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<div class="elementToProof"><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">Hi R¨¦mi,</span></div>
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</span></div>
<div class="elementToProof"><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">For instance, stateless is neither recessive nor dominant, since the composition of
two stateless operations is only ever stateless if they both are greedy as well:
</span><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"><a href="https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/stream/Gatherers.java#L588" id="LPlnk413539">https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/stream/Gatherers.java#L588</a></span></div>
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So even if making it represented as ints (more like Spliterator, rather than Collector) makes things faster, it's still both work to track, propagate, and also becomes a side-channel that needs to remain in sync with the actual implementation of the logic.</div>
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One could argue that logic such as: someCollection.stream().map(¡).count() is a performance bug/inefficiency in an of itself as it would be faster to do someCollection.size().</div>
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Cheers,<br>
¡Ì</div>
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<b><br>
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<b>Viktor Klang</b></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Software Architect, Java Platform Group<br>
Oracle</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> forax@univ-mlv.fr <forax@univ-mlv.fr><br>
<b>Sent:</b> Saturday, 20 January 2024 17:40<br>
<b>To:</b> Viktor Klang <viktor.klang@oracle.com><br>
<b>Cc:</b> core-libs-dev <core-libs-dev@openjdk.java.net>; Paul Sandoz <psandoz@openjdk.java.net><br>
<b>Subject:</b> [External] : Re: Gatherer: spliterator characteristics are not propagated</font>
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<b>From: </b>"Viktor Klang" <viktor.klang@oracle.com><br>
<b>To: </b>"Remi Forax" <forax@univ-mlv.fr><br>
<b>Cc: </b>"core-libs-dev" <core-libs-dev@openjdk.java.net>, "Paul Sandoz" <psandoz@openjdk.java.net><br>
<b>Sent: </b>Thursday, January 18, 2024 5:14:38 PM<br>
<b>Subject: </b>Re: Gatherer: spliterator characteristics are not propagated<br>
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And for A.andThen(B), A.flags & B.flags should work, the stream is sorted if both gatherers keep it sorted.</div>
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That is unfortunately not the case. That would presume that you can implement the composition such that it can preserve all the common flags. Some flags could be "dominant" and some "recessive" to use genetics nomenclature.</div>
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<div>Some flags of the stream pipeline are "recessive", mainly SHORT_CIRCUIT, but not the characteristics of the Gatherer which can have the corresponding "dominant" flag, GREEDY, in this case.</div>
<div>And the same for sequential, the flag should be PARALELIZABLE and not SEQUENTIAL.</div>
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<div>The idea is that the Gatherer characteristics can have the same bit set at the same position as the stream op flags (as defined by StreamOpFlag).<br>
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<div>So KEEP_DISTINCT is in position 0, KEEP_SORTED in in position 2 and KEEP_SIZED is in position 3.</div>
<div>For GREEDY, we use the same position as SHORT_CIRCUIT and we will flip the bit (using XOR) when we want to extract the stream op flags from the characteristics</div>
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<div>All the factory methods call the generic of() with a combination of PARALELIZABLE and STATELESS and the user can adds the characteristics GREEDY, KEEP_DISTINCT, KEEP_SORTED and KEEP_SIZED (otherwise an exception should be raised).<br>
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<div>In StreamOpFlag, there are two unused positions (14 and 15), that's perfect for our two new states PARALELIZABLE and STATELESS, so no problem here (technically we can also reuse positions of the Spliterator characteristic given that those flags are masked
before being sent to the GathererOp super constructor).</div>
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<div>The way to transform a Gatherer characteristics op to a stream flags op is to flip the bits corresponding to SHORT_CIRCUIT, add the highter bit of all flags but SHORT-CIRCUIT (because stream op flags are encoded using 2 bits) and mask to only retain SHORT_CIRCUIT,
KEEP_DISTINCT, KEEP_SORTED and KEEP_SIZED.<br>
