693 lines
41 KiB
HTML
693 lines
41 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<!--[if IE]><meta http-equiv="X-UA-Compatible" content="IE=edge"><![endif]-->
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta name="generator" content="Asciidoctor 1.5.8">
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<title>Use of index and Racy Git problem</title>
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<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700">
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<style>
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/* Asciidoctor default stylesheet | MIT License | http://asciidoctor.org */
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/* Uncomment @import statement below to use as custom stylesheet */
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/*@import "https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700";*/
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article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section,summary{display:block}
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audio,canvas,video{display:inline-block}
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audio:not([controls]){display:none;height:0}
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script{display:none!important}
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html{font-family:sans-serif;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%}
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a{background:transparent}
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a:focus{outline:thin dotted}
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a:active,a:hover{outline:0}
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h1{font-size:2em;margin:.67em 0}
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abbr[title]{border-bottom:1px dotted}
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b,strong{font-weight:bold}
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dfn{font-style:italic}
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hr{-moz-box-sizing:content-box;box-sizing:content-box;height:0}
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mark{background:#ff0;color:#000}
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code,kbd,pre,samp{font-family:monospace;font-size:1em}
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pre{white-space:pre-wrap}
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q{quotes:"\201C" "\201D" "\2018" "\2019"}
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small{font-size:80%}
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sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline}
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sup{top:-.5em}
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sub{bottom:-.25em}
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img{border:0}
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svg:not(:root){overflow:hidden}
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figure{margin:0}
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fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em}
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legend{border:0;padding:0}
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button,input,select,textarea{font-family:inherit;font-size:100%;margin:0}
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button,input{line-height:normal}
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button,select{text-transform:none}
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button,html input[type="button"],input[type="reset"],input[type="submit"]{-webkit-appearance:button;cursor:pointer}
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button[disabled],html input[disabled]{cursor:default}
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input[type="checkbox"],input[type="radio"]{box-sizing:border-box;padding:0}
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button::-moz-focus-inner,input::-moz-focus-inner{border:0;padding:0}
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textarea{overflow:auto;vertical-align:top}
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table{border-collapse:collapse;border-spacing:0}
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*,*::before,*::after{-moz-box-sizing:border-box;-webkit-box-sizing:border-box;box-sizing:border-box}
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html,body{font-size:100%}
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body{background:#fff;color:rgba(0,0,0,.8);padding:0;margin:0;font-family:"Noto Serif","DejaVu Serif",serif;font-weight:400;font-style:normal;line-height:1;position:relative;cursor:auto;tab-size:4;-moz-osx-font-smoothing:grayscale;-webkit-font-smoothing:antialiased}
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a:hover{cursor:pointer}
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img,object,embed{max-width:100%;height:auto}
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object,embed{height:100%}
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img{-ms-interpolation-mode:bicubic}
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.left{float:left!important}
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.right{float:right!important}
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.text-left{text-align:left!important}
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.text-right{text-align:right!important}
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.text-center{text-align:center!important}
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.text-justify{text-align:justify!important}
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.hide{display:none}
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img,object,svg{display:inline-block;vertical-align:middle}
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textarea{height:auto;min-height:50px}
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select{width:100%}
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.center{margin-left:auto;margin-right:auto}
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.stretch{width:100%}
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.subheader,.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{line-height:1.45;color:#7a2518;font-weight:400;margin-top:0;margin-bottom:.25em}
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div,dl,dt,dd,ul,ol,li,h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6,pre,form,p,blockquote,th,td{margin:0;padding:0;direction:ltr}
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a{color:#2156a5;text-decoration:underline;line-height:inherit}
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a:hover,a:focus{color:#1d4b8f}
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a img{border:none}
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p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
