<div dir="ltr"><div dir="ltr"><div class="gmail_default"><font size="4">Hi Christoph,</font><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jan 1, 2021 at 4:18 PM Thiede, Christoph <<a href="mailto:Christoph.Thiede@student.hpi.uni-potsdam.de">Christoph.Thiede@student.hpi.uni-potsdam.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<p>Hi Eliot,</p>
<p><br>
</p>
<p>once again I am very pleasantly surprised by your professional and detailed answer which was a joy to read!</p>
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<div><font size="3" color="black"><span style="font-size:12pt"><a href="http://www.hpi.de/" rel="noopener noreferrer" id="gmail-m_-2979770936573098614LPNoLP" target="_blank"><font size="2"><span id="gmail-m_-2979770936573098614LPlnk909538"><font color="#757B80"></font></span></font></a></span></font></div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody">> <span style="font-size:12pt">'Nuff said</span>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody">No further questions. This was very interesting!</div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody">It also gives me a possible explanation for why one cannot execute a context subinstance without any problems. That's because the marriage between stack frame and context objects is hard-coded based on the Context
class (specialObjects at: 11), isn't it?</div></div></div></div></div></div></div></div></blockquote><div><font size="4"><br></font></div><div class="gmail_default"><font size="4">Indeed. One may be able to go the other way, create a stack of contexts whose class is different. These should retain their class because the associated stack frames will be married to them. But going the other way is not supported.</font></div><div class="gmail_default"><font size="4"></font></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif" dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div id="gmail-m_-2979770936573098614Signature"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div name="divtagdefaultwrapper"><div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody"><span style="font-size:12pt">> </span><span style="font-size:12pt">But beware, because if one was debugging the debugger one mustn't confuse a PrimFailToken created in the simulation for a PrimFailToken created by the simulation.</span><br></div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span>Hm, aren't we already in a very similar situation? I had planned to write a separate message for this issue, but here is my case:</span></div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span>
<div>{Context primitiveFailTokenFor: nil} at: 1. "{an Object . nil}"</div>
<div>Context runSimulated: [{Context primitiveFailTokenFor: nil} at: 1]. "⚡ Error: subscript is out of bounds: 1"</div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span>Now one could argue that this is not a very likely situation to occur ever in "production", but the same could be said for a hypothetical #<span>isPrimFailToken selector, and above all, it precludes an ideal,
i.e. completely transparent simulation machinery ...<span></span></span></span></div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span><span>So I would like to suggest to find a different solution for this problem anyway, provided that you support this idea in general.</span></span></div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span><span>An alternative I could imagine would be the SetElement pattern from Collections which is completely transparent. But this would probably be too expensive for simulation purposes (because we would need
to instantiate one object per simulated primitive call), right?</span></span></div></div></div></div></div></div></div></div></blockquote><div><font size="4"><br></font></div><div class="gmail_default"><font size="4">Not sure. If instantiation can be deferred until failure then things should be OK.</font></div><div class="gmail_default"><font size="4"></font></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif" dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div id="gmail-m_-2979770936573098614Signature"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div name="divtagdefaultwrapper"><div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span><span>Why not encode a failing primitive via a changed control flow? Couldn't we pass an additional failBlock argument to #<span>doPrimitive:method:receiver:args:, #<span>tryPrimitive:withArgs:/</span>#<span>tryNamedPrimitiveIn:for:withArgs:,
