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<body><div class="doctools">
<h1 class="doctools_title">tsv(n) 2.8 "Tcl Threading"</h1>
<div id="name" class="doctools_section"><h2><a name="name">Name</a></h2>
<p>tsv - Part of the Tcl threading extension allowing script level manipulation of data shared between threads.</p>
</div>
<div id="toc" class="doctools_section"><h2><a name="toc">Table Of Contents</a></h2>
<ul class="doctools_toc">
<li class="doctools_section"><a href="#toc">Table Of Contents</a></li>
<li class="doctools_section"><a href="#synopsis">Synopsis</a></li>
<li class="doctools_section"><a href="#section1">Description</a></li>
<li class="doctools_section"><a href="#section2">ELEMENT COMMANDS</a></li>
<li class="doctools_section"><a href="#section3">LIST COMMANDS</a></li>
<li class="doctools_section"><a href="#section4">ARRAY COMMANDS</a></li>
<li class="doctools_section"><a href="#section5">KEYED LIST COMMANDS</a></li>
<li class="doctools_section"><a href="#section6">DISCUSSION</a></li>
<li class="doctools_section"><a href="#section7">CREDITS</a></li>
<li class="doctools_section"><a href="#see-also">See Also</a></li>
<li class="doctools_section"><a href="#keywords">Keywords</a></li>
</ul>
</div>
<div id="synopsis" class="doctools_section"><h2><a name="synopsis">Synopsis</a></h2>
<div class="doctools_synopsis">
<ul class="doctools_requirements">
<li>package require <b class="pkgname">Tcl 8.7</b></li>
<li>package require <b class="pkgname">thread <span class="opt">?2.9?</span></b></li>
</ul>
<ul class="doctools_syntax">
<li><a href="#1"><b class="cmd">tsv::names</b> <span class="opt">?pattern?</span></a></li>
<li><a href="#2"><b class="cmd">tsv::object</b> <i class="arg">varname</i> <i class="arg">element</i></a></li>
<li><a href="#3"><b class="cmd">tsv::set</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?value?</span></a></li>
<li><a href="#4"><b class="cmd">tsv::get</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?namedvar?</span></a></li>
<li><a href="#5"><b class="cmd">tsv::unset</b> <i class="arg">varname</i> <span class="opt">?element?</span></a></li>
<li><a href="#6"><b class="cmd">tsv::exists</b> <i class="arg">varname</i> <i class="arg">element</i></a></li>
<li><a href="#7"><b class="cmd">tsv::pop</b> <i class="arg">varname</i> <i class="arg">element</i></a></li>
<li><a href="#8"><b class="cmd">tsv::move</b> <i class="arg">varname</i> <i class="arg">oldname</i> <i class="arg">newname</i></a></li>
<li><a href="#9"><b class="cmd">tsv::incr</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?count?</span></a></li>
<li><a href="#10"><b class="cmd">tsv::append</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></li>
<li><a href="#11"><b class="cmd">tsv::lock</b> <i class="arg">varname</i> <i class="arg">arg</i> <span class="opt">?arg ...?</span></a></li>
<li><a href="#12"><b class="cmd">tsv::handlers</b></a></li>
<li><a href="#13"><b class="cmd">tsv::lappend</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></li>
<li><a href="#14"><b class="cmd">tsv::linsert</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">index</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></li>
<li><a href="#15"><b class="cmd">tsv::lreplace</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">first</i> <i class="arg">last</i> <span class="opt">?value ...?</span></a></li>
<li><a href="#16"><b class="cmd">tsv::llength</b> <i class="arg">varname</i> <i class="arg">element</i></a></li>
<li><a href="#17"><b class="cmd">tsv::lindex</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></li>
<li><a href="#18"><b class="cmd">tsv::lrange</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">from</i> <i class="arg">to</i></a></li>
<li><a href="#19"><b class="cmd">tsv::lsearch</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?options?</span> <i class="arg">pattern</i></a></li>
<li><a href="#20"><b class="cmd">tsv::lset</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">index</i> <span class="opt">?index ...?</span> <i class="arg">value</i></a></li>
<li><a href="#21"><b class="cmd">tsv::lpop</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></li>
<li><a href="#22"><b class="cmd">tsv::lpush</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></li>
<li><a href="#23"><b class="cmd">tsv::array set</b> <i class="arg">varname</i> <i class="arg">list</i></a></li>
<li><a href="#24"><b class="cmd">tsv::array get</b> <i class="arg">varname</i> <span class="opt">?pattern?</span></a></li>
