Lists-of-Pairs-of-Ports.html 7.6 KB

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  57. <a name="Lists-of-Pairs-of-Ports-1"></a>
  58. <h3 class="subsection">3.8.1 Lists of Pairs of Ports</h3>
  59. <a name="index-port"></a>
  60. <p>A <code>port</code> is the name given to a type of pointer used in the library
  61. as the address of a place where a computational result yet to be
  62. evaluated will be sent. Ports are discussed further in <a href="Ports-and-Packets.html#Ports-and-Packets">Ports and Packets</a>,
  63. but are mentioned here because it is sometimes necessary to employ a
  64. list of pairs of them. A pointer to such a list is declared as a
  65. <code>portal</code> type. It refers to a structure of the form
  66. <a name="index-portal"></a>
  67. <a name="index-port_005fpair"></a>
  68. </p>
  69. <table><tr><td>&nbsp;</td><td><pre class="example">struct port_pair
  70. {
  71. port left;
  72. port right;
  73. portal alters;
  74. }
  75. </pre></td></tr></table>
  76. <p>A small selection of functions for <code>portal</code> memory management is
  77. declared as follows in the header file &lsquo;<tt>portals.h</tt>&rsquo;. For reasons of
  78. C-ness, the type declarations themselves are forced to be in
  79. &lsquo;<tt>lists.h</tt>&rsquo;.
  80. </p>
  81. <dl>
  82. <dt><a name="index-avm_005fnew_005fportal"></a><u>Function:</u> portal <b>avm_new_portal</b><i> (portal <var>alters</var>)</i></dt>
  83. <dd><p>This function is used to create storage for a new <code>port_pair</code>
  84. structure, and returns a <code>portal</code> pointer to it if successful. If
  85. the storage can&rsquo;t be allocated, a <code>NULL</code> pointer is returned.
  86. The <code>alters</code> field of the result is initialized as the given
  87. parameter supplied by the caller. All other fields are filled with zeros.
  88. </p></dd></dl>
  89. <dl>
  90. <dt><a name="index-avm_005fseal"></a><u>Function:</u> void <b>avm_seal</b><i> (portal <var>fate</var>)</i></dt>
  91. <dd><p>This function performs the reclamation of storage associated with
  92. <code>portal</code> pointers, either by freeing them or by consigning them
  93. temporarily to a local cache for performance reasons. Client programs
  94. should use only this function for disposing of <code>portal</code> storage
  95. rather than using <code>free</code> directly, so as to allow accurate record
  96. keeping.
  97. </p></dd></dl>
  98. <dl>
  99. <dt><a name="index-avm_005finitialize_005fportals"></a><u>Function:</u> void <b>avm_initialize_portals</b><i> ()</i></dt>
  100. <dd><p>This function should be called by a client program prior to calling
  101. either of the above memory management functions in order to initialize
  102. some local variables. Anomalous results are possible otherwise.
  103. </p></dd></dl>
  104. <dl>
  105. <dt><a name="index-avm_005fcount_005fportals"></a><u>Function:</u> void <b>avm_count_portals</b><i> ()</i></dt>
  106. <dd><p>This function should be called at the end of a run or after the last
  107. call to any of the other functions in this section as a way of detecting
  108. memory leaks associated with <code>portal</code> pointers. A warning message
  109. will be written to standard error if any remains unreclaimed.
  110. </p></dd></dl>
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