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---
layout: default
---
<?xml version="1.0" encoding="utf8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!--http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd-->
<html xmlns="http://www.w3.org/1999/xhtml"
>
<head><title>20 Building a Hybrid Collector</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf8" />
<meta name="generator" content="TeX4ht (https://tug.org/tex4ht/)" />
<meta name="originator" content="TeX4ht (https://tug.org/tex4ht/)" />
<!-- xhtml,charset=utf8,2,html -->
<meta name="src" content="index.tex" />
<link rel="stylesheet" type="text/css" href="index.css" />
</head><body
>
<!--l. 2--><div class="crosslinks"><p class="noindent"></p></div>
<h2 class="chapterHead"><span class="titlemark">Chapter 20</span><br /><a
id="x24-26400020"></a>Building a Hybrid Collector</h2>
<!--l. 5--><p class="noindent" >Extend the Tutorial plan to create a ”copy-MS” collector, which allocates into a
copying nursery and at collection time, copies nursery survivors into a mark-sweep
space. This plan does not require a write barrier (it is not strictly generational, as it
will collect the whole heap each time the heap is full). Later we will extended
it with a write barrier, allowing the nursery to be collected in isolation.
Such a collector would be a generational mark-sweep collector, similar to
GenMS.
</p>
<h3 class="sectionHead"><span class="titlemark">20.1 </span> <a
id="x24-26500020.1"></a>Add a Copying Nursery</h3>
<!--l. 9--><p class="noindent" >This step will change your simple collector from using a bump pointer to a free list
(but still without any garbage collection).
</p><!--l. 11--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x24-265002x1">In <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">TutorialConstraints</span></span></span>, make the following changes:
<ol class="enumerate2" >
<li
class="enumerate" id="x24-265004x1">Override the <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">movesObjects()</span></span></span> method to return <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">true</span></span></span>, reflecting that we
are now building a copying collector: <!--l. 15-->
<div class="lstlisting" id="listing-175"><span class="label"><a
id="x24-265005r1"></a></span><span
class="cmtt-10">@Override</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-265006r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">boolean</span><span
class="cmtt-10"> </span><span
class="cmtt-10">movesObjects</span><span
class="cmtt-10">()</span><span
class="cmtt-10"> </span><span
class="cmtt-10">{</span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">true</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><span
class="cmtt-10">}</span>
</div>
</li>
<li
class="enumerate" id="x24-265008x2">Remove the restriction on default alloc bytes (since default allocation will
now go to a bump-pointed space). To do this, remove the override of
<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">maxNonLOSDefaultAllocBytes()</span></span></span>.
</li>
<li
class="enumerate" id="x24-265010x3">Add a restriction on the maximum size that may be copied into the
(default) non-LOS mature space: <!--l. 21-->
<div class="lstlisting" id="listing-176"><span class="label"><a
id="x24-265011r1"></a></span><span
class="cmtt-10">@Override</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-265012r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">maxNonLOSCopyBytes</span><span
class="cmtt-10">()</span><span
class="cmtt-10"> </span><span
class="cmtt-10">{</span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">SegregatedFreeListSpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">MAX_FREELIST_OBJECT_BYTES</span><span
class="cmtt-10">;}</span>
</div>
</li></ol>
</li>
<li
class="enumerate" id="x24-265014x2">In <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">Tutorial</span></span></span>, add a nursery space:
<ol class="enumerate2" >
<li
class="enumerate" id="x24-265016x1">Create a new space, <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nurserySpace</span></span></span>, of type <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">CopySpace</span></span></span>. The new space
will initially be a from-space, so provide <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">false</span></span></span> as the third argument.
Initialize the space with a contiguous virtual memory region consuming
0.15 of the heap by passing ”0.15” and ”true” as arguments to the
constructor of VMRequest(more on this later). Create and initialize a
new integer constant to hold the descriptor for this new space:
<!--l. 29-->
<div class="lstlisting" id="listing-177"><span class="label"><a
id="x24-265017r1"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">static</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">CopySpace</span><span
class="cmtt-10"> </span><span
class="cmtt-10">nurserySpace</span><span
class="cmtt-10"> </span><span
class="cmtt-10">=</span><span
class="cmtt-10"> </span><span
class="cmtt-10">new</span><span
class="cmtt-10"> </span><span
class="cmtt-10">CopySpace</span><span
class="cmtt-10">(</span><span
class="cmtt-10">"</span><span
class="cmtt-10">nursery</span><span
class="cmtt-10">"</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">false</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">VMRequest</span><span
class="cmtt-10">.</span><span
class="cmtt-10">highFraction</span><span
class="cmtt-10">(0.15</span><span
class="cmtt-10">f</span><span
class="cmtt-10">)</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-265018r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">static</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">NURSERY</span><span
class="cmtt-10"> </span><span
class="cmtt-10">=</span><span
class="cmtt-10"> </span><span
class="cmtt-10">nurserySpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">getDescriptor</span><span
class="cmtt-10">()</span><span
class="cmtt-10">;</span>
</div>
</li>
<li
class="enumerate" id="x24-265020x2">Add the necessary import statements
</li>
<li
class="enumerate" id="x24-265022x3">Add <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nurserySpace</span></span></span> to the <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">PREPARE</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">RELEASE</span></span></span> phases of
<span
class="cmtt-10">collectionPhase()</span>, prior to the existing calls to msTrace. Pass true to
nurserySpace.prepare() indicating that the nursery is a <span
class="cmti-10">from-space </span>during
collection.