and #<span>simulateValueWithArguments:caller:</span> (and analogously to ExternalFunction >> #<span>tryInvokeWithArguments: and the critsect primitive methods on Mutex)?</span></span></span></span></span></div></div></div></div></div></div></div></div></blockquote><div><font size="4"><br></font></div><div class="gmail_default"><font size="4">We can, but remember that passing a block is in fact hiding an allocation, maybe two. Mentioning a block in code causes it to be allocated and if not already done so, causes allocation of the lexically enclosing context.</font></div><div class="gmail_default"><font size="4"></font></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif" dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div id="gmail-m_-2979770936573098614Signature"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div name="divtagdefaultwrapper"><div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt">Then we could rewrite #<span style="font-size:12pt">send:to:with:lookupIn: like this (pseudo):</span></div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody"><span style="font-family:"Times New Roman"">send: selector to: rcvr with: arguments lookupIn: lookupClass</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> "Simulate the action of sending a message with selector and arguments to rcvr. The argument, lookupClass, is the class in which to lookup the message. This is the receiver's class for normal
messages, but for super messages it will be some specific class related to the source method."</span><br style="font-family:"Times New Roman"">
<br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> | meth <span style="color:rgb(189,19,152)">
prim</span><span style="color:rgb(189,19,152)">FailCode</span><span style="color:rgb(189,19,152)">
</span><span style="color:rgb(0,0,0)">val </span>ctxt |</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> (meth := lookupClass lookupSelector: selector) ifNil:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> [selector == #doesNotUnderstand: ifTrue:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> [self error: 'Recursive message not understood!' translated].</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> ^self send: #doesNotUnderstand:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> to: rcvr</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> with: {(Message selector: selector arguments: arguments) lookupClass: lookupClass}</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> lookupIn: lookupClass].</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> </span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> meth isCompiledMethod ifFalse:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> ["Object as Methods (OaM) protocol: 'The contract is that, when the VM encounters an ordinary object (rather than a compiled method) in the method dictionary during lookup, it sends it the
special selector #run:with:in: providing the original selector, arguments, and receiver.'. DOI: 10.1145/2991041.2991062."</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> ^self send: #run:with:in:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> to: meth</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> with: {selector. arguments. rcvr}].</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> </span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> meth numArgs = arguments size ifFalse:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> [^ self error: ('Wrong number of arguments in simulated message {1}' translated format: {selector})].</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> (primIndex := meth primitive) > 0 ifTrue:</span><br style="font-family:"Times New Roman"">
<s style="font-family:"Times New Roman""><font color="#0000FF">- [val := self doPrimitive: primIndex method: meth receiver: rcvr args: arguments.<br>
- (self isPrimFailToken: val) ifFalse:<br>
- [^val]].<br>
</font></s><font color="#FF0000" style="font-family:"Times New Roman"">+ [val := self doPrimitive: primIndex method: meth receiver: rcvr args: arguments ifFail:<br>
+ [:code | primFailCode := code].</font></div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody"><font color="#FF0000" style="font-family:"Times New Roman"">+ primFailCode ifNil: [^ val]].<br>
</font><span style="font-family:"Times New Roman""> </span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> (selector == #doesNotUnderstand: and: [lookupClass == ProtoObject]) ifTrue:</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> [^self error: ('Simulated message {1} not understood' translated format: {arguments first selector})].</span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> </span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> ctxt := Context sender: self receiver: rcvr method: meth arguments: arguments.</span><br style="font-family:"Times New Roman"">
<s style="font-family:"Times New Roman""><font color="#0000FF">- (primIndex isInteger and: [primIndex > 0]) ifTrue:<br>
- [ctxt failPrimitiveWith: val].<br>
</font></s><font color="#FF0000" style="font-family:"Times New Roman"">+ primFailCode ifNotNil:<br>
+ [ctxt failPrimitiveWith: primFailCode].<br>
</font><span style="font-family:"Times New Roman""> </span><br style="font-family:"Times New Roman"">
