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67 lines
1.8 KiB
HTML
67 lines
1.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<html>
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<head>
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<title>How to Relocate a File Data Structure</title>
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</head>
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<body>
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<h1>How to Relocate a File Data Structure</h1>
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<p>Since file data structures can be cached in memory by the H5AC
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package it becomes problematic to move such a data structure in
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the file. One cannot just copy a portion of the file from one
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location to another because:
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<ol>
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<li>the file might not contain the latest information, and</li>
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<li>the H5AC package might not realize that the object's
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address has changed and attempt to write the object to disk
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at the old address.</li>
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</ol>
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<p>Here's a correct method to move data from one location to
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another. The example code assumes that one is moving a B-link
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tree node from <code>old_addr</code> to <code>new_addr</code>.
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<ol>
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<li>Make sure the disk is up-to-date with respect to the
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cache. There is no need to remove the item from the cache,
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hence the final argument to <code>H5AC_flush</code> is
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<code>FALSE</code>.
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<br><br>
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<code>
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H5AC_flush (f, H5AC_BT, old_addr, FALSE);<br>
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</code>
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<br>
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</li>
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<li>Read the data from the old address and write it to the new
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address.
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<br><br>
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<code>
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H5F_block_read (f, old_addr, size, buf);<br>
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H5F_block_write (f, new_addr, size, buf);<br>
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</code>
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<br>
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</li>
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<li>Notify the cache that the address of the object changed.
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<br><br>
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<code>
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H5AC_rename (f, H5AC_BT, old_addr, new_addr);<br>
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</code>
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<br>
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</li>
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</ol>
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<hr>
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<address><a href="mailto:robb@maya.nuance.com">Robb Matzke</a></address>
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<!-- Created: Mon Jul 14 15:09:06 EST 1997 -->
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<!-- hhmts start -->
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Last modified: Mon Jul 14 15:38:29 EST
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<!-- hhmts end -->
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</body>
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</html>
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