<div dir="ltr"><div class="markdown-here-wrapper" style=""><p style="margin:0px 0px 1.2em!important">It looks pretty inconsistent to have the API of the structured concurrency and of ExtentLocal have different design, especially when it seems like the 2 APIs have the same base assumptions.</p>
<p style="margin:0px 0px 1.2em!important">From my understanding those 2 features are meant for each other. I actually agree that allowing “weak” TwR for ExtentLocals is probably a bad idea, but I also believe the same for structured concurrency:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code class="hljs language-java" style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;color:rgb(51,51,51);background:rgb(248,248,248)"> <span class="hljs-function"><span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">void</span> <span class="hljs-title" style="color:rgb(153,0,0);font-weight:bold">foo</span><span class="hljs-params">()</span> </span>{
var scope = <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">new</span> StructuredTaskScope.ShutdownOnFailure();
var scope1 = <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">new</span> StructuredTaskScope.ShutdownOnFailure();
scope.close();
scope1.close();
}
</code></pre>
<p style="margin:0px 0px 1.2em!important">This should fail on compile time.</p>
<p style="margin:0px 0px 1.2em!important">This is less important for the incubator, but for the preview I do think it is important to prevent weird bugs when people misusing the feature.<br>For example, I can see someone without understanding of structured concurrency writing the following:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code class="hljs language-java" style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;color:rgb(51,51,51);background:rgb(248,248,248)"><span class="hljs-comment" style="color:rgb(153,153,136);font-style:italic">// abstraction of a calculation on "int[]" that can be partitioned and then aggregated into a single result</span>
<span class="hljs-comment" style="color:rgb(153,153,136);font-style:italic">// contains "int set/setCount()" for the count of partitions, a method "void calcPart(int[] lst, int partNumber)", "void aggregateParts()" and "int getResult()"</span>
<span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">public</span> <span class="hljs-class"><span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">interface</span> <span class="hljs-title" style="color:rgb(153,0,0);font-weight:bold;color:rgb(68,85,136);font-weight:bold">PartitiableAction</span> </span>{ ... }
...
<span class="hljs-function"><span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">public</span> <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">static</span> <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">void</span> <span class="hljs-title" style="color:rgb(153,0,0);font-weight:bold">calcAtOnce</span><span class="hljs-params">(Collection<PartitiableAction> actions, <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">int</span>[] input)</span> </span>{
var scopes = <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">new</span> HashMap<PartitiableAction, StructuredTaskScope.ShutdownOnFailure>();
<span class="hljs-comment" style="color:rgb(153,153,136);font-style:italic">// start a scope for each action</span>
<span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">for</span> (var action : actions) {
var scope = <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">new</span> StructuredTaskScope.ShutdownOnFailure();
scopes.put(action, scope);
<span class="hljs-comment" style="color:rgb(153,153,136);font-style:italic">// new thread for each part of the calculation</span>
<span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">for</span> (var j = <span class="hljs-number" style="color:rgb(0,128,128)">0</span>; j < action.getCount(); j++) scope.fork(() => action.calcPart(input, j));
}
<span class="hljs-comment" style="color:rgb(153,153,136);font-style:italic">// !! Undefined behavior !!</span>
<span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">for</span> (var action : actions) {
var scope = scopes.get(action);
scope.join();
action.aggregateParts();
scope.close();
}
}
</code></pre>
<p style="margin:0px 0px 1.2em!important">Some implementations of <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">Collection</code> that will always fail, some will always succeed, and some implementations (like <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">HashSet</code>) may be non-deterministic.<br>For the uninformed this method makes sense, for each <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">PartitiableAction</code> I create some kind of a new “<code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">Executor</code>“ that everyone is talking about, if one of the parts fails, the whole calculation of this specific <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">PartitiableAction</code> will stop running, and I am waiting for everything to end.</p>
<hr>
<p style="margin:0px 0px 1.2em!important">I can write a PoC compiler plugin such that classes with <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">@StrongTwR</code> annotation can only be assigned inside TwR (unless they are also the return value) (I will probably do it tomorrow and send a link to it in a follow up mail if people are interested)</p>
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aXY+PC9kaXY+PC9kaXY+" style="height:0;width:0;max-height:0;max-width:0;overflow:hidden;font-size:0em;padding:0;margin:0"></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Aug 4, 2022 at 11:51 AM Andrew Haley <<a href="mailto:aph-open@littlepinkcloud.com">aph-open@littlepinkcloud.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On 7/29/22 21:37, Ron Pressler wrote:<br>
> Yes, we are thinking about a "strong” TwR, but we’re busy with so many things so it might take a while. Until then, we might introduce a weaker, or less trustworthy version of ExtentLocals that uses the existing TwR and wouldn’t be used for critical things, but we think that it’s best to start incubation with just the lambda API and then see what problems are most common/annoying and how we can best address them.<br>
<br>
One of the worst problems with using "weak" TWR for extent locals is that<br>
ensuring the invariants with respect to structured concurrency is hard.<br>
You end up with complex consistency checks that must be checked at runtime,<br>
and are hard to test.<br>
<br>
-- <br>
Andrew Haley (he/him)<br>
Java Platform Lead Engineer<br>
Red Hat UK Ltd. <<a href="https://www.redhat.com" rel="noreferrer" target="_blank">https://www.redhat.com</a>><br>
<a href="https://keybase.io/andrewhaley" rel="noreferrer" target="_blank">https://keybase.io/andrewhaley</a><br>
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671<br>
</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr">Holo The Wise Wolf Of Yoitsu</div></div>