> I think the issue here is more the ConcurrentHashMap that doesn't promise you'll get both entries when calling c.values() in either one of the threads.
What do you mean? poniedziałek, 12 września 2022 o 17:44:31 UTC+2 [email protected] napisał(a): > I think the issue here is more the ConcurrentHashMap that doesn't promise > you'll get both entries when calling c.values() in either one of the > threads. > > On Monday, September 12, 2022 at 7:50:56 AM UTC-7 [email protected] wrote: > >> Thanks, for your response. I know that output "true" is possible. My >> question is: Is it guaranteed by JMM that one of T1, T2 will print "true, >> true"? >> >> pon., 12 wrz 2022, 15:11 użytkownik Peter Veentjer <[email protected]> >> napisał: >> >>> I think this example is better: >>> >>> class Foo{ >>> int x; >>> } >>> >>> Thread1: >>> Foo foo = new Foo(); >>> foo.x = 10; (1) >>> concurrentMap.put("1", foo); (2) >>> >>> Thread2: >>> Foo foo = concurrentMap.get("1"); (3) >>> if(foo!=null) print(foo.x); (4) >>> >>> There is a happens-before edge between (1) and (2) due to program-order >>> rule. And also between (3) and (4) there is a happens-before edge due to >>> program-order rule. >>> >>> And if thread2 sees the non null value, then there is a happens-before >>> edge between (2) and (3) due to either the volatile variable rule or >>> monitor lock rule (often this is called memory consistency effects on e.g. >>> queues) >>> >>> Since the happens-before relation is transitive, there is a >>> happens-before edge between (1) and (4). >>> >>> On Mon, Sep 12, 2022 at 4:02 PM Alper Tekinalp <[email protected]> >>> wrote: >>> >>>> From util.concurrent: >>>> >>>> > Actions in a thread prior to placing an object into any concurrent >>>> collection happen-before actions subsequent to the access or removal of >>>> that element from the collection in another thread. >>>> >>>> So ether one of threads will print (true, true) I guess. >>>> >>>> On Mon, Sep 12, 2022, 3:42 PM Peter Veentjer <[email protected]> >>>> wrote: >>>> >>>>> If T1 would run first, the content of the ConcurrentHashMap is >>>>> (1,true), and therefore there is only 1 value. >>>>> >>>>> So it will print 'true' and not 'true,true' because T2 has not run yet. >>>>> >>>>> On Mon, Sep 12, 2022 at 3:31 PM r r <[email protected]> wrote: >>>>> >>>>>> Hello, >>>>>> let's look for the following piece of code: >>>>>> >>>>>> c = new ConcurrentHashMap<Integer, Boolean>(); >>>>>> T1: >>>>>> c.put(1, true); >>>>>> for (Boolean b : c.values()) { >>>>>> print(b); >>>>>> } >>>>>> T2: >>>>>> c.put(2, true); >>>>>> for (Boolean b : c.values()) { >>>>>> print(b); >>>>>> } >>>>>> >>>>>> Is it guaranteed by JMM that any thread (T1 or T2) prints true, true? >>>>>> To put it in another way, is it guaranteed that T1 or T2 observes >>>>>> both c.put? >>>>>> >>>>>> If yes / no, why? >>>>>> Thanks in advance for your time. >>>>>> >>>>>> -- >>>>>> 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]. >>>>>> To view this discussion on the web, visit >>>>>> https://groups.google.com/d/msgid/mechanical-sympathy/0945e8e3-1070-4166-b269-1c4e6c49da3en%40googlegroups.com >>>>>> >>>>>> <https://groups.google.com/d/msgid/mechanical-sympathy/0945e8e3-1070-4166-b269-1c4e6c49da3en%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> >>>>> -- >>>>> 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]. >>>>> To view this discussion on the web, visit >>>>> https://groups.google.com/d/msgid/mechanical-sympathy/CAGuAWdAzirHPwyj%2B55%3D%2BSvkcLbKg80wzgspu8CDOGHOMD0Zchg%40mail.gmail.com >>>>> >>>>> <https://groups.google.com/d/msgid/mechanical-sympathy/CAGuAWdAzirHPwyj%2B55%3D%2BSvkcLbKg80wzgspu8CDOGHOMD0Zchg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >>>> 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]. >>>> To view this discussion on the web, visit >>>> https://groups.google.com/d/msgid/mechanical-sympathy/CABKpSe5Z5ns%2BJ0O8cd-z0%2B%3DSgj75gr65LXbSur6W3BaELebN-A%40mail.gmail.com >>>> >>>> <https://groups.google.com/d/msgid/mechanical-sympathy/CABKpSe5Z5ns%2BJ0O8cd-z0%2B%3DSgj75gr65LXbSur6W3BaELebN-A%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- >>> 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]. >>> >> To view this discussion on the web, visit >>> https://groups.google.com/d/msgid/mechanical-sympathy/CAGuAWdCPKSx5c0wj2mdXkg%3DHm1b4H65ZTx1K_vJ7d9P4KC2q4w%40mail.gmail.com >>> >>> <https://groups.google.com/d/msgid/mechanical-sympathy/CAGuAWdCPKSx5c0wj2mdXkg%3DHm1b4H65ZTx1K_vJ7d9P4KC2q4w%40mail.gmail.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. 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