136 lines
4.5 KiB
HTML
136 lines
4.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>Return values from thread start routines are not integers</title>
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<!-- RCHVMW2 on 29 Jan 1999 at 10:01:37 -->
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<!--File Edited November 2001 -->
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<!--End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>Return values from thread start routines are not integers</h2>
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<p>Return values from a thread are defined to be of type <strong>void
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*</strong>. On some platforms, a void * and an integer can be easily
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interchanged with no loss of information. Until Version 4 Release 2, this was
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not true on the iSeries. The iSeries enforces stricter pointer rules to both
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prevent and detect application bugs or a malicious program's behavior. Thus,
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when converting integers to pointers by a mechanism not directly supported by
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your compiler, the valid pointer information is lost, and the pointer is always
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set to <strong>NULL</strong> (regardless of its binary value).</p>
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<p>New support put into the system in Version 4 Release 2 allows you to store
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an integer into a pointer, and still have the pointer be
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non-<strong>NULL</strong>. You cannot store to, read from, or defer a pointer
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created by this mechanism, but the pointer appears
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non-<strong>NULL</strong>.</p>
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<p>The macros <strong>__INT</strong>() and <strong>__VOID</strong>() are
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provided to aid in compatibility and allow you to easily store and retrieve
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integer information in pointer variables even if your compiler does not support
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the direct typecast. These macros allow explicit conversion from a pointer to
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an integer and from an integer to a pointer.</p>
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<p><strong>Note:</strong> The macros <strong>__INT</strong>() and <strong>
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__VOID</strong>() result in function calls.</p>
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<br>
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<h3>Example</h3>
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<p>The following example shows the correct way to store and retrieve integer
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information in pointer variables.</p>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<pre>
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#define _MULTI_THREADED
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#include <pthread.h>
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#include <stdio.h>
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#include "check.h"
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int main(int argc, char **argv)
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{
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void *status1 = __VOID(5);
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void *status2 = __VOID(999);
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if (status1 == NULL) {
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printf("Status1 pointer is NULL\n");
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}
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else {
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printf("Status1 pointer is non-NULL\n");
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}
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if (status1 == status2) {
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printf("Both status variables as pointers are equal\n");
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}
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else {
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if (status1 < status2) {
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printf("Status1 is greater than status2\n");
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}
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else {
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if (status1 < status2) {
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printf("Status1 is less then status2\n");
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}
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else {
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printf("The pointers are unordered!\n");
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}
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}
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}
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printf("Pointer values stored in status variables are:\n"
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" status1 = %.8x %.8x %.8x %.8x\n"
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" status2 = %.8x %.8x %.8x %.8x\n",
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status1, status2);
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printf("Integer values stored in status variables are:\n"
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" status1 = %d\n"
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" status2 = %d\n",
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__INT(status1), __INT(status2));
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return;
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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Status1 pointer is non-NULL
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Status1 is less then status2
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Pointer values stored in status variables are:
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status1 = 80000000 00000000 00008302 00000005
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status2 = 80000000 00000000 00008302 000003e7
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Integer values stored in status variables are:
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status1 = 5
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status2 = 999
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</pre>
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center">
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<a href="#Top_Of_Page">Top</a> |
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<a href="rzah4mst.htm">Pthread APIs</a> |
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<a href="aplist.htm">APIs by category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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