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p aside{font-size:.875em;line-height:1.35;font-style:italic}
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h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Open Sans","DejaVu Sans",sans-serif;font-weight:300;font-style:normal;color:#ba3925;text-rendering:optimizeLegibility;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
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h1 small,h2 small,h3 small,#toctitle small,.sidebarblock>.content>.title small,h4 small,h5 small,h6 small{font-size:60%;color:#e99b8f;line-height:0}
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h1{font-size:2.125em}
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h2{font-size:1.6875em}
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h3,#toctitle,.sidebarblock>.content>.title{font-size:1.375em}
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h4,h5{font-size:1.125em}
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h6{font-size:1em}
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hr{border:solid #dddddf;border-width:1px 0 0;clear:both;margin:1.25em 0 1.1875em;height:0}
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em,i{font-style:italic;line-height:inherit}
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strong,b{font-weight:bold;line-height:inherit}
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small{font-size:60%;line-height:inherit}
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code{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;color:rgba(0,0,0,.9)}
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ul,ol,dl{font-size:1em;line-height:1.6;margin-bottom:1.25em;list-style-position:outside;font-family:inherit}
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ul,ol{margin-left:1.5em}
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ul li ul,ul li ol{margin-left:1.25em;margin-bottom:0;font-size:1em}
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ul.square li ul,ul.circle li ul,ul.disc li ul{list-style:inherit}
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ul.square{list-style-type:square}
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ul.circle{list-style-type:circle}
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ul.disc{list-style-type:disc}
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ol li ul,ol li ol{margin-left:1.25em;margin-bottom:0}
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dl dt{margin-bottom:.3125em;font-weight:bold}
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dl dd{margin-bottom:1.25em}
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abbr,acronym{text-transform:uppercase;font-size:90%;color:rgba(0,0,0,.8);border-bottom:1px dotted #ddd;cursor:help}
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abbr{text-transform:none}
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blockquote{margin:0 0 1.25em;padding:.5625em 1.25em 0 1.1875em;border-left:1px solid #ddd}
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blockquote cite{display:block;font-size:.9375em;color:rgba(0,0,0,.6)}
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blockquote cite::before{content:"\2014 \0020"}
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blockquote cite a,blockquote cite a:visited{color:rgba(0,0,0,.6)}
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blockquote,blockquote p{line-height:1.6;color:rgba(0,0,0,.85)}
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@media screen and (min-width:768px){h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2}
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h1{font-size:2.75em}
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h2{font-size:2.3125em}
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h3,#toctitle,.sidebarblock>.content>.title{font-size:1.6875em}
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h4{font-size:1.4375em}}
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table{background:#fff;margin-bottom:1.25em;border:solid 1px #dedede}
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table thead,table tfoot{background:#f7f8f7}
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table thead tr th,table thead tr td,table tfoot tr th,table tfoot tr td{padding:.5em .625em .625em;font-size:inherit;color:rgba(0,0,0,.8);text-align:left}
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table tr th,table tr td{padding:.5625em .625em;font-size:inherit;color:rgba(0,0,0,.8)}
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table tr.even,table tr.alt,table tr:nth-of-type(even){background:#f8f8f7}
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table thead tr th,table tfoot tr th,table tbody tr td,table tr td,table tfoot tr td{display:table-cell;line-height:1.6}
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h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2;word-spacing:-.05em}
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h1 strong,h2 strong,h3 strong,#toctitle strong,.sidebarblock>.content>.title strong,h4 strong,h5 strong,h6 strong{font-weight:400}
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.clearfix::before,.clearfix::after,.float-group::before,.float-group::after{content:" ";display:table}
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.clearfix::after,.float-group::after{clear:both}
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*:not(pre)>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background-color:#f7f7f8;-webkit-border-radius:4px;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed;word-wrap:break-word}
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*:not(pre)>code.nobreak{word-wrap:normal}
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*:not(pre)>code.nowrap{white-space:nowrap}
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pre,pre>code{line-height:1.45;color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;text-rendering:optimizeSpeed}
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em em{font-style:normal}
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strong strong{font-weight:400}
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.keyseq{color:rgba(51,51,51,.8)}
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kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background-color:#f7f7f7;border:1px solid #ccc;-webkit-border-radius:3px;border-radius:3px;-webkit-box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em white inset;box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em #fff inset;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
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.keyseq kbd:first-child{margin-left:0}
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.keyseq kbd:last-child{margin-right:0}
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.menuseq,.menuref{color:#000}
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.menuseq b:not(.caret),.menuref{font-weight:inherit}
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.menuseq{word-spacing:-.02em}
