end

As it turned out, even when getting relatively small files, concatenating
string data every time when new chunk is received is very inefficient.
Maintaining a string list of data chunks and concatenating everything in one go
at the end seems much more efficient - in my testing it made getting 40 MB file
7 times faster, whilst converting of a particularly big changelist with some big
files went down from 20 hours to 3 hours.

hgext/convert/p4.py

@@ -1,284 +1,286 b''
 # Perforce source for convert extension.
 #
 # Copyright 2009, Frank Kingswood <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from mercurial import util
 from mercurial.i18n import _
 
 from common import commit, converter_source, checktool, NoRepo
 import marshal
 import re
 
 def loaditer(f):
     "Yield the dictionary objects generated by p4"
     try:
         while True:
             d = marshal.load(f)
             if not d:
                 break
             yield d
     except EOFError:
         pass
 
 def decodefilename(filename):
     """Perforce escapes special characters @, #, *, or %
     with %40, %23, %2A, or %25 respectively
 
     >>> decodefilename('portable-net45%252Bnetcore45%252Bwp8%252BMonoAndroid')
     'portable-net45%2Bnetcore45%2Bwp8%2BMonoAndroid'
     >>> decodefilename('//Depot/Directory/%2525/%2523/%23%40.%2A')
     '//Depot/Directory/%25/%23/#@.*'
     """
     replacements = [('%2A', '*'), ('%23', '#'), ('%40', '@'), ('%25', '%')]
     for k, v in replacements:
         filename = filename.replace(k, v)
     return filename
 
 class p4_source(converter_source):
     def __init__(self, ui, path, revs=None):
         super(p4_source, self).__init__(ui, path, revs=revs)
 
         if "/" in path and not path.startswith('//'):
             raise NoRepo(_('%s does not look like a P4 repository') % path)
 
         checktool('p4', abort=False)
 
         self.p4changes = {}
         self.heads = {}
         self.changeset = {}
         self.files = {}
         self.copies = {}
         self.tags = {}
         self.lastbranch = {}
         self.parent = {}
         self.encoding = "latin_1"
         self.depotname = {}           # mapping from local name to depot name
         self.localname = {} # mapping from depot name to local name
         self.re_type = re.compile(
             "([a-z]+)?(text|binary|symlink|apple|resource|unicode|utf\d+)"
             "(\+\w+)?$")
         self.re_keywords = re.compile(
             r"\$(Id|Header|Date|DateTime|Change|File|Revision|Author)"
             r":[^$\n]*\$")
         self.re_keywords_old = re.compile("\$(Id|Header):[^$\n]*\$")
 
         if revs and len(revs) > 1:
             raise util.Abort(_("p4 source does not support specifying "
                                "multiple revisions"))
         self._parse(ui, path)
 
     def _parse_view(self, path):
         "Read changes affecting the path"
         cmd = 'p4 -G changes -s submitted %s' % util.shellquote(path)
         stdout = util.popen(cmd, mode='rb')
         for d in loaditer(stdout):
             c = d.get("change", None)
             if c:
                 self.p4changes[c] = True
 
     def _parse(self, ui, path):
         "Prepare list of P4 filenames and revisions to import"
         ui.status(_('reading p4 views\n'))
 
         # read client spec or view
         if "/" in path:
             self._parse_view(path)
             if path.startswith("//") and path.endswith("/..."):
                 views = {path[:-3]:""}
             else:
                 views = {"//": ""}
         else:
             cmd = 'p4 -G client -o %s' % util.shellquote(path)
             clientspec = marshal.load(util.popen(cmd, mode='rb'))
 
             views = {}
             for client in clientspec:
                 if client.startswith("View"):
                     sview, cview = clientspec[client].split()
                     self._parse_view(sview)
                     if sview.endswith("...") and cview.endswith("..."):
                         sview = sview[:-3]
                         cview = cview[:-3]
                     cview = cview[2:]
                     cview = cview[cview.find("/") + 1:]
                     views[sview] = cview
 
         # list of changes that affect our source files
         self.p4changes = self.p4changes.keys()
         self.p4changes.sort(key=int)
 
         # list with depot pathnames, longest first
         vieworder = views.keys()
         vieworder.sort(key=len, reverse=True)
 
         # handle revision limiting
         startrev = self.ui.config('convert', 'p4.startrev', default=0)
         self.p4changes = [x for x in self.p4changes
                           if ((not startrev or int(x) >= int(startrev)) and
                               (not self.revs or int(x) <= int(self.revs[0])))]
 
