<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Hi all,<br data-mce-bogus="1"></div><div>I've spent some time to try to improve the API given the constraints,</div><div>- an API instead of a language feature,<br></div><div>- distangle the fields initialized lazily from the ones initialized in the <clinit>,<br></div><div>- the initialization code is made thread safe and executed exactly once,<br data-mce-bogus="1"></div><div>- as fast as a static final constant when c2 optimize the code,</div><div>- condenser friendly,<br data-mce-bogus="1"></div><div>- can evolve to a langage feature in the future.<br></div><div><br data-mce-bogus="1"></div><div>I've re-used the idea of John of having one method able to initialize all the computed/autonomous fields, but it uses strings instead of ints because ints are not very user friendly :)<br data-mce-bogus="1"></div><div>I have one central object per class, i've called it FieldInit but I'm sure there is a better name. It it only able to initialize the field of the lookup class taken as parameter (I hope the current class).<br data-mce-bogus="1"></div><div>It has one method get(fieldName) that takes a field name as parameter and return the corresponding value lazily initialized. There are also overloads for all primitive types but it's more for convenience than anything else. The semantics for the initialization is the same as with a computed constant (I hope I get this right).</div><div><br data-mce-bogus="1"></div><div><div style="background-color: #ffffff; color: #080808;" data-mce-style="background-color: #ffffff; color: #080808;"><pre style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;" data-mce-style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;"><span style="color: #0033b3;" data-mce-style="color: #0033b3;">public class </span><span style="color: #000000;" data-mce-style="color: #000000;">Main </span>{<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">private static final </span><span style="color: #000000;" data-mce-style="color: #000000;">FieldInit </span><span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">FIELD_INIT </span>= <span style="color: #000000;" data-mce-style="color: #000000;">FieldInit</span>.<span style="font-style: italic;" data-mce-style="font-style: italic;">ofStatic</span>(<span style="color: #000000;" data-mce-style="color: #000000;">MethodHandles</span>.<span style="font-style: italic;" data-mce-style="font-style: italic;">lookup</span>());<br><br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">private static </span><span style="color: #000000;" data-mce-style="color: #000000;">Object </span><span style="color: #00627a;" data-mce-style="color: #00627a;">$staticFieldInit$</span>(<span style="color: #000000;" data-mce-style="color: #000000;">String </span>fieldName) {<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">return switch </span>(fieldName) {<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">case </span><span style="color: #067d17;" data-mce-style="color: #067d17;">"X" </span>-> <span style="color: #1750eb;" data-mce-style="color: #1750eb;">42</span>;<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">case </span><span style="color: #067d17;" data-mce-style="color: #067d17;">"HELLO" </span>-> <span style="color: #067d17;" data-mce-style="color: #067d17;">"hello field init !"</span>;<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">default </span>-> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">throw new </span>AssertionError(<span style="color: #067d17;" data-mce-style="color: #067d17;">"unknown " </span>+ fieldName);<br> };<br> }<br><br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">private static int </span><span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">X</span>;<br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">private static </span><span style="color: #000000;" data-mce-style="color: #000000;">String </span><span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">HELLO</span>;<br><br> <span style="color: #0033b3;" data-mce-style="color: #0033b3;">public static void </span><span style="color: #00627a;" data-mce-style="color: #00627a;">main</span>(<span style="color: #000000;" data-mce-style="color: #000000;">String</span>[] args) {<br> <span style="color: #000000;" data-mce-style="color: #000000;">System</span>.<span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">out</span>.println(<span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">FIELD_INIT</span>.getInt(<span style="color: #067d17;" data-mce-style="color: #067d17;">"X"</span>)); // 42<br> <span style="color: #000000;" data-mce-style="color: #000000;">System</span>.<span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">out</span>.println(<span style="color: #871094; font-style: italic;" data-mce-style="color: #871094; font-style: italic;">FIELD_INIT</span>.<<span style="color: #000000;" data-mce-style="color: #000000;">String</span>>get(<span style="color: #067d17;" data-mce-style="color: #067d17;">"HELLO"</span>)); // hello field init<br> }<br>}<br><br>Major issues with that API,<br>- it's string based so a renaming of one of the computed/autonomous field will make the corresponding FieldInit.get() to fail at runtime with a NoSuchFieldError,<br>- it's not typesafe, a user can ask for the value of an int field as a String, it will fail at runtime with a ClassCastException,<br>- if a code that directly access to a computed/autonomous field instead of using FieldInit.get() may see either the default value or the intialized value (don't do that),<br>- the implementation put a lot more pressure to the JIT so the time to steady state may be delayed compared to a solution without computed/autonomous fields.