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.menuseq b.caret{font-size:1.25em;line-height:.8}
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.menuseq i.caret{font-weight:bold;text-align:center;width:.45em}
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b.button::before,b.button::after{position:relative;top:-1px;font-weight:400}
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b.button::before{content:"[";padding:0 3px 0 2px}
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b.button::after{content:"]";padding:0 2px 0 3px}
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p a>code:hover{color:rgba(0,0,0,.9)}
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#header,#content,#footnotes,#footer{width:100%;margin-left:auto;margin-right:auto;margin-top:0;margin-bottom:0;max-width:62.5em;*zoom:1;position:relative;padding-left:.9375em;padding-right:.9375em}
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#header::before,#header::after,#content::before,#content::after,#footnotes::before,#footnotes::after,#footer::before,#footer::after{content:" ";display:table}
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#header::after,#content::after,#footnotes::after,#footer::after{clear:both}
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#content{margin-top:1.25em}
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#content::before{content:none}
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#header>h1:first-child{color:rgba(0,0,0,.85);margin-top:2.25rem;margin-bottom:0}
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#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #dddddf}
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#header>h1:only-child,body.toc2 #header>h1:nth-last-child(2){border-bottom:1px solid #dddddf;padding-bottom:8px}
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#header .details{border-bottom:1px solid #dddddf;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:-ms-flexbox;display:-webkit-flex;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap}
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#header .details span:first-child{margin-left:-.125em}
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#header .details span.email a{color:rgba(0,0,0,.85)}
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#header .details br{display:none}
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#header .details br+span::before{content:"\00a0\2013\00a0"}
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#header .details br+span.author::before{content:"\00a0\22c5\00a0";color:rgba(0,0,0,.85)}
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#header .details br+span#revremark::before{content:"\00a0|\00a0"}
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#header #revnumber{text-transform:capitalize}
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#header #revnumber::after{content:"\00a0"}
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#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #dddddf;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
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#toc{border-bottom:1px solid #e7e7e9;padding-bottom:.5em}
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#toc>ul{margin-left:.125em}
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#toc ul.sectlevel0>li>a{font-style:italic}
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#toc ul.sectlevel0 ul.sectlevel1{margin:.5em 0}
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#toc ul{font-family:"Open Sans","DejaVu Sans",sans-serif;list-style-type:none}
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#toc li{line-height:1.3334;margin-top:.3334em}
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#toc a{text-decoration:none}
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#toc a:active{text-decoration:underline}
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#toctitle{color:#7a2518;font-size:1.2em}
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@media screen and (min-width:768px){#toctitle{font-size:1.375em}
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body.toc2{padding-left:15em;padding-right:0}
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#toc.toc2{margin-top:0!important;background-color:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #e7e7e9;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
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#toc.toc2 #toctitle{margin-top:0;margin-bottom:.8rem;font-size:1.2em}
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#toc.toc2>ul{font-size:.9em;margin-bottom:0}
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#toc.toc2 ul ul{margin-left:0;padding-left:1em}
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#toc.toc2 ul.sectlevel0 ul.sectlevel1{padding-left:0;margin-top:.5em;margin-bottom:.5em}
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body.toc2.toc-right{padding-left:0;padding-right:15em}
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body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #e7e7e9;left:auto;right:0}}
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@media screen and (min-width:1280px){body.toc2{padding-left:20em;padding-right:0}
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#toc.toc2{width:20em}
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#toc.toc2 #toctitle{font-size:1.375em}
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#toc.toc2>ul{font-size:.95em}
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#toc.toc2 ul ul{padding-left:1.25em}
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body.toc2.toc-right{padding-left:0;padding-right:20em}}
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#content #toc{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
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#content #toc>:first-child{margin-top:0}
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#content #toc>:last-child{margin-bottom:0}
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#footer{max-width:100%;background-color:rgba(0,0,0,.8);padding:1.25em}
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#footer-text{color:rgba(255,255,255,.8);line-height:1.44}
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#content{margin-bottom:.625em}
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.sect1{padding-bottom:.625em}
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@media screen and (min-width:768px){#content{margin-bottom:1.25em}
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.sect1{padding-bottom:1.25em}}
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.sect1:last-child{padding-bottom:0}
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.sect1+.sect1{border-top:1px solid #e7e7e9}
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#content h1>a.anchor,h2>a.anchor,h3>a.anchor,#toctitle>a.anchor,.sidebarblock>.content>.title>a.anchor,h4>a.anchor,h5>a.anchor,h6>a.anchor{position:absolute;z-index:1001;width:1.5ex;margin-left:-1.5ex;display:block;text-decoration:none!important;visibility:hidden;text-align:center;font-weight:400}
