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Estimated hours taken: 4 Translated plain text docs to HTML. This obviously creates a dual update problem. We should solve this by putting the plain text docs in the attic and retaining the HTML. Also added the HTML files to the Mmakefile so they are installed on the web pages. The other documents in compiler/notes will be HTMLized soon. compiler/notes/ Mmakefiles ALLOCATION.html AUTHORS.html CODING_STANDARDS.html COMPILER_DESIGN.html GC_AND_C_CODE.html GLOSSARY.html MODULE_SYSTEM.html RELEASE_CHECKLIST.html REVIEWS.html TODO.html
76 lines
1.6 KiB
HTML
76 lines
1.6 KiB
HTML
<html>
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<head>
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<title>
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Information On Garbage Collection And C Code
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</title>
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</head>
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<body
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bgcolor="#ffffff"
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text="#000000"
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>
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<hr>
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<!-------------------------->
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When handwritten code is called from Mercury, the garbage collection
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scheduler doesn't know anything about the code, so it cannot replace
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the succip on the stack (if there is one) with the collector's address.
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<p>
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If the handwritten code calls no other code, then this is fine, the
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scheduler knows it can replace the succip variable and when a
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proceed() occurs execution will return to mercury code which it
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knows about.
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<p>
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If handwritten code calls other handwritten code, we have a problem,
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as succip will be saved on the stack and we don't know where on
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the stack it is stored. So we use a global variable 'saved_succip' which
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is succip is saved into. Care must be taken to save saved_succip on the
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stack so it doesn't get clobbered. <br>
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So
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<pre>
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detstackvar(1) = (int) succip;
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</pre>
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becomes
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<pre>
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detstackvar(1) = (int) saved_succip;
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saved_succip = (int) succip;
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</pre>
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and, when restoring,
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<pre>
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succip = (int) detstackvar(1);
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</pre>
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becomes
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<pre>
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succip = saved_succip;
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saved_succip = detstackvar(1);
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</pre>
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(With appropriate LVALUE_CASTs).
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<p>
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In this way, garbage collection always knows where the succip is stored
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in handwritten code.
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<p>
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The garbage collection code must check that the current execution is not
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still in a handwritten predicate - if it is, it must re-schedule (essentially
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just the same as before).
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<p>
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<hr>
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<!-------------------------->
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Last update was $Date: 1997-04-03 05:17:37 $ by $Author: aet $@cs.mu.oz.au. <br>
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</body>
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</html>
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