<span style="font-family:"Times New Roman""> ^ctxt</span><br>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody"><span><span>Current senders of #<span>primitiveFailTokenFor: could then evaluate the failBlock if the primitive fails.</span></span></span></div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody"><span><span>Do you think this approach would be worth a try? :-)</span></span></div></div></div></div></div></div></div></div></blockquote><div><font size="4"><br></font></div><div class="gmail_default"><font size="4">Definitely. It might eliminate multiple tests. I think you should definitely try it. It looks nice to me. Thank you!</font></div><div class="gmail_default"><font size="4"></font></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div id="gmail-m_-2979770936573098614divtagdefaultwrapper" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif" dir="ltr"><div dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div><div dir="ltr" style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols"><div name="divtagdefaultwrapper"><div>
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<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span><span>Best,</span></span></div>
<div id="gmail-m_-2979770936573098614Item.MessagePartBody" style="font-size:12pt"><span><span>Christoph</span></span></div>
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<div id="gmail-m_-2979770936573098614divRplyFwdMsg" dir="ltr" style="font-size:12pt"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Von:</b> Squeak-dev <<a href="mailto:squeak-dev-bounces@lists.squeakfoundation.org" target="_blank">squeak-dev-bounces@lists.squeakfoundation.org</a>> im Auftrag von Eliot Miranda <<a href="mailto:eliot.miranda@gmail.com" target="_blank">eliot.miranda@gmail.com</a>><br>
<b>Gesendet:</b> Freitag, 1. Januar 2021 22:34:28<br>
<b>An:</b> The general-purpose Squeak developers list<br>
<b>Betreff:</b> Re: [squeak-dev] Two new curious Context/primitive questions :-)</font>
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<div style="font-size:small">errata:<br>
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<div class="gmail_attr">On Fri, Jan 1, 2021 at 1:22 PM Eliot Miranda <<a href="mailto:eliot.miranda@gmail.com" target="_blank">eliot.miranda@gmail.com</a>> wrote:<br>
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<span style="font-size:large">Hi Christoph,</span><br>
<font size="4"><br>
</font><span style="font-size:large"> happy new year!!</span><br>
<font size="4"><br>
</font><span style="font-size:large">On Fri, Jan 1, 2021 at 11:28 AM Thiede, Christoph <</span><a href="mailto:Christoph.Thiede@student.hpi.uni-potsdam.de" target="_blank">Christoph.Thiede@student.hpi.uni-potsdam.de</a><span style="font-size:large">> wrote:</span><br>
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<div class="gmail_quote"><span style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif">Hi all, hi Eliot,</span><br>
<font color="#000000" face="Calibri, Helvetica, sans-serif" size="3"><span><br>
</span></font><span style="font-size:12pt;color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif">new year, new simulation fun, and I have collected two new questions about the Context implementation which I'd love to get answered here:</span><br>
<font color="#000000" face="Calibri, Helvetica, sans-serif" size="3"><span><br>
</span></font><span style="font-size:12pt;color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif">First, I was confused by the following:</span><br>
<span style="font-family:Calibri,Helvetica,sans-serif,EmojiFont,"Apple Color Emoji","Segoe UI Emoji",NotoColorEmoji,"Segoe UI Symbol","Android Emoji",EmojiSymbols;font-size:16px;color:rgb(0,0,0)">(BlockClosure >> #numArgs) primitive. "266"</span><br>
<span style="font-size:12pt;color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif">(Context >> #pc) primitive. "0"</span><br>
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<div style="font-size:12pt">What makes Context so special that it cannot be compiled with quick accessor methods?</div>
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<font size="4"><br>
</font><span style="font-size:large">The gory details are here: </span><a href="http://www.mirandabanda.org/cogblog/2009/01/14/under-cover-contexts-and-the-big-frame-up/" target="_blank">http://www.mirandabanda.org/cogblog/2009/01/14/under-cover-contexts-and-the-big-frame-up/</a><br>
<font size="4"><br>
</font><span style="font-size:large">But that's full of implementation detail. Let me try and explain at a higher level.</span><br>
<font size="4"><br>
</font><span style="font-size:large">Contexts are wonderful but very expensive. Any VM that actually creates contexts for every method or block activation will inevitably run slowly. There are two overheads here. One is the basic overhead of allocating and
reclaiming the contexts that are created. The other is the cost of moving the outgoing receiver and arguments from the sending context to the new context. A fast VM must avoid these overheads, and the key solution is to use a stack frame organization as
is used in conventional language implementations. The key here is that with stack frames the receiver and incoming arguments do not have to be moved; they stay where they are and a new frame is built underneath them which includes them as the incoming receiver
and arguments; stack frames overlap outgoing and incoming arguments.</span><br>
<font size="4"><br>
</font><span style="font-size:large">But crucially, in addition the VM must still create contexts if and when they are needed. If not, this would no longer be a Smalltalk-80 implementation. Now one could imagine a VM which converted stack frames to contexts
