<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="generator" content="AsciiDoc 8.5.2" />
<title>lockfile API</title>
<style type="text/css">
/* Debug borders */
p, li, dt, dd, div, pre, h1, h2, h3, h4, h5, h6 {
/*
border: 1px solid red;
*/
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
tt {
color: navy;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
font-family: sans-serif;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
div.sectionbody {
font-family: serif;
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
pre {
padding: 0;
margin: 0;
}
span#author {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
font-size: 1.1em;
}
span#email {
}
span#revnumber, span#revdate, span#revremark {
font-family: sans-serif;
}
div#footer {
font-family: sans-serif;
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
div#footer-text {
float: left;
padding-bottom: 0.5em;
}
div#footer-badges {
float: right;
padding-bottom: 0.5em;
}
div#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.tableblock, div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
}
/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
}
div.title + * {
margin-top: 0;
}
td div.title:first-child {
margin-top: 0.0em;
}
div.content div.title:first-child {
margin-top: 0.0em;
}
div.content + div.title {
margin-top: 0.0em;
}
div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.listingblock > div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #dddddd;
color: #777777;
}
div.quoteblock > div.attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock > div.content {
white-space: pre;
}
div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
}
div.admonitionblock td.content {
padding-left: 0.5em;
border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; }
a.image:visited { color: white; }
dl {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
dt {
margin-top: 0.5em;
margin-bottom: 0;
font-style: normal;
color: navy;
}
dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
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;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-family: sans-serif;
font-weight: bold;
}
tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overriden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
}
td.hdlist1 {
vertical-align: top;
font-style: normal;
padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
@media print {
div#footer-badges { display: none; }
}
div#toc {
margin-bottom: 2.5em;
}
div#toctitle {
color: #527bbd;
font-family: sans-serif;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
/* Workarounds for IE6's broken and incomplete CSS2. */
div.sidebar-content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.sidebar-title, div.image-title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
margin-top: 0.0em;
margin-bottom: 0.5em;
}
div.listingblock div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock-attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock-content {
white-space: pre;
}
div.verseblock-attribution {
padding-top: 0.75em;
text-align: left;
}
div.exampleblock-content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
/* IE6 sets dynamically generated links as visited. */
div#toc a:visited { color: blue; }
</style>
<script type="text/javascript">
window.onload = function(){asciidoc.footnotes();}
var asciidoc = {
toc: function (toclevels) {
function getText(el) {
var text = "";
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 3 ) text += i.data;
else if (i.firstChild != null)
text += getText(i);
}
return text;
}
function TocEntry(el, text, toclevel) {
this.element = el;
this.text = text;
this.toclevel = toclevel;
}
function tocEntries(el, toclevels) {
var result = new Array;
var re = new RegExp('[hH]([2-'+(toclevels+1)+'])');
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 ) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
footnotes: function () {
var cont = document.getElementById("content");
var noteholder = document.getElementById("footnotes");
var spans = cont.getElementsByTagName("span");
var refs = {};
var n = 0;
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnote") {
n++;
note = spans[i].innerHTML.match(/\s*\[([\s\S]*)]\s*/)[1];
noteholder.innerHTML +=
"<div class='footnote' id='_footnote_" + n + "'>" +
"<a href='#_footnoteref_" + n + "' title='Return to text'>" +
n + "</a>. " + note + "</div>";
spans[i].innerHTML =
"[<a id='_footnoteref_" + n + "' href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
var id =spans[i].getAttribute("id");
if (id != null) refs["#"+id] = n;
}
}
if (n == 0)
noteholder.parentNode.removeChild(noteholder);
else {
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnoteref") {
var href = spans[i].getElementsByTagName("a")[0].getAttribute("href");
href = href.match(/#.*/)[0]; n = refs[href];
spans[i].innerHTML =
"[<a href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
}
}
}
}
}
</script>
</head>
<body>
<div id="header">
<h1>lockfile API</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>The lockfile API serves two purposes:</p></div>
<div class="ulist"><ul>
<li>
<p>
Mutual exclusion. When we write out a new index file, first
we create a new file <tt>$GIT_DIR/index.lock</tt>, write the new
contents into it, and rename it to the final destination
<tt>$GIT_DIR/index</tt>. We try to create the <tt>$GIT_DIR/index.lock</tt>
file with O_EXCL so that we can notice and fail when somebody
else is already trying to update the index file.
</p>
</li>
<li>
<p>
Automatic cruft removal. After we create the "lock" file, we
may decide to <tt>die()</tt>, and we would want to make sure that we
remove the file that has not been committed to its final
destination. This is done by remembering the lockfiles we
created in a linked list and cleaning them up from an
<tt>atexit(3)</tt> handler. Outstanding lockfiles are also removed
when the program dies on a signal.
</p>
</li>
</ul></div>
</div>
</div>
<h2 id="_the_functions">The functions</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
hold_lock_file_for_update
</dt>
<dd>
<p>
Take a pointer to <tt>struct lock_file</tt>, the filename of
the final destination (e.g. <tt>$GIT_DIR/index</tt>) and a flag
<tt>die_on_error</tt>. Attempt to create a lockfile for the
destination and return the file descriptor for writing
to the file. If <tt>die_on_error</tt> flag is true, it dies if
a lock is already taken for the file; otherwise it
returns a negative integer to the caller on failure.
</p>
</dd>
<dt class="hdlist1">
commit_lock_file
</dt>
<dd>
<p>
Take a pointer to the <tt>struct lock_file</tt> initialized
with an earlier call to <tt>hold_lock_file_for_update()</tt>,
close the file descriptor and rename the lockfile to its
final destination. Returns 0 upon success, a negative
value on failure to close(2) or rename(2).
</p>
</dd>
<dt class="hdlist1">
rollback_lock_file
</dt>
<dd>
<p>
Take a pointer to the <tt>struct lock_file</tt> initialized
with an earlier call to <tt>hold_lock_file_for_update()</tt>,
close the file descriptor and remove the lockfile.
</p>
</dd>
<dt class="hdlist1">
close_lock_file
</dt>
<dd>
<p>
Take a pointer to the <tt>struct lock_file</tt> initialized
with an earlier call to <tt>hold_lock_file_for_update()</tt>,
and close the file descriptor. Returns 0 upon success,
a negative value on failure to close(2).
</p>
</dd>
</dl></div>
<div class="paragraph"><p>Because the structure is used in an <tt>atexit(3)</tt> handler, its
storage has to stay throughout the life of the program. It
cannot be an auto variable allocated on the stack.</p></div>
<div class="paragraph"><p>Call <tt>commit_lock_file()</tt> or <tt>rollback_lock_file()</tt> when you are
done writing to the file descriptor. If you do not call either
and simply <tt>exit(3)</tt> from the program, an <tt>atexit(3)</tt> handler
will close and remove the lockfile.</p></div>
<div class="paragraph"><p>If you need to close the file descriptor you obtained from
<tt>hold_lock_file_for_update</tt> function yourself, do so by calling
<tt>close_lock_file()</tt>. You should never call <tt>close(2)</tt> yourself!
Otherwise the <tt>struct
lock_file</tt> structure still remembers that the file descriptor
needs to be closed, and a later call to <tt>commit_lock_file()</tt> or
<tt>rollback_lock_file()</tt> will result in duplicate calls to
<tt>close(2)</tt>. Worse yet, if you <tt>close(2)</tt>, open another file
descriptor for completely different purpose, and then call
<tt>commit_lock_file()</tt> or <tt>rollback_lock_file()</tt>, they may close
that unrelated file descriptor.</p></div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated 2011-11-15 13:45:02 PDT
</div>
</div>
</body>
</html>