</li>
<li
class="enumerate" id="x24-265024x4">Fix accounting so that <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">Tutorial</span></span></span> accounts for space consumed by
<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nurserySpace</span></span></span>:
<ol class="enumerate3" >
<li
class="enumerate" id="x24-265026x1">Add <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nurserySpace</span></span></span> to the equation in <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">getPagesUsed()</span></span></span></li></ol>
</li>
<li
class="enumerate" id="x24-265028x5">Since initial allocation will be into a copying space, we need to account for
copy reserve:
<ol class="enumerate3" >
<li
class="enumerate" id="x24-265030x1">Add a method to override <span
class="cmtt-10">getCollectionReserve() </span>which
returns <span
class="cmtt-10">nurserySpace.reservedPages() +</span>
<span
class="cmtt-10">super.getCollectionReserve()</span>
</li>
<li
class="enumerate" id="x24-265032x2">Add a method to override <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">getPagesAvail()</span></span></span>, returning
<span
class="cmtt-10">getTotalPages() - getPagesReserved()) >> 1</span>;</li></ol>
</li></ol>
</li></ol>
<!--l. 49--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">20.2 </span> <a
id="x24-26600020.2"></a>Add nursery allocation</h3>
<!--l. 51--><p class="noindent" >In <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">TutorialMutator</span></span></span>, replace the free-list allocator (<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">MarkSweepLocal</span></span></span>) with a nursery
allocator: Use an instance of <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">CopyLocal</span></span></span>, calling it <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nursery</span></span></span>. The constructor
argument should be <span
class="cmtt-10">Tutorial.nurserySpace</span>:
</p><ol class="enumerate1" >
<li
class="enumerate" id="x24-266002x1">change <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">alloc()</span></span></span> to use <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nursery.alloc()</span></span></span> rather than <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">ms.alloc()</span></span></span>.
</li>
<li
class="enumerate" id="x24-266004x2">remove the call to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">msSpace.postAlloc()</span></span></span> from <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">postAlloc()</span></span></span> since there
is no special post-allocation work necessary for the new copy space. The
call to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">super.postAlloc()</span></span></span> should remain conditional on <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">allocator !=</span>
<span
class="cmtt-10">Tutorial.ALLOC_DEFAULT</span></span></span>.
</li>
<li
class="enumerate" id="x24-266006x3">change the check within <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">getAllocatorFromSpace()</span></span></span> to check against
<span
class="cmtt-10">Tutorial.nurserySpace </span>and to return <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nursery</span></span></span>.
</li>
<li
class="enumerate" id="x24-266008x4">adjust <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">collectionPhase</span></span></span>
<ol class="enumerate2" >
<li
class="enumerate" id="x24-266010x1">replace call to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">ms.prepare()</span></span></span> with <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nursery.reset()</span></span></span>
</li>
<li
class="enumerate" id="x24-266012x2">remove call to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">ms.release()</span></span></span> since there are no actions necessary for
the nursery allocator upon release.</li></ol>
</li></ol>
<!--l. 64--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">20.3 </span> <a
id="x24-26700020.3"></a>Add copying to the collector</h3>
<!--l. 66--><p class="noindent" >In <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">TutorialCollector</span></span></span> add the capacity for the collector to allocate (copy), since our
new hybrid collector will perform copying.