whenever a method or block activation was accessed using thisContext (or thisContext sender etc which access contexts by following the sender field). But that would be very slow. Instead, the fastest approach is to try and keep stack frames as stack frames
for as long as possible. For this to work contexts have to be able to function as "proxy objects" for stack frames. The VM does indeed create contexts when one uses thisContext, or even when one creates a block, but internally the context is in a very special
state, a state in which it points at a stack frame.</span><br>
<font size="4"><br>
</font><span style="font-size:large">Some terminology is useful. Peter Deutsch used "volatile", "hybrid" and "stable". I like "single", "married", "widowed" and "divorced" (Peter's scheme didn't have "widowed" which is the key to why my scheme is faster,
and why the closure implementation is as it is).</span><br>
<font size="4"><br>
</font><span style="font-size:large">When a stack frame is created it is "single". It has a slot within it to refer to a context object if it is needed, but the slot is nil.</span><br>
<span style="font-size:large">When a stack frame needs a context object one is created and the two are "married".</span><br>
<span style="font-size:large">When a method or block returns its stack frame is discarded; the stack frame has died and if it was married its context becomes "widowed". (*)</span><br>
<span style="font-size:large">When space is needed for new stack frames all reclaimed stack frames are "divorced" from their contexts. The stack frame state is written to the context object and the context object no longer acts as a proxy; it is a fully fledged
normal stack object. (*)</span><br>
<font size="4"><br>
</font><span style="font-size:large">(*) Stack frames exist in a small memory zone organized as stack pages, the stack zone. The size of the stack zone is set at startup, and its size is either the VM's defau<span class="gmail_default" style="font-size:small">l</span>t
or set by a value that persists in the image header (see vmParameterAt: 43). Since the system may run out of stack pages (a deep call stack, many active processes), the VM makes new pages available by purging the least recently used pages to the heap in the
form of context objects. All the frames in the least recently used stack page are divorced at the same time. A context must be created for each frame that is not ye</span><font size="4">t marrie<span class="gmail_default">d</span><span class="gmail_default"></span><span class="gmail_default"></span>.<span class="gmail_default"></span><span class="gmail_default">
A page is big enough to hold on average about 40 method activations; since activations are of different sizes and change size as execution proceeds, the number of activations per full page varies.</span></font><br>
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(*) The reason why Peter's original scheme is slower is that <span class="gmail_default">
in HPS </span>at return time the VM has to check for <span class="gmail_default">
a frame </span>being <span class="gmail_default">hybrid</span> and copy state to the hybrid context, making it stable. This has to be done because a closure's outer temporary variables are stored in the lexically enclosing stack frame, and so have to be made
to persist in the stable context or their values will be stale. In my (lisp-derived) closure implementation there are no such references to outer temporary variables; values are either copied if they do not change, or stored in an Array (the "indirection
vector"), which can then be copied.<br>
<br>
Note that divorce is a process. Once divorced a context is single and free to function as a context does. Indeed when the system starts up it loads an image which only contains single contexts. All contexts are divorced on snapshot.<span class="gmail_default">
Divorced contexts are amnesiacs.</span><span class="gmail_default"></span><br>
<br>
<br>
</font><span style="font-size:large">So now, finally, we can answer your question. Why is (Context>>#pc), a method that simply answers an instance variable, not compiled as a quick method with a primitive that answers that variable? "married" and "widowed"
contexts are proxies for stack frames. Only the instance variables they contain which do not change can be fetched from the context object itself; these are the receiver, arguments, closureOrNil, and method. sender, pc, stackp and other stack contents may
change as execution proceeds. These mutable values must be fetched from the stack frame itself, if it still exists.</span><br>
<font size="4"><br>
</font><span style="font-size:large">All accesses to sender, pc, stackp, and stack contents (Context>>at:[put:]) must be mediated. A married or widowed context has its sender field set to the frame pointer of its stack frame, encoded as a SmallInteger. You
can never see this from the image (except via a special xRay primitive). By following the frame pointer encoded in the sender field the VM can detect if the frame is still live. If so, the relevant values are synthesized or fetched from the stack frame itself.
