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2. Inside of that synchronized method, the consumer calls wait() because
writeable containstrue.Theconsumernowwaitsuntilitreceivesnotifica-
tion from the producer.
3. The producer eventually executes s.setSharedChar(ch); .
4. Whentheproducerentersthatsynchronizedmethod(whichispossiblebecause
theconsumerreleasedthelockinsideofthe wait() methodpriortowaiting),
the producer discovers writeable 's value to be true and does not call
wait() .
5. The producer saves the character, sets writeable to false (which will
causetheproducertowaitonthenext setSharedChar() callwhenthecon-
sumer has not consumed the character by that time), and calls notify() to
awaken the consumer (assuming the consumer is waiting).
6. The producer exits setSharedChar(char c) .
7. Theconsumerwakesup(andreacquiresthelock),sets writeable to true
(whichwillcausetheconsumertowaitonthenext getSharedChar() call
shared character.
Although the synchronization works correctly, you might observe output (on some
platforms) that shows multiple producing messages before a consuming message. For
example,youmightsee A produced by producer. ,followedby B produced
by producer. ,followedby A consumed by consumer. ,atthebeginningof
the application's output.
Thisstrangeoutputorderiscausedbythecallto setSharedChar() followedby
its companion System.out.println() method call not being atomic, and by the
callto getSharedChar() followedbyitscompanion System.out.println()
method call not being atomic. The output order is corrected by wrapping each of
these method call pairs in a synchronized block that synchronizes on the s -referenced
Shared object.
order, as shown next (only the first few lines are shown for brevity):
A produced by producer.
A consumed by consumer.
B produced by producer.
B consumed by consumer.
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