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<pre data-mce-style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;" style="font-family:'JetBrains Mono',monospace; font-size:9.8pt"><span data-mce-style="color: #0033b3;" style="color:#0033b3">public static int </span><span data-mce-style="color: #00627a;" style="color:#00627a">toOpFlags</span>(<span data-mce-style="color: #0033b3;" style="color:#0033b3">int </span><span data-mce-style="color: #000000;" style="color:#000000">characteristics</span>) {<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span>((<span data-mce-style="color: #000000;" style="color:#000000">characteristics </span>^ <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_MASK</span>) | <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">HIGHER_BITS</span>) & <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STREAM_OP_MASK</span>;<br>}</pre>
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<div>see below for a full script.<br data-mce-bogus="1">
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I suppose that if those flags already exist, it's because they have a purpose and i do not understand how it can make the other operations slower.</div>
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Extra invocations, extra storage, and extra composition overhead is not free. Since Stream is one-shot you need to include the construction cost with the execution cost. For something like an empty Stream construction cost scan be 90+% of the total costs.</div>
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<div>If you create a Gatherer, the characteristics is a constant (so the validity check is removed, it's just a mask and a test) so the result of calling toOpFlags() is a constant too.<br data-mce-bogus="1">
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<div>If the factory method is not inlined, the cost is 3 bitwise operations which is I believe faster than the "instanceof Greedy" used in the current code.</div>
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Cheers,<br>
¡Ì</div>
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<div>regards,<br>
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<div>R¨¦mi<br data-mce-bogus="1">
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<pre data-mce-style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;" style="font-family:'JetBrains Mono',monospace; font-size:9.8pt"><span data-mce-style="color: #0033b3;" style="color:#0033b3">public class </span><span data-mce-style="color: #000000;" style="color:#000000">GathererFlag </span>{<br> <span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic">// cut and paste from StreamOpFlag<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> /**<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> * The bit pattern for setting/injecting a flag.<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> */<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> </span><span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span>= <span data-mce-style="color: #1750eb;" style="color:#1750eb">0b01</span>;<br><br> <span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic">/**<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> * The bit pattern for clearing a flag.<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> */<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> </span><span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">CLEAR_BITS </span>= <span data-mce-style="color: #1750eb;" style="color:#1750eb">0b10</span>;<br><br> <span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic">/**<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> * The bit pattern for preserving a flag.<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> */<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> </span><span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PRESERVE_BITS </span>= <span data-mce-style="color: #1750eb;" style="color:#1750eb">0b11</span>;<br><br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static int </span><span data-mce-style="color: #00627a;" style="color:#00627a">position</span>(<span data-mce-style="color: #0033b3;" style="color:#0033b3">int </span><span data-mce-style="color: #000000;" style="color:#000000">opFlagSet</span>) {<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #000000;" style="color:#000000">Integer</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">numberOfTrailingZeros</span>(<span data-mce-style="color: #000000;" style="color:#000000">opFlagSet</span>) >> <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>;<br> }<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">DISTINCT_POSITION </span>= <span data-mce-style="font-style: italic;" style="font-style:italic">position</span>(<span data-mce-style="color: #000000;" style="color:#000000">StreamOpFlag</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">IS_DISTINCT</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SORTED_POSITION </span>= <span data-mce-style="font-style: italic;" style="font-style:italic">position</span>(<span data-mce-style="color: #000000;" style="color:#000000">StreamOpFlag</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">IS_SORTED</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SIZED_POSITION </span>= <span data-mce-style="font-style: italic;" style="font-style:italic">position</span>(<span data-mce-style="color: #000000;" style="color:#000000">StreamOpFlag</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">IS_SIZED</span>);<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_POSITION </span>= <span data-mce-style="font-style: italic;" style="font-style:italic">position</span>(<span data-mce-style="color: #000000;" style="color:#000000">StreamOpFlag</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">IS_SHORT_CIRCUIT</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS_POSITION </span>= <span data-mce-style="color: #1750eb;" style="color:#1750eb">14</span>;<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE_POSITION </span>= <span data-mce-style="color: #1750eb;" style="color:#1750eb">15</span>;<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">DISTINCT_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SORTED_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SIZED_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_MASK </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SET_BITS </span><< (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_POSITION </span><< <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>);<br><br> <span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic">// no GREEDY here<br></span><span data-mce-style="color: #8c8c8c; font-style: italic;" style="color:#8c8c8c; font-style:italic"> </span><span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">HIGHER_BITS </span>= (<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>) << <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>;<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">private static final int </span><span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STREAM_OP_MASK </span>=<br> ((<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>) << <span data-mce-style="color: #1750eb;" style="color:#1750eb">1</span>) |<br> <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>;<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static </span><span data-mce-style="color: #000000;" style="color:#000000">String </span><span data-mce-style="color: #00627a;" style="color:#00627a">toString</span>(<span data-mce-style="color: #0033b3;" style="color:#0033b3">int </span><span data-mce-style="color: #000000;" style="color:#000000">characteristics</span>) {<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #000000;" style="color:#000000">Stream</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">of</span>(<span data-mce-style="color: #000000;" style="color:#000000">characteristics</span>)<br> .<<span data-mce-style="color: #000000;" style="color:#000000">String</span>>mapMulti((<span data-mce-style="color: #000000;" style="color:#000000">f</span>, <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>) -> {<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"PARELLIZABLE"</span>);<br> }<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"STATELESS"</span>);<br> }<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"GREEDY"</span>);<br> }<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"KEEP_DISTINCT"</span>);<br> }<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"KEEP_SORTED"</span>);<br> }<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>((<span data-mce-style="color: #000000;" style="color:#000000">f </span>& <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>) == <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>) {<br> <span data-mce-style="color: #000000;" style="color:#000000">consumer</span>.accept(<span data-mce-style="color: #067d17;" style="color:#067d17">"KEEP_SIZED"</span>);<br> }<br> })<br> .collect(<span data-mce-style="color: #000000;" style="color:#000000">Collectors</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">joining</span>(<span data-mce-style="color: #067d17;" style="color:#067d17">", "</span>));<br> }<br><br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">public static int </span><span data-mce-style="color: #00627a;" style="color:#00627a">toOpFlags</span>(<span data-mce-style="color: #0033b3;" style="color:#0033b3">int </span><span data-mce-style="color: #000000;" style="color:#000000">characteristics</span>) {<br> <span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span>((<span data-mce-style="color: #000000;" style="color:#000000">characteristics </span>^ <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">SHORT_CIRCUIT_MASK</span>) | <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">HIGHER_BITS</span>) & <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STREAM_OP_MASK</span>;<br>}<br><br><span data-mce-style="color: #0033b3;" style="color:#0033b3">public static </span><span data-mce-style="color: #000000;" style="color:#000000">String </span><span data-mce-style="color: #00627a;" style="color:#00627a">toOpFlagsString</span>(<span data-mce-style="color: #0033b3;" style="color:#0033b3">int </span><span data-mce-style="color: #000000;" style="color:#000000">opFlags</span>) {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #000000;" style="color:#000000">Arrays</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">stream</span>(<span data-mce-style="color: #000000;" style="color:#000000">StreamOpFlag</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">values</span>())<br>.map(<span data-mce-style="color: #000000;" style="color:#000000">op </span>-> {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>(<span data-mce-style="color: #000000;" style="color:#000000">op</span>.isPreserved(<span data-mce-style="color: #851691;" style="color:#851691">opFlags</span>)) {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #067d17;" style="color:#067d17">"preserved " </span>+ <span data-mce-style="color: #000000;" style="color:#000000">op</span>;<br>}<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>(<span data-mce-style="color: #000000;" style="color:#000000">op</span>.isCleared(<span data-mce-style="color: #851691;" style="color:#851691">opFlags</span>)) {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #067d17;" style="color:#067d17">"cleared " </span>+ <span data-mce-style="color: #000000;" style="color:#000000">op</span>;<br>}<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">if </span>(<span data-mce-style="color: #000000;" style="color:#000000">op</span>.isKnown(<span data-mce-style="color: #851691;" style="color:#851691">opFlags</span>)) {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #067d17;" style="color:#067d17">"set " </span>+ <span data-mce-style="color: #000000;" style="color:#000000">op</span>;<br>}<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">return </span><span data-mce-style="color: #067d17;" style="color:#067d17">"?? " </span>+ <span data-mce-style="color: #000000;" style="color:#000000">op</span>;<br>})<br>.collect(<span data-mce-style="color: #000000;" style="color:#000000">Collectors</span>.<span data-mce-style="font-style: italic;" style="font-style:italic">joining</span>(<span data-mce-style="color: #067d17;" style="color:#067d17">", "</span>));<br>}<br><br><span data-mce-style="color: #0033b3;" style="color:#0033b3">void </span><span data-mce-style="color: #00627a;" style="color:#00627a">main</span>() {<br><span data-mce-style="color: #0033b3;" style="color:#0033b3">var </span><span data-mce-style="color: #000000;" style="color:#000000">characteristics </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">PARELLIZABLE </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">GREEDY </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SORTED </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>;<br><span data-mce-style="color: #000000;" style="color:#000000">System</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">out</span>.println(<span data-mce-style="font-style: italic;" style="font-style:italic">toOpFlagsString</span>(<span data-mce-style="font-style: italic;" style="font-style:italic">toOpFlags</span>(<span data-mce-style="color: #000000;" style="color:#000000">characteristics</span>)));<br><br><span data-mce-style="color: #0033b3;" style="color:#0033b3">var </span><span data-mce-style="color: #000000;" style="color:#000000">characteristics2 </span>= <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">STATELESS </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_DISTINCT </span>| <span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">KEEP_SIZED</span>;<br><span data-mce-style="color: #000000;" style="color:#000000">System</span>.<span data-mce-style="color: #871094; font-style: italic;" style="color:#871094; font-style:italic">out</span>.println(<span data-mce-style="font-style: italic;" style="font-style:italic">toOpFlagsString</span>(<span data-mce-style="font-style: italic;" style="font-style:italic">toOpFlags</span>(<span data-mce-style="color: #000000;" style="color:#000000">characteristics2</span>)));<br>}<br>}</pre>
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<b>Viktor Klang</b></div>
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Software Architect, Java Platform Group<br>
Oracle</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><span data-mce-style="font-family: Calibri, sans-serif; font-size: 11pt; color: #000000;" style="font-family:Calibri,sans-serif; font-size:11pt; color:#000000"><b>From:</b> forax@univ-mlv.fr <forax@univ-mlv.fr><br>
<b>Sent:</b> Thursday, 18 January 2024 16:17<br>
<b>To:</b> Viktor Klang <viktor.klang@oracle.com><br>
<b>Cc:</b> core-libs-dev <core-libs-dev@openjdk.java.net>; Paul Sandoz <psandoz@openjdk.java.net><br>
<b>Subject:</b> [External] : Re: Gatherer: spliterator characteristics are not propagated</span>
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<span data-mce-style="font-family: Helvetica, Arial, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Helvetica,Arial,sans-serif; font-size:12pt; color:#000000"><b>From:
</b>"Viktor Klang" <viktor.klang@oracle.com><br>
<b>To: </b>"Remi Forax" <forax@univ-mlv.fr><br>