</p><!--l. 68--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x24-267002x1">Add local allocators for both large object space and the mature space:
<!--l. 70-->
<div class="lstlisting" id="listing-178"><span class="label"><a
id="x24-267003r1"></a></span><span
class="cmtt-10">private</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">LargeObjectLocal</span><span
class="cmtt-10"> </span><span
class="cmtt-10">los</span><span
class="cmtt-10"> </span><span
class="cmtt-10">=</span><span
class="cmtt-10"> </span><span
class="cmtt-10">new</span><span
class="cmtt-10"> </span><span
class="cmtt-10">LargeObjectLocal</span><span
class="cmtt-10">(</span><span
class="cmtt-10">Plan</span><span
class="cmtt-10">.</span><span
class="cmtt-10">loSpace</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267004r2"></a></span><span
class="cmtt-10">private</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">MarkSweepLocal</span><span
class="cmtt-10"> </span><span
class="cmtt-10">mature</span><span
class="cmtt-10"> </span><span
class="cmtt-10">=</span><span
class="cmtt-10"> </span><span
class="cmtt-10">new</span><span
class="cmtt-10"> </span><span
class="cmtt-10">MarkSweepLocal</span><span
class="cmtt-10">(</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">msSpace</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span>
</div>
</li>
<li
class="enumerate" id="x24-267006x2">Add an <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">allocCopy()</span></span></span> method that conditionally allocates to the LOS or mature
space: <!--l. 75-->
<div class="lstlisting" id="listing-179"><span class="label"><a
id="x24-267007r1"></a></span><span
class="cmtt-10">@Override</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267008r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Address</span><span
class="cmtt-10"> </span><span
class="cmtt-10">allocCopy</span><span
class="cmtt-10">(</span><span
class="cmtt-10">ObjectReference</span><span
class="cmtt-10"> </span><span
class="cmtt-10">original</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">bytes</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267009r3"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">align</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">offset</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">allocator</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><span
class="cmtt-10">{</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267010r4"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">if</span><span
class="cmtt-10"> </span><span
class="cmtt-10">(</span><span
class="cmtt-10">allocator</span><span
class="cmtt-10"> </span><span
class="cmtt-10">==</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Plan</span><span
class="cmtt-10">.</span><span
class="cmtt-10">ALLOC_LOS</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267011r5"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">los</span><span
class="cmtt-10">.</span><span
class="cmtt-10">alloc</span><span
class="cmtt-10">(</span><span
class="cmtt-10">bytes</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">align</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">offset</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267012r6"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">else</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267013r7"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">mature</span><span
class="cmtt-10">.</span><span
class="cmtt-10">alloc</span><span
class="cmtt-10">(</span><span
class="cmtt-10">bytes</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">align</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">offset</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267014r8"></a></span><span
class="cmtt-10">}</span>
</div>
</li>
<li
class="enumerate" id="x24-267016x3">Add a <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">postCopy()</span></span></span> method that conditionally calls LOS or mature space
post-copy actions: <!--l. 86-->
<div class="lstlisting" id="listing-180"><span class="label"><a
id="x24-267017r1"></a></span><span
class="cmtt-10">@Override</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267018r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">final</span><span
class="cmtt-10"> </span><span
class="cmtt-10">void</span><span
class="cmtt-10"> </span><span
class="cmtt-10">postCopy</span><span
class="cmtt-10">(</span><span
class="cmtt-10">ObjectReference</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">ObjectReference</span><span
class="cmtt-10"> </span><span
class="cmtt-10">typeRef</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267019r3"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">bytes</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">int</span><span
class="cmtt-10"> </span><span
class="cmtt-10">allocator</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><span
class="cmtt-10">{</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267020r4"></a></span><span
class="cmtt-10">if</span><span
class="cmtt-10"> </span><span
class="cmtt-10">(</span><span
class="cmtt-10">allocator</span><span
class="cmtt-10"> </span><span
class="cmtt-10">==</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Plan</span><span
class="cmtt-10">.</span><span
class="cmtt-10">ALLOC_LOS</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267021r5"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">Plan</span><span
class="cmtt-10">.</span><span
class="cmtt-10">loSpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">initializeHeader</span><span
class="cmtt-10">(</span><span
class="cmtt-10">object</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">false</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267022r6"></a></span><span
class="cmtt-10">else</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267023r7"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">msSpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">postCopy</span><span
class="cmtt-10">(</span><span
class="cmtt-10">object</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">true</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-267024r8"></a></span><span
