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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_subtract</h1>
<p>Atomically subtract a value from some data item in FAM.</p>
<h2>Synopsis</h2>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
int32_t value);</p>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
int64_t value);</p>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
uint32_t value);</p>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
uint64_t value);</p>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
float value);</p>
<p class="code">void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset,
double value);</p>
<h2>Description</h2>
<p>These methods atomically subtract a value from an existing value
in FAM.</p>
<h2>Input Arguments</h2>
<table>
<tbody>
<tr>
<th>
Name
</th>
<th>
Description
</th>
</tr>
<tr>
<td class="code">
descriptor
</td>
<td>
Descriptor associated with the data item.
</td>
</tr>
<tr>
<td class="code">
offset
</td>
<td>
Offset within the data item in FAM where value is located.
</td>
</tr>
<tr>
<td class="code">
value
</td>
<td>
Value to be subtracted from the existing value at the given
location.
</td>
</tr>
</tbody>
</table>
<h2>Return Values</h2>
<p>None. 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>
</tbody></table>
<h2>Notes</h2>
<p>These methods atomically subtract a value to an existing value in
FAM, and return before the operation is complete. 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.</p>
<p>Successful completion of a subsequent <code>fam_quiet()</code> call ensures the completion of this atomic operation.</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
// (an integer array with at least 10 elements)
Fam_Descriptor *descriptor = myFam->fam_lookup("myItem", "myRegion");
//Atomically subtract a value of 50 from the first integer element in the array
myFam->fam_subtract(descriptor, 0, 50);
// ensure that the subtract operation is complete
myFam->fam_quiet();
// The first integer in FAM is now subtracted with a value of 50
} 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>