Python多进程分块读取超大文件的方法

# -*- coding: GBK -*-import urlparseimport datetimeimport osfrom multiprocessing import Process,Queue,Array,RLock"""多进程分块读取文件"""WORKERS = 4BLOCKSIZE = 100000000FILE_SIZE = 0def 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"  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()