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<h3 class="section">3.7 Profiling</h3>

<p><a name="index-g_t_0040file_007bprofile_002eh_007d-616"></a>The functions declared in <samp><span class="file">profile.h</span></samp> 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>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-g_t_0040code_007bscore_007d-617"></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>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-618"></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's discretion.

<div class="defun">
&mdash; Function: score <b>avm_entries</b> (<var>list team, list *message, int *fault</var>)<var><a name="index-avm_005fentries-619"></a></var><br>
<blockquote><p>This function retrieves or creates a data base entry given its key. The
parameters have these interpretations.

          <dl>
<dt><var>team</var><dd>is a list representing a character string that uniquely identifies the
database entry to be retrieved or created. 
<br><dt><var>message</var><dd>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. 
<br><dt><var>fault</var><dd>is the address of an integer that will be set to a non-zero value if any
error is caused by this function. 
</dl>

        <p>The pointer returned by this function is the address of the record whose
key is given by the <var>team</var> 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>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 <samp><span class="file">compare.h</span></samp> or to call <code>avm_initialize_compare</code> in order
to use the profile operations, because they are done automatically.

        <p>If an error message is assigned to the list referenced by
<var>message</var>, the integer referenced by <var>fault</var> 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></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_tally</b> (<var>char *filename</var>)<var><a name="index-avm_005ftally-620"></a></var><br>
<blockquote><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>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-621"></a>platform portability. The number of &ldquo;reductions&rdquo; means whatever the
developer of the client program wants it to mean.

        <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-g_t_0040code_007bcan_0027t-write_007d-622"></a><a name="index-g_t_0040code_007bcan_0027t-close_007d-623"></a><a name="index-g_t_0040code_007binvalid-profile-identifier_007d-624"></a>
          <ul>
<li><var>program-name</var><code>: can't write </code><var>filename</var>
<li><var>program-name</var><code>: can't write to </code><var>filename</var>
<li><var>program-name</var><code>: can't close </code><var>filename</var>
<li><var>program-name</var><code>: invalid profile identifier</code>
</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-g_t_0040code_007bstrerror_007d-625"></a>accompanied by an explanation from the standard <code>strerror</code> function
if possible. 
</p></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_initialize_profile</b> ()<var><a name="index-avm_005finitialize_005fprofile-626"></a></var><br>
<blockquote><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></blockquote></div>

<div class="defun">
&mdash; Function: void <b>avm_count_profile</b> ()<var><a name="index-avm_005fcount_005fprofile-627"></a></var><br>
<blockquote><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></blockquote></div>

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