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<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">we have a question about the interaction between G1 post barriers and the refinement thread's concurrent dirty card cleaning.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">The case in which the G1 post barrier sees a clean card is obviously not problematic, because it will add an entry in a dirty card queue.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">However, in case in which the Java thread (mutator thread) sees the card already dirtied, it won’t enqueue the card again. Which is safe as long as its stored
oop (1) is seen and processed (3’) by the parallel refinement after having cleaned the card (1’):<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">Java Thread (mutator) Refinement Thread (G1RemSet::concurrentRefineOneCard_impl calls oops_on_card_seq_iterate_careful)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">(1) store(oop)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">( StoreLoad required here ?)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">(2) load(card==dirty)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""> (1’) store(card==clean)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""> (2’) StoreLoad barrier<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""> (3’) load(oop)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">So the refinement thread seems to rely on getting the oop which was written BEFORE the (2) load(card==dirty) was observed.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">We wonder how this ordering is guaranteed? There are no StoreLoad barriers in the Java Thread's path. (StoreLoad ordering needs explicit barriers even on TSO
platforms.)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-family:"Courier New"">Kind regards,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Courier New"">Martin<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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