<b>Cc: </b>"core-libs-dev" <core-libs-dev@openjdk.java.net>, "Paul Sandoz" <psandoz@openjdk.java.net><br>
<b>Sent: </b>Thursday, January 18, 2024 3:36:07 PM<br>
<b>Subject: </b>Re: Gatherer: spliterator characteristics are not propagated<br>
</span></blockquote>
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I suspect that it is a rather slippery slope, once KEEP-flags are added, then others will want to be able to have INJECT-flags, and then people might have different opinions w.r.t. the default should be to clear all flags etc.</div>
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<br>
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And that's even before one looks at the composition-part of it, what are the flags for A.andThen(B)? (then extrapolate to N compositions and the available set of flags always approaches 0)</div>
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<br>
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I spent quite a bit of time on this and in the end tracking all this info, and making sure that the flags of implementations correspond to the actual behavior, just ended up costing performance for most streams and introduced an extra dimension to creation
and maintenance which I had a hard time justifying.</div>
</blockquote>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">It can be a slippery slope if we were designing from the ground up but the
stream implementation already exists and SORTED, DISTINCT and SIZED are the flags that are already tracked by the current implementation.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">Currently only SHORT_CIRCUIT is set (if not greedy),</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">see
<a href="https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/stream/GathererOp.java*L209__;Iw!!ACWV5N9M2RV99hQ!PhMxqlDzLWPRuwYc7ECRKNPVs0BtnoE-RdT-Jdkng7S-iFuERAHYcWvJ-OMKGLrkPdSrUl3xj1R9ypyeqeWI$" id="OWA1a26d136-987c-a5b2-e72e-dde19d919aa9" class="x_OWAAutoLink" target="_blank" rel="noopener" data-mce-href="https://urldefense.com/v3/__https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/stream/GathererOp.java*L209__;Iw!!ACWV5N9M2RV99hQ!PhMxqlDzLWPRuwYc7ECRKNPVs0BtnoE-RdT-Jdkng7S-iFuERAHYcWvJ-OMKGLrkPdSrUl3xj1R9ypyeqeWI$">
https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/util/stream/GathererOp.java#L209</a></span><br data-mce-bogus="1">
</div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">And for A.andThen(B), A.flags & B.flags should work, the stream is sorted if
both gatherers keep it sorted.</span></div>
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</span></div>
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<br>
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Making specific, rare, combinations of operations faster at the expense of making 99% of all others slower is a hard pill for most to swallow.</div>
</blockquote>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">I suppose that if those flags already exist, it's because they have a purpose
and i do not understand how it can make the other operations slower.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
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<br>
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<br>
</div>
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Cheers,<br>
¡Ì</div>
</div>
</blockquote>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">regards,</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">R¨¦mi</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
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<div id="x_x_Signature">
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<br>
</div>
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<b><br>
</b></div>
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<b>Viktor Klang</b></div>
<div data-mce-style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:#000000">
Software Architect, Java Platform Group<br>
Oracle</div>
</div>
<hr data-mce-style="display: inline-block; width: 98%;" style="display:inline-block; width:98%">
<div id="x_x_divRplyFwdMsg" dir="ltr"><span data-mce-style="font-family: Calibri, sans-serif; font-size: 11pt; color: #000000;" style="font-family:Calibri,sans-serif; font-size:11pt; color:#000000"><b>From:</b> forax@univ-mlv.fr <forax@univ-mlv.fr><br>
<b>Sent:</b> Thursday, 18 January 2024 10:28<br>
<b>To:</b> Viktor Klang <viktor.klang@oracle.com><br>
<b>Cc:</b> core-libs-dev <core-libs-dev@openjdk.java.net>; Paul Sandoz <psandoz@openjdk.java.net><br>
<b>Subject:</b> [External] : Re: Gatherer: spliterator characteristics are not propagated</span>
<div> </div>
</div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<hr>
<blockquote data-mce-style="margin-left: 5px; padding-left: 5px; border-left: 2px solid #1010ff;" style="margin-left:5px; padding-left:5px; border-left:2px solid #1010ff">
<span data-mce-style="font-family: Helvetica, Arial, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Helvetica,Arial,sans-serif; font-size:12pt; color:#000000"><b>From:
