Bill Pugh wrote:
> >>For example, consider:
> >>
> >>Initially, x = y = 0
> >>
> >>Thread 1:
> >> if x != 0
> >> y = 1
> >>
> >>Thread 2:
> >> if y != 0
> >> x = 1
> >>
> >>You must be careful to not allow this program to result in
> x = 1 and y
> >>= 1.
> >>
> >> Bill
> >>-------------------------------
> >>JavaMemoryModel mailing list -
> >>http://www.cs.umd.edu/~pugh/java/memoryModel
> >
> >
> >Why not? No, I'm not arguing that this should be allowed.
> >I just want to hear your reasons why This Is Bad.
> >
> >Cliff
>
> This program is correctly synchronized and therefore must execute
> according to sequentially consistent semantics.
>
> The basic definition of "correctly synchronized" is, for all
> sequentially consistent executions of the program, an ordering
> consistent exists between any two conflicting accesses to a variable.
>
> There is only one sequentially consistent execution of this program,
> in which each thread reads one variable and doesn't write any. So
> there are no conflicting accesses, and the only execution allowed is
> the sequentially consistent one.
>
> Bill
Perhaps this is a silly question, but is it a foregone conclusion that
all multi-threaded but unsynchronized Java programs are sequentially
consistent? That seems to be implied by the above analysis.
- Roly
Roly Perera
Ergnosis Ltd
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