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authorSverker Eriksson <[email protected]>2018-11-15 15:24:32 +0100
committerSverker Eriksson <[email protected]>2018-11-15 15:24:32 +0100
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erts: Add new module 'atomics'
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+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE erlref SYSTEM "erlref.dtd">
+
+<erlref>
+ <header>
+ <copyright>
+ <year>2018</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ </legalnotice>
+
+ <title>atomics</title>
+ </header>
+ <module>atomics</module>
+ <modulesummary>Atomic Functions</modulesummary>
+ <description>
+ <p>This module provides a set of functions to do atomic operations towards
+ mutable atomic variables. The implementation utilizes only
+ atomic hardware instructions without any software level locking, which makes
+ it very efficient for concurrent access. The atomics are organized into
+ arrays with the follwing semantics:</p>
+ <list type="bulleted">
+ <item>
+ <p>Atomics are 64 bit integers.</p>
+ </item>
+ <item>
+ <p>Atomics can be represented as either signed or unsigned.</p>
+ </item>
+ <item>
+ <p>Atomics wrap around at overflow and underflow operations.</p>
+ </item>
+ <item>
+ <p>All operations guarantee atomicity. No intermediate results can be
+ seen. The result of one mutation can only be the input to one
+ following mutation.</p>
+ </item>
+ <item>
+ <p>All atomic operations are mutually ordered. If atomic B is updated
+ <em>after</em> atomic A, then that is how it will appear to any
+ concurrent readers. No one can read the new value of B and then read the
+ old value of A.</p>
+ </item>
+ <item>
+ <p>Indexes into atomic arrays are one-based. An atomic array of
+ arity N contains N atomics with index from 1 to N.</p>
+ </item>
+ </list>
+ </description>
+
+ <datatypes>
+ <datatype>
+ <name name="atomics_ref"/>
+ <desc><p>Identifies an atomic array returned from
+ <seealso marker="#new/2"><c>new/2</c></seealso>.</p>
+ </desc>
+ </datatype>
+ </datatypes>
+
+ <funcs>
+ <func>
+ <name name="new" arity="2"/>
+ <fsummary>Create atomic array</fsummary>
+ <desc>
+ <p>Create a new atomic array of <c><anno>Arity</anno></c> atomics.</p>
+ <p>Argument <c><anno>Opts</anno></c> is a list of the following possible
+ options:</p>
+ <taglist>
+ <tag><c>{signed, boolean()}</c></tag>
+ <item><p>Indicate if the elements of the array will be treated
+ as signed or unsigned integers. Default is <c>true</c> (signed).</p>
+ <p>The integer interval for signed atomics are from <c>-(1 bsl 63)</c>
+ to <c>(1 bsl 63)-1</c> and for unsigned atomics from <c>0</c> to <c>(1
+ bsl 64)-1</c>.</p>
+ </item>
+ </taglist>
+ </desc>
+ </func>
+
+ <func>
+ <name name="put" arity="3"/>
+ <fsummary>Set atomic value</fsummary>
+ <desc>
+ <p>Set atomic to <c><anno>Value</anno></c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="get" arity="2"/>
+ <fsummary>Read atomic value</fsummary>
+ <desc>
+ <p>Read atomic value.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="add" arity="3"/>
+ <fsummary>Add to atomic</fsummary>
+ <desc>
+ <p>Add <c><anno>Incr</anno></c> to atomic.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="add_get" arity="3"/>
+ <fsummary>Atomic add and get</fsummary>
+ <desc>
+ <p>Atomic addition and return of the result.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="sub" arity="3"/>
+ <fsummary>Subtract from atomic</fsummary>
+ <desc>
+ <p>Subtract <c><anno>Decr</anno></c> from atomic.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="sub_get" arity="3"/>
+ <fsummary>Atomic sub and get</fsummary>
+ <desc>
+ <p>Atomic subtraction and return of the result.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="exchange" arity="3"/>
+ <fsummary>Atomic exchange.</fsummary>
+ <desc>
+ <p>Atomically replaces the value of the atomic with
+ <c><anno>Desired</anno></c> and returns the value it held
+ previously.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="compare_exchange" arity="4"/>
+ <fsummary>Atomic compare and exchange.</fsummary>
+ <desc>
+ <p>Atomically compares the atomic with <c><anno>Expected</anno></c>,
+ and if those are equal, set atomic to <c><anno>Desired</anno></c>.
+ Returns <c>ok</c> if <c><anno>Desired</anno></c> was written. Returns
+ the actual atomic value if not equal to <c><anno>Expected</anno></c>.</p>
+ </desc>
+ </func>
+
+ <func>
+ <name name="info" arity="1"/>
+ <fsummary>Get information about atomic array.</fsummary>
+ <desc>
+ <p>Return information about an atomic array in a map. The map
+ has the following keys:</p>
+ <taglist>
+ <tag><c>size</c></tag>
+ <item><p>The number of atomics in the array.</p></item>
+ <tag><c>max</c></tag>
+ <item><p>The highest possible value an atomic in this array can
+ hold.</p></item>
+ <tag><c>min</c></tag>
+ <item><p>The lowest possible value an atomic in this array can
+ hold.</p></item>
+ <tag><c>memory</c></tag>
+ <item><p>Approximate memory consumption for the array in
+ bytes.</p></item>
+ </taglist>
+ </desc>
+ </func>
+
+ </funcs>
+</erlref>