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<!DOCTYPE concept
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<concept id="GUID-911CD800-2D1B-5D7B-A67C-66E01F91062C" xml:lang="en"><title>Heaps</title><shortdesc>The main thread of a process has a memory chunk that contains the
thread's heap. A program's request for memory is allocated from this heap.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Each thread has a chunk which contains that thread's program stack. For
the main thread of a process, this chunk also contains the thread's heap.
A program's request for memory is allocated from this heap. For example, a
code fragment such as: </p>
<codeblock id="GUID-ED3A8BC9-7601-5035-B422-ED80E5504867" xml:space="preserve">CArrayFixFlat&lt;...&gt;* fixflat;
...
fixflat = new (ELeave) CArrayFixFlat&lt;...&gt;(3);</codeblock>
<p>causes a portion of memory to be allocated from the heap and its address
returned to the caller. Memory from the heap must be explicitly requested
and, importantly, explicitly freed by the program. </p>
<p>If a process creates additional threads, then a new chunk is created for
each new thread. Each chunk contains the thread's stack; if a new thread is
not sharing an existing heap, then the chunk also contains a new heap. </p>
<p>When a new thread is created, either: </p>
<ul>
<li id="GUID-C915A4D8-70D9-55B4-A16F-9729B1F8D94B"><p>a new heap is created
for it </p> </li>
<li id="GUID-E72B8DF5-CB52-5333-9D3E-EFDBAFE6CB59"><p>it uses the creating
thread's heap </p> </li>
<li id="GUID-20C6F186-6EF6-511E-9291-3273CA930B5D"><p>it uses an explicitly
referenced heap. </p> </li>
</ul>
<p>A thread gets the handle to its heap by calling <xref href="GUID-C197C9A7-EA05-3F24-9854-542E984C612D.dita#GUID-C197C9A7-EA05-3F24-9854-542E984C612D/GUID-42AC433D-1C9C-3AC6-8640-EB1A7BA876B5"><apiname>User::Heap()</apiname></xref>. </p>
<p>See <xref href="GUID-D557CC2C-C045-5818-B2F7-9BD8BC39257D.dita">Address Space
and Process</xref> for more background on chunks and heaps.</p>
</conbody></concept>