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#content h1>a.anchor::before,h2>a.anchor::before,h3>a.anchor::before,#toctitle>a.anchor::before,.sidebarblock>.content>.title>a.anchor::before,h4>a.anchor::before,h5>a.anchor::before,h6>a.anchor::before{content:"\00A7";font-size:.85em;display:block;padding-top:.1em}
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#content h1:hover>a.anchor,#content h1>a.anchor:hover,h2:hover>a.anchor,h2>a.anchor:hover,h3:hover>a.anchor,#toctitle:hover>a.anchor,.sidebarblock>.content>.title:hover>a.anchor,h3>a.anchor:hover,#toctitle>a.anchor:hover,.sidebarblock>.content>.title>a.anchor:hover,h4:hover>a.anchor,h4>a.anchor:hover,h5:hover>a.anchor,h5>a.anchor:hover,h6:hover>a.anchor,h6>a.anchor:hover{visibility:visible}
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#content h1>a.link,h2>a.link,h3>a.link,#toctitle>a.link,.sidebarblock>.content>.title>a.link,h4>a.link,h5>a.link,h6>a.link{color:#ba3925;text-decoration:none}
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#content h1>a.link:hover,h2>a.link:hover,h3>a.link:hover,#toctitle>a.link:hover,.sidebarblock>.content>.title>a.link:hover,h4>a.link:hover,h5>a.link:hover,h6>a.link:hover{color:#a53221}
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.audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
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.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{text-rendering:optimizeLegibility;text-align:left;font-family:"Noto Serif","DejaVu Serif",serif;font-size:1rem;font-style:italic}
|
||
|
|
table.tableblock.fit-content>caption.title{white-space:nowrap;width:0}
|
||
|
|
.paragraph.lead>p,#preamble>.sectionbody>[class="paragraph"]:first-of-type p{font-size:1.21875em;line-height:1.6;color:rgba(0,0,0,.85)}
|
||
|
|
table.tableblock #preamble>.sectionbody>[class="paragraph"]:first-of-type p{font-size:inherit}
|
||
|
|
.admonitionblock>table{border-collapse:separate;border:0;background:none;width:100%}
|
||
|
|
.admonitionblock>table td.icon{text-align:center;width:80px}
|
||
|
|
.admonitionblock>table td.icon img{max-width:none}
|
||
|
|
.admonitionblock>table td.icon .title{font-weight:bold;font-family:"Open Sans","DejaVu Sans",sans-serif;text-transform:uppercase}
|
||
|
|
.admonitionblock>table td.content{padding-left:1.125em;padding-right:1.25em;border-left:1px solid #dddddf;color:rgba(0,0,0,.6)}
|
||
|
|
.admonitionblock>table td.content>:last-child>:last-child{margin-bottom:0}
|
||
|
|
.exampleblock>.content{border-style:solid;border-width:1px;border-color:#e6e6e6;margin-bottom:1.25em;padding:1.25em;background:#fff;-webkit-border-radius:4px;border-radius:4px}
|
||
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.exampleblock>.content>:first-child{margin-top:0}
|
||
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|
.exampleblock>.content>:last-child{margin-bottom:0}
|
||
|
|
.sidebarblock{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
|
||
|
|
.sidebarblock>:first-child{margin-top:0}
|
||
|
|
.sidebarblock>:last-child{margin-bottom:0}
|
||
|
|
.sidebarblock>.content>.title{color:#7a2518;margin-top:0;text-align:center}
|
||
|
|
.exampleblock>.content>:last-child>:last-child,.exampleblock>.content .olist>ol>li:last-child>:last-child,.exampleblock>.content .ulist>ul>li:last-child>:last-child,.exampleblock>.content .qlist>ol>li:last-child>:last-child,.sidebarblock>.content>:last-child>:last-child,.sidebarblock>.content .olist>ol>li:last-child>:last-child,.sidebarblock>.content .ulist>ul>li:last-child>:last-child,.sidebarblock>.content .qlist>ol>li:last-child>:last-child{margin-bottom:0}
|
||
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.literalblock pre,.listingblock pre:not(.highlight),.listingblock pre[class="highlight"],.listingblock pre[class^="highlight "],.listingblock pre.CodeRay,.listingblock pre.prettyprint{background:#f7f7f8}
|
||
|
|
.sidebarblock .literalblock pre,.sidebarblock .listingblock pre:not(.highlight),.sidebarblock .listingblock pre[class="highlight"],.sidebarblock .listingblock pre[class^="highlight "],.sidebarblock .listingblock pre.CodeRay,.sidebarblock .listingblock pre.prettyprint{background:#f2f1f1}
|
||
|
|
.literalblock pre,.literalblock pre[class],.listingblock pre,.listingblock pre[class]{-webkit-border-radius:4px;border-radius:4px;word-wrap:break-word;overflow-x:auto;padding:1em;font-size:.8125em}
|
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@media screen and (min-width:768px){.literalblock pre,.literalblock pre[class],.listingblock pre,.listingblock pre[class]{font-size:.90625em}}
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@media screen and (min-width:1280px){.literalblock pre,.literalblock pre[class],.listingblock pre,.listingblock pre[class]{font-size:1em}}
|
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.literalblock pre.nowrap,.literalblock pre.nowrap pre,.listingblock pre.nowrap,.listingblock pre.nowrap pre{white-space:pre;word-wrap:normal}
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.literalblock.output pre{color:#f7f7f8;background-color:rgba(0,0,0,.9)}
|
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.listingblock pre.highlightjs{padding:0}
|
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.listingblock pre.highlightjs>code{padding:1em;-webkit-border-radius:4px;border-radius:4px}
|
||
|
|
.listingblock pre.prettyprint{border-width:0}
|
||
|
|
.listingblock>.content{position:relative}
|
||
|
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.listingblock code[data-lang]::before{display:none;content:attr(data-lang);position:absolute;font-size:.75em;top:.425rem;right:.5rem;line-height:1;text-transform:uppercase;color:#999}
|
||
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.listingblock:hover code[data-lang]::before{display:block}
|
||
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.listingblock.terminal pre .command::before{content:attr(data-prompt);padding-right:.5em;color:#999}
|
||
|
|
.listingblock.terminal pre .command:not([data-prompt])::before{content:"$"}
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||
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table.pyhltable{border-collapse:separate;border:0;margin-bottom:0;background:none}
|
||
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table.pyhltable td{vertical-align:top;padding-top:0;padding-bottom:0;line-height:1.45}
|
||
|
|
table.pyhltable td.code{padding-left:.75em;padding-right:0}
|
||
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pre.pygments .lineno,table.pyhltable td:not(.code){color:#999;padding-left:0;padding-right:.5em;border-right:1px solid #dddddf}
|
||
|
|
pre.pygments .lineno{display:inline-block;margin-right:.25em}
|
||
|
|
table.pyhltable .linenodiv{background:none!important;padding-right:0!important}
|
||
|
|
.quoteblock{margin:0 1em 1.25em 1.5em;display:table}
|
||
|
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.quoteblock>.title{margin-left:-1.5em;margin-bottom:.75em}
|
||
|
|
