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<title>avram - a virtual machine code interpreter: 3.7 Profiling</title>

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<a name="Profiling"></a>
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<hr size="1">
<a name="Profiling-1"></a>
<h2 class="section">3.7 Profiling</h2>

<a name="index-profile_002eh"></a>
<p>The functions declared in &lsquo;<tt>profile.h</tt>&rsquo; can be used for constructing
and writing tables of run time statistics such as those mentioned in
<a href="Files.html#Files">Files</a>, and <a href="Profile.html#Profile">Profile</a>. These functions maintain a database of
structures, each recording the statistics for a particular virtual code
fragment.
</p>
<p>Each structure in the database is identified by a unique key, which must
be a list representing a character string. A pointer to such a structure
<a name="index-score"></a>
is declared to be of type <code>score</code>. For the most part, the data
structure should be regarded as opaque by a client program, except for a
field <code>reductions</code> of type <code>counter</code>, which may be modified
arbitrarily by the client. 
</p>
<p>The way these operations are used in the course of evaluating virtual
code applications containing profile annotations is to add a structure
to the database each time a new profiled code fragment is encountered,
using the annotation as its key, and to increment the <code>reductions</code>
<a name="index-annotations-1"></a>
of the structure each time any constituent of the code gets a quantum of
work done on it. Other ways of using these operations are left to the
developer&rsquo;s discretion.
</p>
<dl>
<dt><a name="index-avm_005fentries"></a><u>Function:</u> score <b>avm_entries</b><i> (list <var>team</var>, list *<var>message</var>, int *<var>fault</var>)</i></dt>
<dd><p>This function retrieves or creates a data base entry given its key. The
parameters have these interpretations.
</p>
<dl compact="compact">
<dt> <code><var>team</var></code></dt>
<dd><p>is a list representing a character string that uniquely identifies the
database entry to be retrieved or created.
</p></dd>
<dt> <code><var>message</var></code></dt>
<dd><p>is the address of a list known to the caller, which will be assigned a
list representing an error message if any error occurs in the course of
searching the database or creating a new entry.
</p></dd>
<dt> <code><var>fault</var></code></dt>
<dd><p>is the address of an integer that will be set to a non-zero value if any
error is caused by this function.
</p></dd>
</dl>

<p>The pointer returned by this function is the address of the record whose
key is given by the <code><var>team</var></code> parameter. If such a record is
already in the database, its address is returned, but otherwise a new
one is created whose address is then returned. The <code>reductions</code>
field of a newly created entry will be zero.
</p>
<p>In the course of searching the database, the <code>avm_compare</code>
function is used, so the associated lists may be modified as noted in
<a href="Comparison.html#Comparison">Comparison</a>.  It is not necessary for a client to include the header
file &lsquo;<tt>compare.h</tt>&rsquo; or to call <code>avm_initialize_compare</code> in order
to use the profile operations, because they are done automatically.
</p>
<p>If an error message is assigned to the list referenced by
<code><var>message</var></code>, the integer referenced by <code><var>fault</var></code> will
be set to a non-zero value. The form of the error message will be a list
in which each item is a list of character representations as per
<a href="Character-Table.html#Character-Table">Character Table</a>. It is the responsibility of the caller to dispose
of the error message. Currently the only possible error is a memory
overflow, which in this case is non-fatal.
</p></dd></dl>
<dl>
<dt><a name="index-avm_005ftally"></a><u>Function:</u> void <b>avm_tally</b><i> (char *<var>filename</var>)</i></dt>
<dd><p>This function makes a table of the results stored in the data base built
by the <code>avm_entries</code> function. The argument is the address of a
null terminated character string containing the name of the file in
which the results will be written. A file is opened and the table is
written in a self explanatory text format, with columns labeled
&ldquo;reductions&rdquo; and &ldquo;invocations&rdquo; among others. The latter contains the
number of times the associated key was accessed through
<code>avm_entries</code>.
</p>
<p>The data written to the file should be taken with a grain of salt.  It
is computed using native integer and floating point arithmetic, with no
checks made for overflow or roundoff error, and no guarantee of cross
<a name="index-reductions"></a>
platform portability. The number of &ldquo;reductions&rdquo; means whatever the
developer of the client program wants it to mean.
</p>
<p>The following error messages are possible with this function, which will
be written to standard error. None of them is fatal.
<a name="index-can_0027t-write-5"></a>
<a name="index-can_0027t-close-2"></a>
<a name="index-invalid-profile-identifier-1"></a>
</p>
<ul>
<li> <code><var>program-name</var>: can't write <var>filename</var></code>
</li><li> <code><var>program-name</var>: can't write to <var>filename</var></code>
</li><li> <code><var>program-name</var>: can't close <var>filename</var></code>
</li><li> <code><var>program-name</var>: invalid profile identifier</code>
</li></ul>

<p>The last message is reported if any record in the database has a key
that is not a list of valid character representations. The others are
<a name="index-strerror-5"></a>
accompanied by an explanation from the standard <code>strerror</code> function
if possible.
</p></dd></dl>
<dl>
<dt><a name="index-avm_005finitialize_005fprofile"></a><u>Function:</u> void <b>avm_initialize_profile</b><i> ()</i></dt>
<dd><p>This function should be called before any of the other functions in this
section in order to initialize the data base. Results are undefined if
it is not called first.
</p></dd></dl>
<dl>
<dt><a name="index-avm_005fcount_005fprofile"></a><u>Function:</u> void <b>avm_count_profile</b><i> ()</i></dt>
<dd><p>This function can be called after the other functions in this section as
a way of detecting memory leaks. If any storage remains unreclaimed that
was created by the functions in this section, a warning message is
written to standard error. If the <code>avm_count_lists</code> function is
being used by the client program, it should be called after this one.
</p></dd></dl>

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