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List:       python-list
Subject:    Re: collect data using threads
From:       Kent Johnson <kent37 () tds ! net>
Date:       2005-06-14 14:53:20
Message-ID: 42aeeef3$1_1 () newspeer2 ! tds ! net
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Peter Hansen wrote:
> Qiangning Hong wrote:
> 
> > A class Collector, it spawns several threads to read from serial port.
> > Collector.get_data() will get all the data they have read since last
> > call.  Who can tell me whether my implementation correct?
> 
> [snip sample with a list]
> 
> > I am not very sure about the get_data() method.  Will it cause data lose
> > if there is a thread is appending data to self.data at the same time?
> 
> 
> That will not work, and you will get data loss, as Jeremy points out.
> 
> Normally Python lists are safe, but your key problem (in this code) is 
> that you are rebinding self.data to a new list!  If another thread calls 
> on_received() just after the line "x = self.data" executes, then the new 
> data will never be seen.

Can you explain why not? self.data is still bound to the same list as x. At least if \
the execution sequence is  x = self.data
                    self.data.append(a_piece_of_data)
self.data = []

ISTM it should work.

I'm not arguing in favor of the original code, I'm just trying to understand your \
specific failure mode.

Thanks,
Kent
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