.quoteblock blockquote,.quoteblock p{color:rgba(0,0,0,.85);font-size:1.15rem;line-height:1.75;word-spacing:.1em;letter-spacing:0;font-style:italic;text-align:justify}
|
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.quoteblock blockquote{margin:0;padding:0;border:0}
|
||
|
|
.quoteblock blockquote::before{content:"\201c";float:left;font-size:2.75em;font-weight:bold;line-height:.6em;margin-left:-.6em;color:#7a2518;text-shadow:0 1px 2px rgba(0,0,0,.1)}
|
||
|
|
.quoteblock blockquote>.paragraph:last-child p{margin-bottom:0}
|
||
|
|
.quoteblock .attribution{margin-top:.75em;margin-right:.5ex;text-align:right}
|
||
|
|
.verseblock{margin:0 1em 1.25em}
|
||
|
|
.verseblock pre{font-family:"Open Sans","DejaVu Sans",sans;font-size:1.15rem;color:rgba(0,0,0,.85);font-weight:300;text-rendering:optimizeLegibility}
|
||
|
|
.verseblock pre strong{font-weight:400}
|
||
|
|
.verseblock .attribution{margin-top:1.25rem;margin-left:.5ex}
|
||
|
|
.quoteblock .attribution,.verseblock .attribution{font-size:.9375em;line-height:1.45;font-style:italic}
|
||
|
|
.quoteblock .attribution br,.verseblock .attribution br{display:none}
|
||
|
|
.quoteblock .attribution cite,.verseblock .attribution cite{display:block;letter-spacing:-.025em;color:rgba(0,0,0,.6)}
|
||
|
|
.quoteblock.abstract blockquote::before,.quoteblock.excerpt blockquote::before,.quoteblock .quoteblock blockquote::before{display:none}
|
||
|
|
.quoteblock.abstract blockquote,.quoteblock.abstract p,.quoteblock.excerpt blockquote,.quoteblock.excerpt p,.quoteblock .quoteblock blockquote,.quoteblock .quoteblock p{line-height:1.6;word-spacing:0}
|
||
|
|
.quoteblock.abstract{margin:0 1em 1.25em;display:block}
|
||
|
|
.quoteblock.abstract>.title{margin:0 0 .375em;font-size:1.15em;text-align:center}
|
||
|
|
.quoteblock.excerpt,.quoteblock .quoteblock{margin:0 0 1.25em;padding:0 0 .25em 1em;border-left:.25em solid #dddddf}
|
||
|
|
.quoteblock.excerpt blockquote,.quoteblock.excerpt p,.quoteblock .quoteblock blockquote,.quoteblock .quoteblock p{color:inherit;font-size:1.0625rem}
|
||
|
|
.quoteblock.excerpt .attribution,.quoteblock .quoteblock .attribution{color:inherit;text-align:left;margin-right:0}
|
||
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|
table.tableblock{max-width:100%;border-collapse:separate}
|
||
|
|
p.tableblock:last-child{margin-bottom:0}
|
||
|
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td.tableblock>.content{margin-bottom:-1.25em}
|
||
|
|
table.tableblock,th.tableblock,td.tableblock{border:0 solid #dedede}
|
||
|
|
table.grid-all>thead>tr>.tableblock,table.grid-all>tbody>tr>.tableblock{border-width:0 1px 1px 0}
|
||
|
|
table.grid-all>tfoot>tr>.tableblock{border-width:1px 1px 0 0}
|
||
|
|
table.grid-cols>*>tr>.tableblock{border-width:0 1px 0 0}
|
||
|
|
table.grid-rows>thead>tr>.tableblock,table.grid-rows>tbody>tr>.tableblock{border-width:0 0 1px}
|
||
|
|
table.grid-rows>tfoot>tr>.tableblock{border-width:1px 0 0}
|
||
|
|
table.grid-all>*>tr>.tableblock:last-child,table.grid-cols>*>tr>.tableblock:last-child{border-right-width:0}
|
||
|
|
table.grid-all>tbody>tr:last-child>.tableblock,table.grid-all>thead:last-child>tr>.tableblock,table.grid-rows>tbody>tr:last-child>.tableblock,table.grid-rows>thead:last-child>tr>.tableblock{border-bottom-width:0}
|
||
|
|
table.frame-all{border-width:1px}
|
||
|
|
table.frame-sides{border-width:0 1px}
|
||
|
|
table.frame-topbot,table.frame-ends{border-width:1px 0}
|
||
|
|
table.stripes-all tr,table.stripes-odd tr:nth-of-type(odd){background:#f8f8f7}
|
||
|
|
table.stripes-none tr,table.stripes-odd tr:nth-of-type(even){background:none}
|
||
|
|
th.halign-left,td.halign-left{text-align:left}
|
||
|
|
th.halign-right,td.halign-right{text-align:right}
|
||
|
|
th.halign-center,td.halign-center{text-align:center}
|
||
|
|
th.valign-top,td.valign-top{vertical-align:top}
|
||
|
|
th.valign-bottom,td.valign-bottom{vertical-align:bottom}
|
||
|
|
th.valign-middle,td.valign-middle{vertical-align:middle}
|
||
|
|
table thead th,table tfoot th{font-weight:bold}
|
||
|
|
tbody tr th{display:table-cell;line-height:1.6;background:#f7f8f7}
|
||
|
|
tbody tr th,tbody tr th p,tfoot tr th,tfoot tr th p{color:rgba(0,0,0,.8);font-weight:bold}
|
||
|
|
p.tableblock>code:only-child{background:none;padding:0}
|
||
|
|
p.tableblock{font-size:1em}
|
||
|
|
td>div.verse{white-space:pre}
|
||
|
|
ol{margin-left:1.75em}
|
||
|
|
ul li ol{margin-left:1.5em}
|
||
|
|
dl dd{margin-left:1.125em}
|
||
|
|
dl dd:last-child,dl dd:last-child>:last-child{margin-bottom:0}
|
||
|
|
ol>li p,ul>li p,ul dd,ol dd,.olist .olist,.ulist .ulist,.ulist .olist,.olist .ulist{margin-bottom:.625em}
|
||
|
|
ul.checklist,ul.none,ol.none,ul.no-bullet,ol.no-bullet,ol.unnumbered,ul.unstyled,ol.unstyled{list-style-type:none}
|
||
|
|
ul.no-bullet,ol.no-bullet,ol.unnumbered{margin-left:.625em}
|
||
|
|
ul.unstyled,ol.unstyled{margin-left:0}
|
||
|
|
ul.checklist{margin-left:.625em}
|
||
|
|
ul.checklist li>p:first-child>.fa-square-o:first-child,ul.checklist li>p:first-child>.fa-check-square-o:first-child{width:1.25em;font-size:.8em;position:relative;bottom:.125em}
|
||
|
|
ul.checklist li>p:first-child>input[type="checkbox"]:first-child{margin-right:.25em}
|
||
|
|
ul.inline{display:-ms-flexbox;display:-webkit-box;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap;list-style:none;margin:0 0 .625em -1.25em}
|
||
|
|
ul.inline>li{margin-left:1.25em}
|
||
|
|
.unstyled dl dt{font-weight:400;font-style:normal}
|
||
|
|
ol.arabic{list-style-type:decimal}
|
||
|
|
ol.decimal{list-style-type:decimal-leading-zero}
|
||
|
|
ol.loweralpha{list-style-type:lower-alpha}
|
||
|
|
ol.upperalpha{list-style-type:upper-alpha}
|
||
|
|
ol.lowerroman{list-style-type:lower-roman}
|
||
|
|
ol.upperroman{list-style-type:upper-roman}
|
||
|
|
ol.lowergreek{list-style-type:lower-greek}
|
||
|
|
.hdlist>table,.colist>table{border:0;background:none}
|
||
|
|
.hdlist>table>tbody>tr,.colist>table>tbody>tr{background:none}
|
||
|
|
td.hdlist1,td.hdlist2{vertical-align:top;padding:0 .625em}
|
||
|
|
td.hdlist1{font-weight:bold;padding-bottom:1.25em}
|
||
|
|
.literalblock+.colist,.listingblock+.colist{margin-top:-.5em}
|
||
|
|
.colist td:not([class]):first-child{padding:.4em .75em 0;line-height:1;vertical-align:top}
|
||
|
|
.colist td:not([class]):first-child img{max-width:none}
|
||
|
|
.colist td:not([class]):last-child{padding:.25em 0}
|
||
|
|
.thumb,.th{line-height:0;display:inline-block;border:solid 4px #fff;-webkit-box-shadow:0 0 0 1px #ddd;box-shadow:0 0 0 1px #ddd}
|
||
|
|
.imageblock.left{margin:.25em .625em 1.25em 0}
|
||
|
|
.imageblock.right{margin:.25em 0 1.25em .625em}
|
||
|
|
.imageblock>.title{margin-bottom:0}
|
||
|
|
.imageblock.thumb,.imageblock.th{border-width:6px}
|
||
|
|
.imageblock.thumb>.title,.imageblock.th>.title{padding:0 .125em}
|
||
|
|
.image.left,.image.right{margin-top:.25em;margin-bottom:.25em;display:inline-block;line-height:0}
|
||
|
|
.image.left{margin-right:.625em}
|
||
|
|
.image.right{margin-left:.625em}
|
||
|
|
a.image{text-decoration:none;display:inline-block}
|
||
|
|
a.image object{pointer-events:none}
|
||