</b>"Viktor Klang" <viktor.klang@oracle.com><br>
<b>To: </b>"Remi Forax" <forax@univ-mlv.fr>, "core-libs-dev" <core-libs-dev@openjdk.java.net><br>
<b>Sent: </b>Wednesday, January 17, 2024 8:48:07 PM<br>
<b>Subject: </b>Re: Gatherer: spliterator characteristics are not propagated<br>
</span></blockquote>
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<div data-mce-style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif; font-size:12pt; color:#000000">
Hi R¨¦mi,</div>
<div data-mce-style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif; font-size:12pt; color:#000000">
<br>
</div>
<div><span data-mce-style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif; font-size:12pt; color:#000000">You
can find some of my benches here: <a href="https://urldefense.com/v3/__https://github.com/openjdk/jdk/tree/master/test/micro/org/openjdk/bench/java/util/stream/ops/ref__;!!ACWV5N9M2RV99hQ!JJy6F9NoL6wKZQK5158up_fTRvH8X7F6JK8T7Euuf8vzbSQbr23eWa9S_yb61ksONVrLrdesCF_au5zyje2l$" id="OWA080e8c5b-35bc-94d6-7d9f-60a18ae54e23" class="x_OWAAutoLink" target="_blank" rel="noopener" data-mce-href="https://urldefense.com/v3/__https://github.com/openjdk/jdk/tree/master/test/micro/org/openjdk/bench/java/util/stream/ops/ref__;!!ACWV5N9M2RV99hQ!JJy6F9NoL6wKZQK5158up_fTRvH8X7F6JK8T7Euuf8vzbSQbr23eWa9S_yb61ksONVrLrdesCF_au5zyje2l$">
https://github.com/openjdk/jdk/tree/master/test/micro/org/openjdk/bench/java/util/stream/ops/ref</a></span><br data-mce-bogus="1">
</div>
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<br>
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<div data-mce-style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:Aptos,Aptos_EmbeddedFont,Aptos_MSFontService,Calibri,Helvetica,sans-serif; font-size:12pt; color:#000000">
Initially I had Characteristics such as ORDERED etc on Gatherer but it just didn't end up worth it when looking at the bench results over a wide array of stream sizes and number of operations.</div>
</blockquote>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">I think there are 3 gatherer characteristics that make sense: KEEP_SORTED,
KEEP_DISTINCT and KEEP_SIZED,</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">all of them say that if the stream was sorted/distinct/sized then the stream
returned by a call to gather() is still sorted (with the same comparator), distinct or sized.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">As examples, map() is KEEP_SIZED, filter() is KEEP_SORTED | KEEP_DISTINCT and
windowFixed is KEEP_DISTINCT.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">[CC Paul, so he can correct me if i'm saying something stupid]</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">Now for the benchmarks, it depends what you want to measure, benchmarking streams
is tricky. This is what i know about benchmarking streams.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">First, the JIT has two ways to profile types at runtime,</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">Either a method takes a function as parameter</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> void map(Function function) {</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> function.apply(...)</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> }</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">and when map is called with a subtype of Function, the JIT will propagate the
exact type when map is inlined,</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">Or a method use a field</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> class Op {</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> Function function;</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> void map() {</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> function.apply(...)</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> }</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"> }</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">in that case, the VM records the profile of function.apply() and if there are
more than two different profiles, the VM declare profile poluttion and do not try to optimize.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">The Stream implementation tries very hard to use only parameters instead of
fields, that's why it does not use classical Iterator that are pull iterator (a filter iterator requires a field) but a Spliterator which is a push iterator, the element is sent as parameter of the consumer.That's also why collect does not use the builder
pattern (that accumulate values in fields) but a Collector that publish the functions to be called as parameter.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">Obvisously, this is more complex than that, a Collector stores the functions
in fields so it should not work well but the implementation uses a record that plays well with escape analysis. Escape analysis see the fields of an instance as parameters so the functions of a Collector are correctly propagated (if the escape analysis works).