class="cmtt-10">}</span>
</div>
</li></ol>
<!--l. 100--><p class="noindent" >
</p>
<h3 class="sectionHead"><span class="titlemark">20.4 </span> <a
id="x24-26800020.4"></a>Make necessary changes to TutorialTraceLocal</h3>
<!--l. 102--><p class="noindent" >
</p><ol class="enumerate1" >
<li
class="enumerate" id="x24-268002x1">Add nurserySpace clauses to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">isLive()</span></span></span> and <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">traceObject()</span></span></span>:
<ol class="enumerate2" >
<li
class="enumerate" id="x24-268004x1">Add the following to <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">isLive()</span></span></span>: <!--l. 106-->
<div class="lstlisting" id="listing-181"><span class="label"><a
id="x24-268005r1"></a></span><span
class="cmtt-10">if</span><span
class="cmtt-10"> </span><span
class="cmtt-10">(</span><span
class="cmtt-10">Space</span><span
class="cmtt-10">.</span><span
class="cmtt-10">isInSpace</span><span
class="cmtt-10">(</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">NURSERY</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">)</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-268006r2"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">nurserySpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">isLive</span><span
class="cmtt-10">(</span><span
class="cmtt-10">object</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span>
</div>
</li>
<li
class="enumerate" id="x24-268008x2">Add the following to traceObject(): <!--l. 111-->
<div class="lstlisting" id="listing-182"><span class="label"><a
id="x24-268009r1"></a></span><span
class="cmtt-10">if</span><span
class="cmtt-10"> </span><span
class="cmtt-10">(</span><span
class="cmtt-10">Space</span><span
class="cmtt-10">.</span><span
class="cmtt-10">isInSpace</span><span
class="cmtt-10">(</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">NURSERY</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">)</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-268010r2"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">nurserySpace</span><span
class="cmtt-10">.</span><span
class="cmtt-10">traceObject</span><span
class="cmtt-10">(</span><span
class="cmtt-10">this</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">ALLOC_DEFAULT</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span>
</div>
</li></ol>
</li>
<li
class="enumerate" id="x24-268012x2">Add a new <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">willNotMoveInCurrentCollection()</span></span></span> method, which identifies
those objects which do not move (necessary for copying collectors):
<!--l. 117-->
<div class="lstlisting" id="listing-183"><span class="label"><a
id="x24-268013r1"></a></span><span
class="cmtt-10">@Override</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-268014r2"></a></span><span
class="cmtt-10">public</span><span
class="cmtt-10"> </span><span
class="cmtt-10">boolean</span><span
class="cmtt-10"> </span><span
class="cmtt-10">willNotMoveInCurrentCollection</span><span
class="cmtt-10">(</span><span
class="cmtt-10">ObjectReference</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">)</span><span
class="cmtt-10"> </span><span
class="cmtt-10">{</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-268015r3"></a></span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10">return</span><span
class="cmtt-10"> </span><span
class="cmtt-10">!</span><span
class="cmtt-10">Space</span><span
class="cmtt-10">.</span><span
class="cmtt-10">isInSpace</span><span
class="cmtt-10">(</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">NURSERY</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">object</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span><span
class="cmtt-10"> </span><br /><span class="label"><a
id="x24-268016r4"></a></span><span
class="cmtt-10">}</span>
</div>
</li>
<li
class="enumerate" id="x24-268018x3">Modify <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">PlanSpecificConfig</span></span></span> to add the new <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">nursery</span></span></span> space: <!--l. 124-->
<div class="lstlisting" id="listing-184"><span class="label"><a
id="x24-268019r1"></a></span><span
class="cmtt-10">new</span><span
class="cmtt-10"> </span><span
class="cmtt-10">PlanSpecific</span><span
class="cmtt-10">(</span><span
class="cmtt-10">"</span><span
class="cmtt-10">org</span><span
class="cmtt-10">.</span><span
class="cmtt-10">mmtk</span><span
class="cmtt-10">.</span><span
class="cmtt-10">plan</span><span
class="cmtt-10">.</span><span
class="cmtt-10">tutorial</span><span
class="cmtt-10">.</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">"</span><span
class="cmtt-10">)</span><span
class="cmtt-10">.</span><span
class="cmtt-10">addExpectedSpaces</span><span
class="cmtt-10">(</span><span
class="cmtt-10">"</span><span
class="cmtt-10">ms</span><span
class="cmtt-10">"</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">"</span><span
class="cmtt-10">nursery</span><span
class="cmtt-10">"</span><span
class="cmtt-10">)</span><span
class="cmtt-10">,</span><span
class="cmtt-10"> </span><span
class="cmtt-10">"</span><span
class="cmtt-10">Tutorial</span><span
class="cmtt-10">"</span><span
class="cmtt-10">)</span><span
class="cmtt-10">;</span>
</div>
</li></ol>
<!--l. 129--><p class="noindent" >With these changes, <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">Tutorial</span></span></span> should now work. You should be able to again build a
<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">BaseBaseTutorial</span></span></span> image and test it against any benchmark. Again, if you use
<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">-X:gc:verbose=3</span></span></span> you can see the movement of data among the spaces at each
garbage collection.
</p>
<!--l. 145--><div class="crosslinks"><p class="noindent"></p></div>
<!--l. 145--><p class="noindent" ><a
id="tailBuildingAHybridCollector.html"></a></p>
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