[concurrency-interest] What can an incorrectly synchronized read see?
Maciej.Bobrowski at morganstanley.com
Wed Sep 28 06:47:37 EDT 2016
Right, so the only invalid execution in any possible sequencing is the (1, 0) which was the main question of this post, correct?
From: Concurrency-interest [mailto:concurrency-interest-bounces at cs.oswego.edu] On Behalf Of Aleksey Shipilev
Sent: 28 September 2016 10:01
To: dholmes at ieee.org; concurrency-interest at cs.oswego.edu
Subject: Re: [concurrency-interest] What can an incorrectly synchronized read see?
On 09/28/2016 10:52 AM, David Holmes wrote:
> Is there a typo there Aleksey, the only OK outcome you listed was (0,0). ???
Note that in my note, there are two classes of executions, depending on the sequence of locks/unlocks in (R)eader and (W)riter.
(0, 0): justified by executions with R->W sequencing (0, 1): justified by executions with W->R sequencing (1, 0): is not justified by any executions (1, 1); justified by executions with W->R sequencing
>> -----Original Message-----
>> From: Concurrency-interest [mailto:concurrency-interest-
>> bounces at cs.oswego.edu] On Behalf Of Aleksey Shipilev Note that
>> unsynchronized read can read either "0" or "1", regardless of if
>> synchronized sees "1" after it.
This is for W->R sequencing.
>> Now, let's see what (V1, V2) combinations do not violate JMM:
>> (0, 0) -- ok, both see some (default?) "0" write from before (1, 0)
>> -- NOT OK, r(val):V1 cannot see the w(val,1) that's after in HB!
>> (0, 1) and
>> (1, 1) -- NOT OK for this particular execution, because r(val):V2
>> sees the "future" write w(val,1). Notice, however, that both these
>> results are justified by the execution at the very beginning, when
>> Writer and Reader are sequenced in another order.
This is for R->W sequencing.
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