|
|
sup.footnote,sup.footnoteref{font-size:.875em;position:static;vertical-align:super}
|
||
|
|
sup.footnote a,sup.footnoteref a{text-decoration:none}
|
||
|
|
sup.footnote a:active,sup.footnoteref a:active{text-decoration:underline}
|
||
|
|
#footnotes{padding-top:.75em;padding-bottom:.75em;margin-bottom:.625em}
|
||
|
|
#footnotes hr{width:20%;min-width:6.25em;margin:-.25em 0 .75em;border-width:1px 0 0}
|
||
|
|
#footnotes .footnote{padding:0 .375em 0 .225em;line-height:1.3334;font-size:.875em;margin-left:1.2em;margin-bottom:.2em}
|
||
|
|
#footnotes .footnote a:first-of-type{font-weight:bold;text-decoration:none;margin-left:-1.05em}
|
||
|
|
#footnotes .footnote:last-of-type{margin-bottom:0}
|
||
|
|
#content #footnotes{margin-top:-.625em;margin-bottom:0;padding:.75em 0}
|
||
|
|
.gist .file-data>table{border:0;background:#fff;width:100%;margin-bottom:0}
|
||
|
|
.gist .file-data>table td.line-data{width:99%}
|
||
|
|
div.unbreakable{page-break-inside:avoid}
|
||
|
|
.big{font-size:larger}
|
||
|
|
.small{font-size:smaller}
|
||
|
|
.underline{text-decoration:underline}
|
||
|
|
.overline{text-decoration:overline}
|
||
|
|
.line-through{text-decoration:line-through}
|
||
|
|
.aqua{color:#00bfbf}
|
||
|
|
.aqua-background{background-color:#00fafa}
|
||
|
|
.black{color:#000}
|
||
|
|
.black-background{background-color:#000}
|
||
|
|
.blue{color:#0000bf}
|
||
|
|
.blue-background{background-color:#0000fa}
|
||
|
|
.fuchsia{color:#bf00bf}
|
||
|
|
.fuchsia-background{background-color:#fa00fa}
|
||
|
|
.gray{color:#606060}
|
||
|
|
.gray-background{background-color:#7d7d7d}
|
||
|
|
.green{color:#006000}
|
||
|
|
.green-background{background-color:#007d00}
|
||
|
|
.lime{color:#00bf00}
|
||
|
|
.lime-background{background-color:#00fa00}
|
||
|
|
.maroon{color:#600000}
|
||
|
|
.maroon-background{background-color:#7d0000}
|
||
|
|
.navy{color:#000060}
|
||
|
|
.navy-background{background-color:#00007d}
|
||
|
|
.olive{color:#606000}
|
||
|
|
.olive-background{background-color:#7d7d00}
|
||
|
|
.purple{color:#600060}
|
||
|
|
.purple-background{background-color:#7d007d}
|
||
|
|
.red{color:#bf0000}
|
||
|
|
.red-background{background-color:#fa0000}
|
||
|
|
.silver{color:#909090}
|
||
|
|
.silver-background{background-color:#bcbcbc}
|
||
|
|
.teal{color:#006060}
|
||
|
|
.teal-background{background-color:#007d7d}
|
||
|
|
.white{color:#bfbfbf}
|
||
|
|
.white-background{background-color:#fafafa}
|
||
|
|
.yellow{color:#bfbf00}
|
||
|
|
.yellow-background{background-color:#fafa00}
|
||
|
|
span.icon>.fa{cursor:default}
|
||
|
|
a span.icon>.fa{cursor:inherit}
|
||
|
|
.admonitionblock td.icon [class^="fa icon-"]{font-size:2.5em;text-shadow:1px 1px 2px rgba(0,0,0,.5);cursor:default}
|
||
|
|
.admonitionblock td.icon .icon-note::before{content:"\f05a";color:#19407c}
|
||
|
|
.admonitionblock td.icon .icon-tip::before{content:"\f0eb";text-shadow:1px 1px 2px rgba(155,155,0,.8);color:#111}
|
||
|
|
.admonitionblock td.icon .icon-warning::before{content:"\f071";color:#bf6900}
|
||
|
|
.admonitionblock td.icon .icon-caution::before{content:"\f06d";color:#bf3400}
|
||
|
|
.admonitionblock td.icon .icon-important::before{content:"\f06a";color:#bf0000}
|
||
|
|
.conum[data-value]{display:inline-block;color:#fff!important;background-color:rgba(0,0,0,.8);-webkit-border-radius:100px;border-radius:100px;text-align:center;font-size:.75em;width:1.67em;height:1.67em;line-height:1.67em;font-family:"Open Sans","DejaVu Sans",sans-serif;font-style:normal;font-weight:bold}
|
||
|
|
.conum[data-value] *{color:#fff!important}
|
||
|
|
.conum[data-value]+b{display:none}
|
||
|
|
.conum[data-value]::after{content:attr(data-value)}
|
||
|
|
pre .conum[data-value]{position:relative;top:-.125em}
|
||
|
|
b.conum *{color:inherit!important}
|
||
|
|
.conum:not([data-value]):empty{display:none}
|
||
|
|
dt,th.tableblock,td.content,div.footnote{text-rendering:optimizeLegibility}
|
||
|
|
h1,h2,p,td.content,span.alt{letter-spacing:-.01em}
|
||
|
|
p strong,td.content strong,div.footnote strong{letter-spacing:-.005em}
|
||
|
|
p,blockquote,dt,td.content,span.alt{font-size:1.0625rem}
|
||
|
|
p{margin-bottom:1.25rem}
|
||
|
|
.sidebarblock p,.sidebarblock dt,.sidebarblock td.content,p.tableblock{font-size:1em}
|
||
|
|
.exampleblock>.content{background-color:#fffef7;border-color:#e0e0dc;-webkit-box-shadow:0 1px 4px #e0e0dc;box-shadow:0 1px 4px #e0e0dc}
|
||
|
|
.print-only{display:none!important}
|
||
|
|
@page{margin:1.25cm .75cm}
|
||
|
|
@media print{*{-webkit-box-shadow:none!important;box-shadow:none!important;text-shadow:none!important}
|
||
|
|
html{font-size:80%}
|
||
|
|
a{color:inherit!important;text-decoration:underline!important}
|
||
|
|
a.bare,a[href^="#"],a[href^="mailto:"]{text-decoration:none!important}
|
||
|
|
a[href^="http:"]:not(.bare)::after,a[href^="https:"]:not(.bare)::after{content:"(" attr(href) ")";display:inline-block;font-size:.875em;padding-left:.25em}
|
||
|
|
abbr[title]::after{content:" (" attr(title) ")"}
|
||
|
|
pre,blockquote,tr,img,object,svg{page-break-inside:avoid}
|
||
|
|
thead{display:table-header-group}
|
||
|
|
svg{max-width:100%}
|
||
|
|
p,blockquote,dt,td.content{font-size:1em;orphans:3;widows:3}
|
||
|
|
h2,h3,#toctitle,.sidebarblock>.content>.title{page-break-after:avoid}
|
||
|
|
#toc,.sidebarblock,.exampleblock>.content{background:none!important}
|
||
|
|
#toc{border-bottom:1px solid #dddddf!important;padding-bottom:0!important}
|
||
|
|
body.book #header{text-align:center}
|
||
|
|
body.book #header>h1:first-child{border:0!important;margin:2.5em 0 1em}
|
||
|
|
body.book #header .details{border:0!important;display:block;padding:0!important}
|
||
|
|
body.book #header .details span:first-child{margin-left:0!important}
|
||
|
|
body.book #header .details br{display:block}
|
||
|
|
body.book #header .details br+span::before{content:none!important}
|
||
|
|
body.book #toc{border:0!important;text-align:left!important;padding:0!important;margin:0!important}
|
||
|
|
body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-break-before:always}
|
||
|
|
.listingblock code[data-lang]::before{display:block}
|
||
|
|
#footer{padding:0 .9375em}
|
||
|
|
.hide-on-print{display:none!important}
|
||
|
|
.print-only{display:block!important}
|
||
|
|
.hide-for-print{display:none!important}
|
||
|
|
.show-for-print{display:inherit!important}}
|
||
|
|
@media print,amzn-kf8{#header>h1:first-child{margin-top:1.25rem}
|
||
|
|
.sect1{padding:0!important}
|
||
|
|
.sect1+.sect1{border:0}
|
||
|
|
#footer{background:none}
|
||
|
|
#footer-text{color:rgba(0,0,0,.6);font-size:.9em}}
|
||
|
|
@media amzn-kf8{#header,#content,#footnotes,#footer{padding:0}}
|
||
|
|
</style>
|
||
|
|
</head>
|
||
|
|
<body class="article">
|
||
|
|
<div id="header">
|
||
|
|
<h1>Use of index and Racy Git problem</h1>
|
||
|
|
</div>
|
||
|
|
<div id="content">
|
||
|
|
<div class="sect1">
|
||
|
|
<h2 id="_background">Background</h2>
|
||
|
|
<div class="sectionbody">
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>The index is one of the most important data structures in Git.
