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<title>Analysis - Exploring Improvements</title>
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<span class="productTitle">ExpTreeLib Demo</span><br />
<span class="topicTitle">Exploring Improvements</span><br />
<p>
<a href="../Exp_Index.htm">ExpLib and Demo Package</a><--
<a href="ImprovingResponsiveness.htm">Improving Responsiveness</a><--
<a href="Responsiveness.htm">Responsiveness Analysis</a><--
Analysis - Exploring Improvements
--><a href="Analysis3.htm">Analysis - Beyond FileInfo</a>
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<h3><a id = "BkMrk_1">Exploring Improvements</a></h3>
<p>The Table on the <a href="Analysis1.htm">previous page</a> clearly shows that the
<b>GenItems</b> phase is the major contributor to any delay in responsiveness.
The major activities of this phase for the Demo Forms are:</p>
<ol>
<li>Acquiring the File Length and Date information by querying those properties for
each of the relevant CShItem instance. CShItem obtains the values of those
Properties by creating a FileInfo instance. Any reference to these properties
will, if the Value has not previously been obtained, create a FileInfo, extract
all File Length and Date Values, and Set the Property Values with those obtained
from the FileInfo. Note that any reference to any of the Properties in question
will fill all relevant Property Values. In short, a new FileInfo will be created
exactly once for the lifetime of the CShItem.</li>
<li>Using the <code>GetAttr</code> VB.Net function to obtain the <code>FileAttributes</code> of each of the
required Files and Directories. Note that most applications will not need to
know the state of the Archive bit for any File. Most Attribute information is
already available from existing CShItem Properties (IsSystem, IsReadOnly,
IsHidden, etc.). The Archive bit is not reported by the mechanism that CShItem
uses to obtain the other Attribute information and is the sole reason for using
<code>GetAttr</code>. However, the Demo Forms display these Attributes and therefore do call
<code>GetAttr</code>.*</li>
<li>Building the ListViewItems that are displayed in the ListView. This portion of
<b>GenItems</b> does not contribute in a noticible way to any delay and is
unavoidable in any case.</li>
</ol>
<h3><a id = "BkMrk_2">FileInfo</a></h3>
<p>As described above, an instance of the FileInfo Class is created the <i>first</i> time any of several CShItem Properties
is queried by the application. Note that certain reported changes to a File may cause another FileInfo creation, but that
is rare and of no interest to this discussion.</p>
<p>Previous investigation had shown that when <i>each</i> FileInfo instance is
created, the FileInfo constructor will call the GetFileAttributesEX API to
obtain a Win32_File_Attribute_Data structure. This structure is a subset of the
Win32_Find_Data structure and is probably obtained by using the
FindFirstFile/FindNextFile API (FFF/FNF) routines or close variant. In effect, a
SafeFindHandle for the item's parent Folder must be obtained to obtain the
desired data. It is during the creation of that SafeFindHandle that almost all
checks are made to determine if the calling application/user is Authorized to
obtain this information. In the case of a Local parent Folder, these check are
performed fairly quickly. In the case of a Remote parent Folder, the time to
create the Handle (and check for Authorization) can increase dramatically.</p>
<p>To test how much improvement was possible using FFF/FNF in the test cases, I
modified my testing Form. The results are discussed on the
<a href="Analysis3.htm">next page</a>.</p>
<h3><a name = "GetAttr">GetAttr</a></h3>
<p>The use of the GetAttr function in the Demo Forms stems from a design issue in
CShItem. The Attributes Property of CShItem reports the attributes found using
using the IShFolder.GetAttributesOf function. This is exactly what is needed for
CShItem's purposes, but has little relationship to the .Net FileAttributes Class
as returned by GetAttr or by FileInfo.Attributes or in the Win32_Find_Data
structure (all of which are identical). The problem is that CShItem.Attributes
as currently implemented is of no use outside of CShItem. That property should
be built by CShItem at the same time as all other CShItem Properties that are
extracted from a FileInfo. </p>
<p>As related to the time tests, the use of GetAttr will have an effect on the time
spent in <b>GenItems</b>. In the last phase of this effort, I modified CShItem to obtain Attribute
information from the FileInfo, eliminating the need for a separate GetAtt call.
In limited testing, this reduced the time until the GUI was responsive by 7% to
16%.</p>
<p> </p>
<p><b>See Also:</b></p>
<p style="margin-left:2em"><a href="Analysis3.htm">Alternatives </a></p>
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After 30+ years working in the IT field, mostly managing SysAdmins, I have retired. One of my hobbies returns me to programming, basically just to keep my hand in.
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