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diff --git a/erts/doc/src/atomics.xml b/erts/doc/src/atomics.xml new file mode 100644 index 0000000000..455973f011 --- /dev/null +++ b/erts/doc/src/atomics.xml @@ -0,0 +1,185 @@ +<?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 since="OTP 21.2">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 following 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" since="OTP 21.2"/> + <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> + <p>Atomics are not tied to the current process and are automatically + garbage collected when they are no longer referenced.</p> + </desc> + </func> + + <func> + <name name="put" arity="3" since="OTP 21.2"/> + <fsummary>Set atomic value</fsummary> + <desc> + <p>Set atomic to <c><anno>Value</anno></c>.</p> + </desc> + </func> + + <func> + <name name="get" arity="2" since="OTP 21.2"/> + <fsummary>Read atomic value</fsummary> + <desc> + <p>Read atomic value.</p> + </desc> + </func> + + <func> + <name name="add" arity="3" since="OTP 21.2"/> + <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" since="OTP 21.2"/> + <fsummary>Atomic add and get</fsummary> + <desc> + <p>Atomic addition and return of the result.</p> + </desc> + </func> + + <func> + <name name="sub" arity="3" since="OTP 21.2"/> + <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" since="OTP 21.2"/> + <fsummary>Atomic sub and get</fsummary> + <desc> + <p>Atomic subtraction and return of the result.</p> + </desc> + </func> + + <func> + <name name="exchange" arity="3" since="OTP 21.2"/> + <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" since="OTP 21.2"/> + <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" since="OTP 21.2"/> + <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> |