|
||
|
|
It represents a virtual working tree state by recording list of
|
||
|
|
paths and their object names and serves as a staging area to
|
||
|
|
write out the next tree object to be committed. The state is
|
||
|
|
"virtual" in the sense that it does not necessarily have to, and
|
||
|
|
often does not, match the files in the working tree.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>There are cases Git needs to examine the differences between the
|
||
|
|
virtual working tree state in the index and the files in the
|
||
|
|
working tree. The most obvious case is when the user asks <code>git
|
||
|
|
diff</code> (or its low level implementation, <code>git diff-files</code>) or
|
||
|
|
<code>git-ls-files --modified</code>. In addition, Git internally checks
|
||
|
|
if the files in the working tree are different from what are
|
||
|
|
recorded in the index to avoid stomping on local changes in them
|
||
|
|
during patch application, switching branches, and merging.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>In order to speed up this comparison between the files in the
|
||
|
|
working tree and the index entries, the index entries record the
|
||
|
|
information obtained from the filesystem via <code>lstat(2)</code> system
|
||
|
|
call when they were last updated. When checking if they differ,
|
||
|
|
Git first runs <code>lstat(2)</code> on the files and compares the result
|
||
|
|
with this information (this is what was originally done by the
|
||
|
|
<code>ce_match_stat()</code> function, but the current code does it in
|
||
|
|
<code>ce_match_stat_basic()</code> function). If some of these "cached
|
||
|
|
stat information" fields do not match, Git can tell that the
|
||
|
|
files are modified without even looking at their contents.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Note: not all members in <code>struct stat</code> obtained via <code>lstat(2)</code>
|
||
|
|
are used for this comparison. For example, <code>st_atime</code> obviously
|
||
|
|
is not useful. Currently, Git compares the file type (regular
|
||
|
|
files vs symbolic links) and executable bits (only for regular
|
||
|
|
files) from <code>st_mode</code> member, <code>st_mtime</code> and <code>st_ctime</code>
|
||
|
|
timestamps, <code>st_uid</code>, <code>st_gid</code>, <code>st_ino</code>, and <code>st_size</code> members.
|
||
|
|
With a <code>USE_STDEV</code> compile-time option, <code>st_dev</code> is also
|
||
|
|
compared, but this is not enabled by default because this member
|
||
|
|
is not stable on network filesystems. With <code>USE_NSEC</code>
|
||
|
|
compile-time option, <code>st_mtim.tv_nsec</code> and <code>st_ctim.tv_nsec</code>
|
||
|
|
members are also compared. On Linux, this is not enabled by default
|
||
|
|
because in-core timestamps can have finer granularity than
|
||
|
|
on-disk timestamps, resulting in meaningless changes when an
|
||
|
|
inode is evicted from the inode cache. See commit 8ce13b0
|
||
|
|
of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
|
||
|
|
([PATCH] Sync in core time granularity with filesystems,
|
||
|
|
2005-01-04). This patch is included in kernel 2.6.11 and newer, but
|
||
|
|
only fixes the issue for file systems with exactly 1 ns or 1 s
|
||
|
|
resolution. Other file systems are still broken in current Linux
|
||
|
|
kernels (e.g. CEPH, CIFS, NTFS, UDF), see
|
||
|
|
<a href="https://lkml.org/lkml/2015/6/9/714" class="bare">https://lkml.org/lkml/2015/6/9/714</a></p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="sect1">
|
||
|
|
<h2 id="_racy_git">Racy Git</h2>
|
||
|
|
<div class="sectionbody">
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>There is one slight problem with the optimization based on the
|
||
|
|
cached stat information. Consider this sequence:</p>
|
||
|
|
</div>
|
||
|
|
<div class="literalblock">
|
||
|
|
<div class="content">
|
||
|
|
<pre>: modify 'foo'
|
||
|
|
$ git update-index 'foo'
|
||
|
|
: modify 'foo' again, in-place, without changing its size</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>The first <code>update-index</code> computes the object name of the
|
||
|
|
contents of file <code>foo</code> and updates the index entry for <code>foo</code>
|
||
|
|
along with the <code>struct stat</code> information. If the modification
|
||
|
|
that follows it happens very fast so that the file’s <code>st_mtime</code>
|
||
|
|
timestamp does not change, after this sequence, the cached stat
|
||
|
|
information the index entry records still exactly match what you
|
||
|
|
would see in the filesystem, even though the file <code>foo</code> is now
|
||
|
|
different.
|
||
|
|
This way, Git can incorrectly think files in the working tree
|
||
|
|
are unmodified even though they actually are. This is called
|
||
|
|
the "racy Git" problem (discovered by Pasky), and the entries
|
||
|
|
that appear clean when they may not be because of this problem
|
||
|
|
are called "racily clean".</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>To avoid this problem, Git does two things:</p>
|
||
|
|
</div>
|
||
|
|
<div class="olist arabic">
|
||
|
|
<ol class="arabic">
|
||
|
|
<li>
|
||
|
|
<p>When the cached stat information says the file has not been
|
||
|
|
modified, and the <code>st_mtime</code> is the same as (or newer than)
|
||
|
|
the timestamp of the index file itself (which is the time <code>git
|
||
|
|
update-index foo</code> finished running in the above example), it
|
||
|
|
also compares the contents with the object registered in the
|
||
|
|
index entry to make sure they match.</p>
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
<p>When the index file is updated that contains racily clean
|
||
|
|
entries, cached <code>st_size</code> information is truncated to zero
|
||
|
|
before writing a new version of the index file.</p>
|
||
|
|
</li>
|
||
|
|
</ol>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Because the index file itself is written after collecting all
|
||
|
|
the stat information from updated paths, <code>st_mtime</code> timestamp of
|
||
|
|
it is usually the same as or newer than any of the paths the
|
||
|
|
index contains. And no matter how quick the modification that
|
||
|
|
follows <code>git update-index foo</code> finishes, the resulting
|
||
|
|
<code>st_mtime</code> timestamp on <code>foo</code> cannot get a value earlier
|
||
|
|
than the index file. Therefore, index entries that can be
|
||
|
|
racily clean are limited to the ones that have the same
|
||
|
|
timestamp as the index file itself.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>The callers that want to check if an index entry matches the
|
||
|
|
corresponding file in the working tree continue to call
|
||
|
|
<code>ce_match_stat()</code>, but with this change, <code>ce_match_stat()</code> uses
|
||
|
|
<code>ce_modified_check_fs()</code> to see if racily clean ones are
|
||
|
|
actually clean after comparing the cached stat information using
|
||
|
|
<code>ce_match_stat_basic()</code>.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>The problem the latter solves is this sequence:</p>
|
||
|
|
</div>
|
||
|
|
<div class="literalblock">
|
||
|
|
<div class="content">
|
||
|
|
<pre>$ git update-index 'foo'
|
||
|
|
: modify 'foo' in-place without changing its size
|
||
|
|
: wait for enough time
|
||
|
|
$ git update-index 'bar'</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Without the latter, the timestamp of the index file gets a newer
|
||
|
|
value, and falsely clean entry <code>foo</code> would not be caught by the
|
||
|
|
timestamp comparison check done with the former logic anymore.
