Databases
StackOverflow2013
Postsdbo
POQueueing work, without using a lot of memory
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POQueueing work, without using a lot of memory
    primarykey
    data
    text
    <p>I'm trying to set something up where one thread is writing a list of work and another thread is reading the list and working from it. This list can be very large so to stop this list being held in memory I want to have it written in a file (or anyway of preserving memory- generators?).</p> <p>I put together a little runnable example with a sleep in the writer so that the reader can catch up. I'm wondering how I can get the reader to not stop when it "overtakes" the writer. I looked at using <code>.seek</code> and <code>.tell</code> but I got weird behaviour and I'm not sure that's the right route.</p> <p>As another question, is this at all a sensible idea? Maybe there's a much more elegant way I can queue up a list of strings without using loads of memory.</p> <pre><code>import threading,time class Writer(threading.Thread): lock= threading.Lock() def __init__(self,file_path,size): threading.Thread.__init__(self) self.file_path= file_path self.size= size self.i=0 def how_many(self): with self.lock: print "Reader starting, writer is on",self.i def run(self): f=open(self.file_path,"w") for i in xrange(self.size): with self.lock: self.i=i if i%1000==0: time.sleep(0.1) f.write("%s\n"%i) f.close() class Reader(threading.Thread): def __init__(self,file_path): threading.Thread.__init__(self) self.file_path= file_path def run(self): f=open(self.file_path,"r") line=0 for line in f: pass print "Reader got to: %s"%line.strip() if __name__ == "__main__": a= Writer("testfile",2000000) b= Reader("testfile") a.start() time.sleep(1) a.how_many() b.start() </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USGP89
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POQueueing work, without using a lot of memory
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POQueueing work, without using a lot of memory
      1. This table or related slice is empty.
      1. VTUpMod
    1. COHave you looked into [pipes](http://stackoverflow.com/questions/1430446/create-a-temporary-fifo-named-pipe-in-python)?
      singulars
      1. POQueueing work, without using a lot of memory
      1. USSpencer Rathbun
    2. COLooks promising but this is UNIX only right? I need something that will be platform independent unfortunately
      singulars
      1. POQueueing work, without using a lot of memory
      1. USGP89
    3. COCheck [here](http://eli.thegreenplace.net/2011/12/27/python-threads-communication-and-stopping/) for an example of worker threads and queues in python. The Queue.Queue class handles creating fifo pipes cross-platform. You may need to subclass the queue to write entries to a temp file, for your memory issue.
      singulars
      1. POQueueing work, without using a lot of memory
      1. USSpencer Rathbun
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload