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<!DOCTYPE html>
<html lang="en">
<head>
<link rel="stylesheet" type="text/css" href="styles/style.css">
<title>OpenFAM: A library for programming Fabric-Attached Memory</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<header>
<h1>OpenFAM Reference Implementation</h1>
</header>
<section>
<nav>
<ul>
<li><a href="index.html">Home</a></li>
<li><a href="release_notes.html">Release Notes</a></li>
<li><a href="limitations.html">Design Choices</a></li>
<li><a href="errors.html">Exceptions and Error Codes</a></li>
<li><a href="services.html">Services</a></li>
<li><a href="config_files.html">Configuration Files</a></li>
</ul>
<hr>
Initialization and Finalization
<ul>
<li><a href="fam_initialize.html">fam_initialize</a></li>
<li><a href="fam_finalize.html">fam_finalize</a></li>
<li><a href="fam_abort.html">fam_abort</a></li>
</ul>
<hr>
Options & Query
<ul>
<li><a href="fam_list_options.html">fam_list_options</a></li>
<li><a href="fam_get_option.html">fam_get_option</a></li>
<li><a href="fam_lookup.html">fam_lookup</a></li>
<li><a href="fam_stat.html">fam_stat</a></li>
</ul>
<hr>
Memory Allocation
<ul>
<li><a href="fam_create_region.html">fam_create_region</a></li>
<li><a href="fam_destroy_region.html">fam_destroy_region</a></li>
<li><a href="fam_resize_region.html">fam_resize_region</a></li>
<li><a href="fam_allocate.html">fam_allocate</a></li>
<li><a href="fam_deallocate.html">fam_deallocate</a></li>
<li><a href="fam_change_permissions.html">fam_change_permissions</a></li>
<li><a href="fam_close.html">fam_close</a></li>
</ul>
<hr>
Memory Map
<ul>
<li><a href="fam_map.html">fam_map</a></li>
<li><a href="fam_unmap.html">fam_unmap</a></li>
</ul>
<hr>
Data Path Operations
<ul>
<li><a href="fam_get.html">fam_get</a></li>
<li><a href="fam_put.html">fam_put</a></li>
<li><a href="fam_gather.html">fam_gather</a></li>
<li><a href="fam_scatter.html">fam_scatter</a></li>
<li><a href="fam_copy.html">fam_copy</a></li>
<li><a href="fam_copy_wait.html">fam_copy_wait</a></li>
<li><a href="fam_backup.html">fam_backup</a></li>
<li><a href="fam_backup_wait.html">fam_backup_wait</a></li>
<li><a href="fam_restore.html">fam_restore</a></li>
<li><a href="fam_restore_wait.html">fam_restore_wait</a></li>
<li><a href="fam_delete_backup.html">fam_delete_backup</a></li>
<li><a href="fam_delete_backup_wait.html">fam_delete_backup_wait</a></li>
</ul>
<hr>
Atomics
<ul>
<li><a href="fam_set.html">fam_set</a></li>
<li><a href="fam_add.html">fam_add</a></li>
<li><a href="fam_subtract.html">fam_subtract</a></li>
<li><a href="fam_min.html">fam_min</a></li>
<li><a href="fam_max.html">fam_max</a></li>
<li><a href="fam_and.html">fam_and</a></li>
<li><a href="fam_or.html">fam_or</a></li>
<li><a href="fam_xor.html">fam_xor</a></li>
<li><a href="fam_fetch_TYPE.html">fam_fetch_TYPE</a></li>
<li><a href="fam_swap.html">fam_swap</a></li>
<li><a href="fam_compare_swap.html">fam_compare_swap</a></li>
<li><a href="fam_fetch_add.html">fam_fetch_add</a></li>
<li><a href="fam_fetch_subtract.html">fam_fetch_subtract</a></li>
<li><a href="fam_fetch_min.html">fam_fetch_min</a></li>
<li><a href="fam_fetch_and.html">fam_fetch_and</a></li>
<li><a href="fam_fetch_max.html">fam_fetch_max</a></li>
<li><a href="fam_fetch_or.html">fam_fetch_or</a></li>
<li><a href="fam_fetch_xor.html">fam_fetch_xor</a></li>
</ul>
<hr>
Ordering
<ul>
<li><a href="fam_barrier_all.html">fam_barrier_all</a></li>
<li><a href="fam_fence.html">fam_fence</a></li>
<li><a href="fam_quiet.html">fam_quiet</a></li>
<li><a href="fam_progress.html">fam_progress</a></li>
<li><a href="fam_context_open.html">fam_context_open</a></li>
<li><a href="fam_context_close.html">fam_context_close</a></li>
</ul>
<hr>
</nav>
<article>
<h1 class="code">openfam::fam::fam_compare_swap</h1>
<p>Atomically conditionally replace a value in FAM with the given
value and return the old value.</p>
<h2>Synopsis</h2>
<p class="code">int32_t fam_compare_swap(Fam_Descriptor *descriptor, uint64_t
offset, int32_t oldValue, int32_t newValue);</p>
<p class="code">int64_t fam_compare_swap(Fam_Descriptor *descriptor, uint64_t
offset, int64_t oldValue, int64_t newValue);</p>
<p class="code">uint32_t fam_compare_swap(Fam_Descriptor *descriptor, uint64_t
offset, uint32_t oldValue, uint32_t newValue);</p>
<p class="code">uint64_t fam_compare_swap(Fam_Descriptor *descriptor, uint64_t
offset, uint64_t oldValue, uint64_t newValue);</p>
<p class="code">int128_t fam_compare_swap(Fam_Descriptor *descriptor, uint64_t
offset, int128_t oldValue, int128_t newValue);</p>
<h2>Description</h2>
<p>These methods atomically perform a compare and swap of a value
in FAM, and return the old value from FAM. All of these methods
atomically implement the following algorithm (where TYPE is one of the
data types listed in the synopsis):</p>
<pre>
TYPE cas(TYPE *p, TYPE oldValue, TYPE newValue){
if(*p != oldValue){
return *p;
} else {
*p = newValue;
return oldValue;
}
}
</pre>
<h2>Input Arguments</h2>
<table>
<tbody>
<tr>
<th>
Name
</th>
<th>
Description
</th>
</tr>
<tr>
<td>
descriptor
</td>
<td>
Descriptor associated with the data item.
</td>
</tr>
<tr>
<td>
offset
</td>
<td>
Offset within the data item in FAM where
value is located.
</td>
</tr>
<tr>
<td>
oldValue
</td>
<td>
Expected old value at the FAM location.
</td>
</tr>
<tr>
<td>
newValue
</td>
<td>
New value to use if successful.
</td>
</tr>
</tbody>
</table>
<h2>Return Values</h2>
<p>The old value from FAM. Throws <code>Fam_Exception</code> on
error.</p>
<h2>Fam error numbers</h2>
<table><tbody>
<tr><th>Error</th><th>Description</th></tr>
<tr><td class="code">FAM_ERR_INVALID</td><td>API called with incorrect parameters.</td></tr>
<tr><td class="code">FAM_ERR_NOPERM</td><td>Caller does not have access rights.</td></tr>
<tr><td class="code">FAM_ERR_LIBFABRIC</td><td>Libfabric error occurred.</td></tr>
<tr><td class="code">FAM_ERR_NOTFOUND</td><td>Item not found in the region.</td></tr>
<tr><td class="code">FAM_ERR_RPC</td><td>Communication error from grpc layer.</td></tr>
<tr><td class="code">FAM_ERR_RPC_CLIENT_NOTFOUND</td><td>RPC service not available.</td></tr>
<tr><td class="code">FAM_ERR_METADATA</td><td>Metadata service error.</td></tr>
<tr><td class="code">FAM_ERR_MEMORY</td><td>Memory service error.</td></tr>
<tr><td class="code">FAM_ERR_RESOURCE</td><td>Resource not available.</td></tr>
<tr><td class="code">FAM_ERR_TIMEOUT</td><td>Number of libfabric retry count reached</td></tr>
</tbody></table>
<h2>Notes</h2>
<p>These methods atomically compare a value in
FAM with an expected value and if the value in FAM is equal to the
expected value, swap a new value. The old value is returned. Note that
the offset argument must point to the correct value for the data type.
Availability of these methods is dependent on hardware support for the
operations. GCC currently does not define <code>int128_t</code>; it is defined in
<code>fam.h</code>.</p>
<h2>Example</h2>
<pre>
#include <string.h>
#include <fam/fam.h>
#include <fam/fam_exception.h>
using namespace std;
using namespace openfam;
int main(void) {
fam *myFam = new fam();
// ... Initialization code here
try {
// look up the descriptor to a previously allocated data item
Fam_Descriptor *descriptor = myFam->fam_lookup("myItem", "myRegion");
// Atomically compare and replaces the first integer element in FAM with 0
// only if it contains 100; It returns the old value
int32_t oldValue = myFam->fam_compare_swap(descriptor, 0, 100, 0);
// The first integer in FAM is replaced with 0 only if it contains 100;
// Old value is returned
printf("Old value of first integer element in FAM: %d\n", oldValue);
// ... subsequent code here
} catch (Fam_Exception &e) {
printf("fam API failed: %d: %s\n", e.fam_error(), e.fam_error_msg());
}
// ... Finalization code follows
}
</pre>
</article>
</section>
<footer>
<p>Copyright 2021-23, Hewlett Packard Enterprise Development Co, LLP</p>
</footer>
</body>
</html>