python多进程分块读取文件

# -*- coding: GBK -*-
# filename: multiprocessreadfile.py

import urlparse
import datetime
import os
from multiprocessing import Process,Queue,Array,RLock

"""
多进程分块读取文件
"""

WORKERS = 4
BLOCKSIZE = 100000000 #字节，接近100MB
FILE_SIZE = 0

def getFilesize(file):
"""
获取要读取文件的大小
"""
global FILE_SIZE
fstream = open(file,'r')
fstream.seek(0,os.SEEK_END)
FILE_SIZE = fstream.tell()
fstream.close()

def process_found(pid,array,file,rlock):
global FILE_SIZE
global JOB
global PREFIX
"""
进程处理
Args:
pid:进程编号
array:进程间共享队列，用于标记各进程所读的文件块结束位置
file:所读文件名称
各个进程先从array中获取当前最大的值为起始位置startpossition
结束的位置endpossition (startpossition+BLOCKSIZE) if (startpossition+BLOCKSIZE)<FILE_SIZE else FILE_SIZE
if startpossition==FILE_SIZE则进程结束
if startpossition==0则从0开始读取
if startpossition!=0为防止行被block截断的情况，先读一行不处理，从下一行开始正式处理
if 当前位置 <=endpossition 就readline
否则越过边界，就从新查找array中的最大值
"""
fstream = open(file,'r')

while True:
rlock.acquire()
print 'pid%s'%pid,','.join([str(v) for v in array])
startpossition = max(array)
endpossition = array[pid] = (startpossition+BLOCKSIZE) if (startpossition+BLOCKSIZE)<FILE_SIZE else FILE_SIZE
rlock.release()

if startpossition == FILE_SIZE:#end of the file
print 'pid%s end'%(pid)
break
elif startpossition !=0:
fstream.seek(startpossition)
fstream.readline()
pos = ss = fstream.tell()
ostream = open('/data/download/tmp_pid'+str(pid)+'_jobs'+str(endpossition),'w')
while pos<endpossition:
#处理line
line = fstream.readline()
ostream.write(line)
pos = fstream.tell()

print 'pid:%s,startposition:%s,endposition:%s,pos:%s'%(pid,ss,pos,pos)
ostream.flush()
ostream.close()
ee = fstream.tell()

fstream.close()

def main():
global FILE_SIZE
print datetime.datetime.now().strftime("%Y/%d/%m %H:%M:%S")

#    file = "/data/pds/download/scmcc_log/tmp_format_2011004.log"
file = "zdmm1_10.txt"
getFilesize(file)
print FILE_SIZE

rlock = RLock()
array = Array('l',WORKERS,lock=rlock)
threads=[]
for i in range(WORKERS):
p=Process(target=process_found, args=[i,array,file,rlock])
threads.append(p)

for i in range(WORKERS):
threads[i].start()

for i in range(WORKERS):
threads[i].join()

print datetime.datetime.now().strftime("%Y/%d/%m %H:%M:%S")

if __name__ == '__main__':
main()