And lambdas are using invokedynamic, and the VM tries really hard to inline invokedynamic, so lambdas (that captures value or not) are routinely fully inlined with the intermediate operation of a stream.</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000"><br>
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<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">In your tests, i've not seen comparaisons between an existing method like map()
or filter() followed by a sorted()/distinct()/count()/toList(), i.e. operations where the characteristics KEEP_* have an impact and their equivalent using a Gatherer.</span></div>
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Cheers,<br>
¡Ì</div>
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<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">regards,</span></div>
<div><span data-mce-style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000;" style="font-family:arial,helvetica,sans-serif; font-size:12pt; color:#000000">R¨¦mi</span></div>
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<b><br>
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<b>Viktor Klang</b></div>
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Software Architect, Java Platform Group<br>
Oracle</div>
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<div id="x_x_x_divRplyFwdMsg" dir="ltr"><span data-mce-style="font-family: Calibri, sans-serif; font-size: 11pt; color: #000000;" style="font-family:Calibri,sans-serif; font-size:11pt; color:#000000"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org>
on behalf of Remi Forax <forax@univ-mlv.fr><br>
<b>Sent:</b> Wednesday, 17 January 2024 16:48<br>
<b>To:</b> core-libs-dev <core-libs-dev@openjdk.java.net><br>
<b>Subject:</b> Gatherer: spliterator characteristics are not propagated</span>
<div> </div>
</div>
<div><span data-mce-style="font-family: Helvetica, Arial, sans-serif; font-size: 11pt; color: #000000;" style="font-family:Helvetica,Arial,sans-serif; font-size:11pt; color:#000000">While doing some benchmarking of the Gatherer API, i've found that the characteristics
of the spliterator was not propagated by the method Stream.gather() making the stream slower than it should.<br>
<br>
As an example, there is no way when reimplementing map() using a Gatherer to say that this intermediate operation keep the size, which is important if the terminal operation is toList() because if the size is known, toList() will presize the List and avoid
the creation of an intermediary ArrayList.<br>
<br>
See <a href="https://urldefense.com/v3/__https://github.com/forax/we_are_all_to_gather/blob/master/src/main/java/com/gihtub/forax/wearealltogather/bench/MapGathererBenchmark.java__;!!ACWV5N9M2RV99hQ!JJy6F9NoL6wKZQK5158up_fTRvH8X7F6JK8T7Euuf8vzbSQbr23eWa9S_yb61ksONVrLrdesCF_auzwTY8aB$" id="OWA4df2922d-e2cf-d3f2-96d5-6a217e6e8f51" class="x_OWAAutoLink" target="_blank" rel="noopener" data-mce-href="https://urldefense.com/v3/__https://github.com/forax/we_are_all_to_gather/blob/master/src/main/java/com/gihtub/forax/wearealltogather/bench/MapGathererBenchmark.java__;!!ACWV5N9M2RV99hQ!JJy6F9NoL6wKZQK5158up_fTRvH8X7F6JK8T7Euuf8vzbSQbr23eWa9S_yb61ksONVrLrdesCF_auzwTY8aB$">
https://github.com/forax/we_are_all_to_gather/blob/master/src/main/java/com/gihtub/forax/wearealltogather/bench/MapGathererBenchmark.java</a><br>
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I think that adding a way to propagate the spliterator characteristics through a Gatherer would greatly improve the performance of commons streams (at least all the ones that end with a call to toList).<br>
<br>
I have some idea of how to do that, but I prefer first to hear if i've overlook something and if improving the performance is something worth changing the API.<br>
<br>
regards,<br>
R¨¦mi</span></div>
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