<li><a href="#25"><b class="cmd">tsv::array names</b> <i class="arg">varname</i> <span class="opt">?pattern?</span></a></li>
<li><a href="#26"><b class="cmd">tsv::array size</b> <i class="arg">varname</i></a></li>
<li><a href="#27"><b class="cmd">tsv::array reset</b> <i class="arg">varname</i> <i class="arg">list</i></a></li>
<li><a href="#28"><b class="cmd">tsv::array bind</b> <i class="arg">varname</i> <i class="arg">handle</i></a></li>
<li><a href="#29"><b class="cmd">tsv::array unbind</b> <i class="arg">varname</i></a></li>
<li><a href="#30"><b class="cmd">tsv::array isbound</b> <i class="arg">varname</i></a></li>
<li><a href="#31"><b class="cmd">tsv::keyldel</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i></a></li>
<li><a href="#32"><b class="cmd">tsv::keylget</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i> <span class="opt">?retvar?</span></a></li>
<li><a href="#33"><b class="cmd">tsv::keylkeys</b> <i class="arg">varname</i> <i class="arg">keylist</i> <span class="opt">?key?</span></a></li>
<li><a href="#34"><b class="cmd">tsv::keylset</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i> <i class="arg">value</i> <span class="opt">?key value..?</span></a></li>
</ul>
</div>
</div>
<div id="section1" class="doctools_section"><h2><a name="section1">Description</a></h2>
<p>This section describes commands implementing thread shared variables.
A thread shared variable is very similar to a Tcl array but in
contrast to a Tcl array it is created in shared memory and can
be accessed from many threads at the same time. Important feature of
thread shared variable is that each access to the variable is internally
protected by a mutex so script programmer does not have to take care
about locking the variable himself.</p>
<p>Thread shared variables are not bound to any thread explicitly. That
means that when a thread which created any of thread shared variables
exits, the variable and associated memory is not unset/reclaimed.
User has to explicitly unset the variable to reclaim the memory
consumed by the variable.</p>
</div>
<div id="section2" class="doctools_section"><h2><a name="section2">ELEMENT COMMANDS</a></h2>
<dl class="doctools_definitions">
<dt><a name="1"><b class="cmd">tsv::names</b> <span class="opt">?pattern?</span></a></dt>
<dd><p>Returns names of shared variables matching optional <span class="opt">?pattern?</span>
or all known variables if pattern is omitted.</p></dd>
<dt><a name="2"><b class="cmd">tsv::object</b> <i class="arg">varname</i> <i class="arg">element</i></a></dt>
<dd><p>Creates object accessor command for the <i class="arg">element</i> in the
shared variable <i class="arg">varname</i>. Using this command, one can apply most
of the other shared variable commands as method functions of
the element object command. The object command is automatically
deleted when the element which this command is pointing to is unset.</p>
<pre class="doctools_example">
% tsv::set foo bar "A shared string"
% set string [tsv::object foo bar]
% $string append " appended"
=> A shared string appended
</pre>
</dd>
<dt><a name="3"><b class="cmd">tsv::set</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?value?</span></a></dt>
<dd><p>Sets the value of the <i class="arg">element</i> in the shared variable <i class="arg">varname</i>
to <i class="arg">value</i> and returns the value to caller. The <i class="arg">value</i>
may be omitted, in which case the command will return the current
value of the element. If the element cannot be found, error is triggered.</p></dd>
<dt><a name="4"><b class="cmd">tsv::get</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?namedvar?</span></a></dt>
<dd><p>Retrieves the value of the <i class="arg">element</i> from the shared variable <i class="arg">varname</i>.
If the optional argument <i class="arg">namedvar</i> is given, the value is
stored in the named variable. Return value of the command depends
of the existence of the optional argument <i class="arg">namedvar</i>.
If the argument is omitted and the requested element cannot be found
in the shared array, the command triggers error. If, however, the
optional argument is given on the command line, the command returns
true (1) if the element is found or false (0) if the element is not found.</p></dd>
<dt><a name="5"><b class="cmd">tsv::unset</b> <i class="arg">varname</i> <span class="opt">?element?</span></a></dt>
<dd><p>Unsets the <i class="arg">element</i> from the shared variable <i class="arg">varname</i>.
