Fix performance issue for huge repositories

Problem: gitstats will read every commit and every file in repository in one
thread during initial statistics generation (i.e. no cache available). It may
take much time in case of huge repositories (100 000+ files) Solution: Execute
all read commands in 24 threads instead of one

Signed-off-by: Heikki Hokkanen <hoxu@users.sf.net>

gitstats

 import time
 import zlib
 
+if sys.version_info < (2, 6):
+       print >> sys.stderr, "Python 2.6 or higher is required for gitstats"
+       sys.exit(1)
+
+from multiprocessing import Pool
+
 os.environ['LC_ALL'] = 'C'
 
 GNUPLOT_COMMON = 'set terminal png transparent size 640,240\nset size 1.0,1.0\n'
 def getgnuplotversion():
 	return getpipeoutput(['%s --version' % gnuplot_cmd]).split('\n')[0]
 
+def getnumoffilesfromrev(time_rev):
+	"""
+	Get number of files changed in commit
+	"""
+	time, rev = time_rev
+	return (int(time), rev, int(getpipeoutput(['git ls-tree -r --name-only "%s"' % rev, 'wc -l']).split('\n')[0]))
+
+def getnumoflinesinblob(ext_blob):
+	"""
+	Get number of lines in blob
+	"""
+	ext, blob_id = ext_blob
+	return (ext, blob_id, int(getpipeoutput(['git cat-file blob %s' % blob_id, 'wc -l']).split()[0]))
+
 class DataCollector:
 	"""Manages data collection from a revision control repository."""
 	def __init__(self):
 			# timezone
 			self.commits_by_timezone[timezone] = self.commits_by_timezone.get(timezone, 0) + 1
 
-		# TODO Optimize this, it's the worst bottleneck
 		# outputs "<stamp> <files>" for each revision
 		revlines = getpipeoutput(['git rev-list --pretty=format:"%%at %%T" %s' % getcommitrange('HEAD'), 'grep -v ^commit']).strip().split('\n')
 		lines = []
+		revs_to_read = []
+		time_rev_count = []
+		#Look up rev in cache and take info from cache if found
+		#If not append rev to list of rev to read from repo
 		for revline in revlines:
 			time, rev = revline.split(' ')
-			linecount = self.getFilesInCommit(rev)
-			lines.append('%d %d' % (int(time), linecount))
+			#if cache empty then add time and rev to list of new rev's
+			#otherwise try to read needed info from cache
+			if 'files_in_tree' not in self.cache.keys():
+				revs_to_read.append((time,rev))
+				continue
+			if rev in self.cache['files_in_tree'].keys():
+				lines.append('%d %d' % (int(time), self.cache['files_in_tree'][rev]))
+			else:
+				revs_to_read.append((time,rev))
+
+		#Read revisions from repo
+		time_rev_count = Pool(processes=24).map(getnumoffilesfromrev, revs_to_read)
+
+		#Update cache with new revisions and append then to general list
+		for (time, rev, count) in time_rev_count:
+			if 'files_in_tree' not in self.cache:
+				self.cache['files_in_tree'] = {}
+			self.cache['files_in_tree'][rev] = count
+			lines.append('%d %d' % (int(time), count))
 
 		self.total_commits += len(lines)
 		for line in lines:
 
 		# extensions and size of files
 		lines = getpipeoutput(['git ls-tree -r -l -z %s' % getcommitrange('HEAD', end_only = True)]).split('\000')
+		blobs_to_read = []
 		for line in lines:
 			if len(line) == 0:
 				continue
 			if parts[0] == '160000' and parts[3] == '-':
 				# skip submodules
 				continue
-			sha1 = parts[2]
+			blob_id = parts[2]
 			size = int(parts[3])
 			fullpath = parts[4]
 
 				ext = filename[(filename.rfind('.') + 1):]
 			if len(ext) > conf['max_ext_length']:
 				ext = ''
-
 			if ext not in self.extensions:
 				self.extensions[ext] = {'files': 0, 'lines': 0}
-
 			self.extensions[ext]['files'] += 1
-			try:
-				self.extensions[ext]['lines'] += self.getLinesInBlob(sha1)
-			except:
-				print 'Warning: Could not count lines for file "%s"' % line
+			#if cache empty then add ext and blob id to list of new blob's
+			#otherwise try to read needed info from cache
+			if 'lines_in_blob' not in self.cache.keys():
+				blobs_to_read.append((ext,blob_id))
+				continue
+			if blob_id in self.cache['lines_in_blob'].keys():
+				self.extensions[ext]['lines'] += self.cache['lines_in_blob'][blob_id]
+			else:
+				blobs_to_read.append((ext,blob_id))
+
+		#Get info abount line count for new blob's that wasn't found in cache
+		ext_blob_linecount = Pool(processes=24).map(getnumoflinesinblob, blobs_to_read)
+
+		#Update cache and write down info about number of number of lines
+		for (ext, blob_id, linecount) in ext_blob_linecount:
+			if 'lines_in_blob' not in self.cache:
+				self.cache['lines_in_blob'] = {}
+			self.cache['lines_in_blob'][blob_id] = linecount
+			self.extensions[ext]['lines'] += self.cache['lines_in_blob'][blob_id]
 
 		# line statistics
 		# outputs:
 	def getDomains(self):
 		return self.domains.keys()
 	
-	def getFilesInCommit(self, rev):
-		try:
-			res = self.cache['files_in_tree'][rev]
-		except:
-			res = int(getpipeoutput(['git ls-tree -r --name-only "%s"' % rev, 'wc -l']).split('\n')[0])
-			if 'files_in_tree' not in self.cache:
-				self.cache['files_in_tree'] = {}
-			self.cache['files_in_tree'][rev] = res
-
-		return res
-
 	def getFirstCommitDate(self):
 		return datetime.datetime.fromtimestamp(self.first_commit_stamp)
 	
 	def getLastCommitDate(self):
 		return datetime.datetime.fromtimestamp(self.last_commit_stamp)
 	
-	def getLinesInBlob(self, sha1):
-		try:
-			res = self.cache['lines_in_blob'][sha1]
-		except:
-			res = int(getpipeoutput(['git cat-file blob %s' % sha1, 'wc -l']).split()[0])
-			if 'lines_in_blob' not in self.cache:
-				self.cache['lines_in_blob'] = {}
-			self.cache['lines_in_blob'][sha1] = res
-		return res
-
 	def getTags(self):
 		lines = getpipeoutput(['git show-ref --tags', 'cut -d/ -f3'])
 		return lines.split('\n')