This is all too confusing… can’t you just single thread everything? — Kirk
> On Nov 18, 2018, at 10:35 AM, Vladimir Sitnikov <[email protected]> > wrote: > > Jean-Philippe>is a write to value but no read of this value inside the same > thread, so the write is free to be reordered > > It ("reordering") does not really matter. > > For instance, > > 17.4.5. Happens-before Order> If the reordering produces results consistent > with a legal execution, it is not illegal. > > What matters is the set of possible "writes" that given "read" is allowed to > observe. > > > In this case, simple transitivity is enough to establish hb. > As Gil highlights, "negations" are a bit hard to deal with, and Mr.Alexey > converts the negations to a positive clauses: > https://shipilev.net/blog/2014/jmm-pragmatics/#_happens_before > <https://shipilev.net/blog/2014/jmm-pragmatics/#_happens_before> > > Shipilёv> Therefore, in the absence of races, we can only see the latest > write in HB. > > Note: we (as programmers) do not really care HOW the runtime and/or CPU would > make that possible. We have guarantees from JVM that "in the absence of > races, we can only see the latest write in HB". > CPU can reorder things and/or execute multiple instructions in parallel. I > don't really need to know the way it is implemented in order to prove that > "CHM is fine to share objects across threads". > > Just in case: there are two writes for w.value field. > "write1" is "the write of default value" which "synchronizes-with the first > action in every thread" (see 17.4.4.) + "If an action x synchronizes-with a > following action y, then we also have hb(x, y)." (see 17.4.5) > "write2" is "w.value=42" > > "value=0" (write1) happens-before "w.value=42" (write2) by definition > (17.4.4+17.4.5) > w.value=42 happens-before map.put (program order implies happens-before) > read of u.value happens-before map.put (CHM guarantees that) > > In other words, "w.value=42" is the latest write in hb order for u.value > read, so u.value must observe 42. > JRE must ensure that the only possible outcome for the program in question is > 42. > > Vladimir > > -- > You received this message because you are subscribed to the Google Groups > "mechanical-sympathy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > <mailto:[email protected]>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