|
||
|
|
The latter makes sure that the cached stat information for <code>foo</code>
|
||
|
|
would never match with the file in the working tree, so later
|
||
|
|
checks by <code>ce_match_stat_basic()</code> would report that the index entry
|
||
|
|
does not match the file and Git does not have to fall back on more
|
||
|
|
expensive <code>ce_modified_check_fs()</code>.</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="sect1">
|
||
|
|
<h2 id="_runtime_penalty">Runtime penalty</h2>
|
||
|
|
<div class="sectionbody">
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>The runtime penalty of falling back to <code>ce_modified_check_fs()</code>
|
||
|
|
from <code>ce_match_stat()</code> can be very expensive when there are many
|
||
|
|
racily clean entries. An obvious way to artificially create
|
||
|
|
this situation is to give the same timestamp to all the files in
|
||
|
|
the working tree in a large project, run <code>git update-index</code> on
|
||
|
|
them, and give the same timestamp to the index file:</p>
|
||
|
|
</div>
|
||
|
|
<div class="literalblock">
|
||
|
|
<div class="content">
|
||
|
|
<pre>$ date >.datestamp
|
||
|
|
$ git ls-files | xargs touch -r .datestamp
|
||
|
|
$ git ls-files | git update-index --stdin
|
||
|
|
$ touch -r .datestamp .git/index</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>This will make all index entries racily clean. The linux project, for
|
||
|
|
example, there are over 20,000 files in the working tree. On my
|
||
|
|
Athlon 64 X2 3800+, after the above:</p>
|
||
|
|
</div>
|
||
|
|
<div class="literalblock">
|
||
|
|
<div class="content">
|
||
|
|
<pre>$ /usr/bin/time git diff-files
|
||
|
|
1.68user 0.54system 0:02.22elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
|
||
|
|
0inputs+0outputs (0major+67111minor)pagefaults 0swaps
|
||
|
|
$ git update-index MAINTAINERS
|
||
|
|
$ /usr/bin/time git diff-files
|
||
|
|
0.02user 0.12system 0:00.14elapsed 100%CPU (0avgtext+0avgdata 0maxresident)k
|
||
|
|
0inputs+0outputs (0major+935minor)pagefaults 0swaps</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Running <code>git update-index</code> in the middle checked the racily
|
||
|
|
clean entries, and left the cached <code>st_mtime</code> for all the paths
|
||
|
|
intact because they were actually clean (so this step took about
|
||
|
|
the same amount of time as the first <code>git diff-files</code>). After
|
||
|
|
that, they are not racily clean anymore but are truly clean, so
|
||
|
|
the second invocation of <code>git diff-files</code> fully took advantage
|
||
|
|
of the cached stat information.</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div class="sect1">
|
||
|
|
<h2 id="_avoiding_runtime_penalty">Avoiding runtime penalty</h2>
|
||
|
|
<div class="sectionbody">
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>In order to avoid the above runtime penalty, post 1.4.2 Git used
|
||
|
|
to have a code that made sure the index file
|
||
|
|
got timestamp newer than the youngest files in the index when
|
||
|
|
there are many young files with the same timestamp as the
|
||
|
|
resulting index file would otherwise would have by waiting
|
||
|
|
before finishing writing the index file out.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>I suspected that in practice the situation where many paths in the
|
||
|
|
index are all racily clean was quite rare. The only code paths
|
||
|
|
that can record recent timestamp for large number of paths are:</p>
|
||
|
|
</div>
|
||
|
|
<div class="olist arabic">
|
||
|
|
<ol class="arabic">
|
||
|
|
<li>
|
||
|
|
<p>Initial <code>git add .</code> of a large project.</p>
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
<p><code>git checkout</code> of a large project from an empty index into an
|
||
|
|
unpopulated working tree.</p>
|
||
|
|
</li>
|
||
|
|
</ol>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Note: switching branches with <code>git checkout</code> keeps the cached
|
||
|
|
stat information of existing working tree files that are the
|
||
|
|
same between the current branch and the new branch, which are
|
||
|
|
all older than the resulting index file, and they will not
|
||
|
|
become racily clean. Only the files that are actually checked
|
||
|
|
out can become racily clean.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>In a large project where raciness avoidance cost really matters,
|
||
|
|
however, the initial computation of all object names in the
|
||
|
|
index takes more than one second, and the index file is written
|
||
|
|
out after all that happens. Therefore the timestamp of the
|
||
|
|
index file will be more than one seconds later than the
|
||
|
|
youngest file in the working tree. This means that in these
|
||
|
|
cases there actually will not be any racily clean entry in
|
||
|
|
the resulting index.</p>
|
||
|
|
</div>
|
||
|
|
<div class="paragraph">
|
||
|
|
<p>Based on this discussion, the current code does not use the
|
||
|
|
"workaround" to avoid the runtime penalty that does not exist in
|
||
|
|
practice anymore. This was done with commit 0fc82cff on Aug 15,
|
||
|
|
2006.</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div id="footer">
|
||
|
|
<div id="footer-text">
|
||
|
|
Last updated 2019-02-26 19:31:11 UTC
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|