If not, the context is widowed and "mourns"; it is changed into a context with a nil sender field, a nil pc, and a stackp that points at the last argument.</span><br>
<font size="4"><br>
</font><span style="font-size:large">How is this mediation done? One design could be to require that all image level accesses to Context inst vars are through primitives. This feels contrived to me. Instead, inst var access is via inst var access bytcodes.
But if we do this naively we would have to check in all inst var access bytecodes whose index is the same as sender (0), pc (1) & stackp (2). This would slow down inst var access enormously. Instead we observe that inst var access bytecodes pushReceiverVariable:,
popIntoReceiverVariable: have short forms for the most frequently used (indexes 0 to 15 for push, indexes 0 to 7 for popInto). By arranging that we only use the long forms for accessing inst vars in Context, and superclasses and subclasses, we only have to
check in the long forms and the check is cheap. We check that the index is <= 2, because all other inst var accesses with these indices will use the short-form bytecodes.</span><br>
<font size="4"><br>
</font><span style="font-size:large">By arranging that Context's inst vars are *not* accessed by quick primitives we do not have to duplicate this machinery in quick primitive dispatch, which would also slow things down. Hence Context>>pc is compiled as a
vanilla method and its inst var access bytecode is the long form:</span><br>
<font size="4"><br>
</font><span style="font-size:large">25 <E2 01> pushRcvr: 1</span><br>
<span style="font-size:large">27 <5C> returnTop</span><br>
<br>
<span style="font-size:large">'Nuff said</span></div>
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<span style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif;font-size:12pt">Second, Context >> #</span><span style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif;font-size:12pt">isPrimFailToken: attracted my attention multiple times
when looking at different #timeProfile results of simulation sessions. In the expression [100000 factorial] it takes up more than 44% of the whole execution time!</span><br>
<span style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif;font-size:12pt">I have no idea why it could be so slow, but this message is sent really often, which is at least 2 times per simulation of a special message send.</span><br>
<span style="color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif;font-size:12pt">Would there be an easy change to resolve this bottleneck and speed up the simulation by 40% or more?</span><br>
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<div><span><span>Would it be possible to provide a primitive for this method? Or do you see any other way to optimize it?</span></span></div>
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It's not slow so much as <span class="gmail_default">that </span>it has to be used all the time to check whether a send has invoked a primitive which has failed. Its function is to support primitive error codes.
<span class="gmail_default">Before primitive error codes</span> <span class="gmail_default">(IIRC)
</span>we simply check<span class="gmail_default">ed</span> for nil. But with <span class="gmail_default" style="color:rgb(0,0,0)">primitive error codes</span><span style="color:rgb(0,0,0);font-family:-webkit-standard"> </span> we need a container that both
reliably distinguishes a primitive failure result from all other objects in the system, and holds onto the primitive failure code. It may indeed be able to reduce the overhead by only testing when absolutely necessary. It may be that reimplementing the scheme
is faster.</font><br>
<font size="4"><br>
</font><span style="font-size:large">For example, one could imagine a class whose instances are the only objects to answer #isPrimFailToken, which would be faster than a one argument message send. But beware, because if one was debugging the debugger one mustn't
confuse a PrimFailToken created in the simulation for a PrimFailToken created by the simulation.</span><br>
<span style="font-size:large">Remember to distinguish between price and value. Implementing the context-to-stack mapping scheme outlined above was very costly, but its value is very high. It allows us to have contexts, with all their utility, while reducing
their costs significantly. Similarly, and closely related, being able to simulate execution is costly but hugely valuable. If the price is 40% of simulated execution then it is a price worth paying.</span><br>
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<span style="font-size:12pt;color:rgb(0,0,0);font-family:Calibri,Helvetica,sans-serif">Best,</span><br>
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<div><span><span>Christoph</span></span></div>
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</font><span style="font-size:large">Happy New Year!</span><br>
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</font><span style="font-size:large">_,,,^..^,,,_</span><br>
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<div>best, Eliot</div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><span style="font-size:small;border-collapse:separate"><div>_,,,^..^,,,_<br></div><div>best, Eliot</div></span></div></div></div></div>