<br><br>The implementation is available here:<br> https://github.com/forax/computed-constant/tree/master/field-init/src/main/java/com/github/forax/concurrent/constant<br><br><br>The time to access to static final constant and to access to static constant through FieldInit.get() is identical once c2 JIT the code.<br></pre></div></div><div><span style="font-family: courier new, courier, monaco, monospace, sans-serif;" data-mce-style="font-family: courier new, courier, monaco, monospace, sans-serif;">Benchmark Mode Cnt Score Error Units</span><br><span style="font-family: courier new, courier, monaco, monospace, sans-serif;" data-mce-style="font-family: courier new, courier, monaco, monospace, sans-serif;">Benchmarks.static_constant_get_42 avgt 5 0.316 ± 0.001 ns/op</span><br><span style="font-family: courier new, courier, monaco, monospace, sans-serif;" data-mce-style="font-family: courier new, courier, monaco, monospace, sans-serif;">Benchmarks.static_constant_get_null avgt 5 0.316 ± 0.001 ns/op</span><br><span style="font-family: courier new, courier, monaco, monospace, sans-serif;" data-mce-style="font-family: courier new, courier, monaco, monospace, sans-serif;">Benchmarks.static_field_init_get_42 avgt 5 0.315 ± 0.001 ns/op</span><br><span style="font-family: courier new, courier, monaco, monospace, sans-serif;" data-mce-style="font-family: courier new, courier, monaco, monospace, sans-serif;">Benchmarks.static_field_init_get_null avgt 5 0.316 ± 0.001 ns/op</span><br></div><div><br data-mce-bogus="1"></div><div><pre style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;" data-mce-style="font-family: 'JetBrains Mono',monospace; font-size: 9.8pt;">I've not implemented the initialization of the instance field, mostly because I want feedback on this proposal before going further and unlike with a computed constant, there is a problem to make the difference between an uninitialized value and a default value of an instance field.</pre></div><div>regards,</div><div>Rémi<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>PS: There is also possible implementation using a template processor especially if it implements TemplatedString.Processor.Linkage. Something like FieldInitProcessor."X". Sadly, FieldInitProcessor.<Integer>"X" is not legal, there is no easy way to specify a return type.</div><div><br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Per-Ake Minborg" <per-ake.minborg@oracle.com><br><b>To: </b>"leyden-dev" <leyden-dev@openjdk.org><br><b>Sent: </b>Thursday, July 27, 2023 5:52:46 PM<br><b>Subject: </b>Draft JEP Announcement: "Computed Constants"<br></blockquote></div><div><style style="display:none;"> P {margin-top:0;margin-bottom:0;} </style></div><div data-marker="__QUOTED_TEXT__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">
<span class="x_elementToProof" style="font-size: 12pt; margin: 0px; background-color: rgb(255, 255, 255);"><span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Hi
all,</span></span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">
<div class="x_elementToProof" style="font-size: 12pt; margin: 0px; background-color: rgb(255, 255, 255);">
<br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> Maurizio and I have drafted a JEP for computed constants, which are</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> immutable value holders that are initialized at most once. They offer</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> the performance and safety benefits of final fields while offering</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> greater flexibility as to the timing of initialization. In the</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> context of Leyden, they could be one basis for shifting computation</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> both forward and backward in time.</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
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<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> The draft is here:<span class="x_ContentPasted0 ContentPasted0" style="margin:0px"> </span></span><a href="https://openjdk.org/jeps/8312611" target="_blank" rel="noopener noreferrer" class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; background-color: rgb(255, 255, 255);">https://openjdk.org/jeps/8312611</a><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
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<br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> Now that the Leyden repo is open, I’ll publish the prototype code to a</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> new branch there shortly.</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
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<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> Comments are welcome!</span><br class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">
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<div class="x_elementToProof" style="font-size: 12pt; margin: 0px; background-color: rgb(255, 255, 255);">
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<span class="x_ContentPasted0 ContentPasted0" style="font-size: 14.6667px; margin: 0px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"> Best, Per</span></div>
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