         # now read the full changelists to get the list of file revisions
         ui.status(_('collecting p4 changelists\n'))
         lastid = None
         for change in self.p4changes:
             cmd = "p4 -G describe -s %s" % change
             stdout = util.popen(cmd, mode='rb')
             d = marshal.load(stdout)
             desc = self.recode(d.get("desc", ""))
             shortdesc = desc.split("\n", 1)[0]
             t = '%s %s' % (d["change"], repr(shortdesc)[1:-1])
             ui.status(util.ellipsis(t, 80) + '\n')
 
             if lastid:
                 parents = [lastid]
             else:
                 parents = []
 
             date = (int(d["time"]), 0)     # timezone not set
             c = commit(author=self.recode(d["user"]),
                        date=util.datestr(date, '%Y-%m-%d %H:%M:%S %1%2'),
                        parents=parents, desc=desc, branch=None,
                        extra={"p4": change})
 
             files = []
             copies = {}
             copiedfiles = []
             i = 0
             while ("depotFile%d" % i) in d and ("rev%d" % i) in d:
                 oldname = d["depotFile%d" % i]
                 filename = None
                 for v in vieworder:
                     if oldname.lower().startswith(v.lower()):
                         filename = decodefilename(views[v] + oldname[len(v):])
                         break
                 if filename:
                     files.append((filename, d["rev%d" % i]))
                     self.depotname[filename] = oldname
                     if (d.get("action%d" % i) == "move/add"):
                         copiedfiles.append(filename)
                     self.localname[oldname] = filename
                 i += 1
 
             # Collect information about copied files
             for filename in copiedfiles:
                 oldname = self.depotname[filename]
 
                 flcmd = 'p4 -G filelog %s' \
                       % util.shellquote(oldname)
                 flstdout = util.popen(flcmd, mode='rb')
 
                 copiedfilename = None
                 for d in loaditer(flstdout):
                     copiedoldname = None
 
                     i = 0
                     while ("change%d" % i) in d:
                         if (d["change%d" % i] == change and
                             d["action%d" % i] == "move/add"):
                             j = 0
                             while ("file%d,%d" % (i, j)) in d:
                                 if d["how%d,%d" % (i, j)] == "moved from":
                                     copiedoldname = d["file%d,%d" % (i, j)]
                                     break
                                 j += 1
                         i += 1
 
                     if copiedoldname and copiedoldname in self.localname:
                         copiedfilename = self.localname[copiedoldname]
                         break
 
                 if copiedfilename:
                     copies[filename] = copiedfilename
                 else:
                     ui.warn(_("cannot find source for copied file: %s@%s\n")
                             % (filename, change))
 
             self.changeset[change] = c
             self.files[change] = files
             self.copies[change] = copies
             lastid = change
 
         if lastid:
             self.heads = [lastid]
 
     def getheads(self):
         return self.heads
 
     def getfile(self, name, rev):
         cmd = 'p4 -G print %s' \
             % util.shellquote("%s#%s" % (self.depotname[name], rev))
 
         lasterror = None
         while True:
             stdout = util.popen(cmd, mode='rb')
 
             mode = None
-            contents = ""
+            contents = []
             keywords = None
 
             for d in loaditer(stdout):
                 code = d["code"]
                 data = d.get("data")
 
                 if code == "error":
                     # if this is the first time error happened
                     # re-attempt getting the file
                     if not lasterror:
                         lasterror = IOError(d["generic"], data)
                         # this will exit inner-most for-loop
                         break
                     else:
                         raise lasterror
 
                 elif code == "stat":
                     action = d.get("action")
                     if action in ["purge", "delete", "move/delete"]:
                         return None, None
                     p4type = self.re_type.match(d["type"])
                     if p4type:
                         mode = ""
                         flags = ((p4type.group(1) or "")
                                + (p4type.group(3) or ""))
                         if "x" in flags:
                             mode = "x"
                         if p4type.group(2) == "symlink":
                             mode = "l"
                         if "ko" in flags:
                             keywords = self.re_keywords_old
                         elif "k" in flags:
                             keywords = self.re_keywords
 
                 elif code == "text" or code == "binary":
-                    contents += data
+                    contents.append(data)
 
                 lasterror = None
 
             if not lasterror:
                 break
 
         if mode is None:
             return None, None
 
+        contents = ''.join(contents)
+
         if keywords:
             contents = keywords.sub("$\\1$", contents)
         if mode == "l" and contents.endswith("\n"):
             contents = contents[:-1]
 
         return contents, mode
 
     def getchanges(self, rev, full):
         if full:
             raise util.Abort(_("convert from p4 do not support --full"))
         return self.files[rev], self.copies[rev], set()
 
     def getcommit(self, rev):
         return self.changeset[rev]
 
     def gettags(self):
         return self.tags
 
     def getchangedfiles(self, rev, i):
         return sorted([x[0] for x in self.files[rev]])