If the optional element is not given, it deletes the variable.</p></dd>
<dt><a name="6"><b class="cmd">tsv::exists</b> <i class="arg">varname</i> <i class="arg">element</i></a></dt>
<dd><p>Checks whether the <i class="arg">element</i> exists in the shared variable <i class="arg">varname</i>
and returns true (1) if it does or false (0) if it doesn't.</p></dd>
<dt><a name="7"><b class="cmd">tsv::pop</b> <i class="arg">varname</i> <i class="arg">element</i></a></dt>
<dd><p>Returns value of the <i class="arg">element</i> in the shared variable <i class="arg">varname</i>
and unsets the element, all in one atomic operation.</p></dd>
<dt><a name="8"><b class="cmd">tsv::move</b> <i class="arg">varname</i> <i class="arg">oldname</i> <i class="arg">newname</i></a></dt>
<dd><p>Renames the element <i class="arg">oldname</i> to the <i class="arg">newname</i> in the
shared variable <i class="arg">varname</i>. This effectively performs an get/unset/set
sequence of operations but all in one atomic step.</p></dd>
<dt><a name="9"><b class="cmd">tsv::incr</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?count?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">incr</b> command but increments the value
of the <i class="arg">element</i> in shared variable <i class="arg">varname</i> instead of
the Tcl variable.</p></dd>
<dt><a name="10"><b class="cmd">tsv::append</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">append</b> command but appends one or more
values to the <i class="arg">element</i> in shared variable <i class="arg">varname</i> instead of the
Tcl variable.</p></dd>
<dt><a name="11"><b class="cmd">tsv::lock</b> <i class="arg">varname</i> <i class="arg">arg</i> <span class="opt">?arg ...?</span></a></dt>
<dd><p>This command concatenates passed arguments and evaluates the
resulting script under the internal mutex protection. During the
script evaluation, the entire shared variable is locked. For shared
variable commands within the script, internal locking is disabled
so no deadlock can occur. It is also allowed to unset the shared
variable from within the script. The shared variable is automatically
created if it did not exists at the time of the first lock operation.</p>
<pre class="doctools_example">
% tsv::lock foo {
tsv::lappend foo bar 1
tsv::lappend foo bar 2
puts stderr [tsv::set foo bar]
tsv::unset foo
}
</pre>
</dd>
<dt><a name="12"><b class="cmd">tsv::handlers</b></a></dt>
<dd><p>Returns the names of all persistent storage handlers enabled at compile time.
See <span class="sectref"><a href="#section4">ARRAY COMMANDS</a></span> for details.</p></dd>
</dl>
</div>
<div id="section3" class="doctools_section"><h2><a name="section3">LIST COMMANDS</a></h2>
<p>Those command are similar to the equivalently named Tcl command. The difference
is that they operate on elements of shared arrays.</p>
<dl class="doctools_definitions">
<dt><a name="13"><b class="cmd">tsv::lappend</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lappend</b> command but appends one
or more values to the <i class="arg">element</i> in shared variable <i class="arg">varname</i>
instead of the Tcl variable.</p></dd>
<dt><a name="14"><b class="cmd">tsv::linsert</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">index</i> <i class="arg">value</i> <span class="opt">?value ...?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">linsert</b> command but inserts one
or more values at the <i class="arg">index</i> list position in the
<i class="arg">element</i> in the shared variable <i class="arg">varname</i> instead of the Tcl variable.</p></dd>
<dt><a name="15"><b class="cmd">tsv::lreplace</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">first</i> <i class="arg">last</i> <span class="opt">?value ...?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lreplace</b> command but replaces one
or more values between the <i class="arg">first</i> and <i class="arg">last</i> position
in the <i class="arg">element</i> of the shared variable <i class="arg">varname</i> instead of
the Tcl variable.</p></dd>
<dt><a name="16"><b class="cmd">tsv::llength</b> <i class="arg">varname</i> <i class="arg">element</i></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">llength</b> command but returns length
of the <i class="arg">element</i> in the shared variable <i class="arg">varname</i> instead of the Tcl
variable.</p></dd>
<dt><a name="17"><b class="cmd">tsv::lindex</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lindex</b> command but returns the value
at the <i class="arg">index</i> list position of the <i class="arg">element</i> from
the shared variable <i class="arg">varname</i> instead of the Tcl variable.</p></dd>
<dt><a name="18"><b class="cmd">tsv::lrange</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">from</i> <i class="arg">to</i></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lrange</b> command but returns values
between <i class="arg">from</i> and <i class="arg">to</i> list positions from the
<i class="arg">element</i> in the shared variable <i class="arg">varname</i> instead of the Tcl variable.</p></dd>
<dt><a name="19"><b class="cmd">tsv::lsearch</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?options?</span> <i class="arg">pattern</i></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lsearch</b> command but searches the <i class="arg">element</i>
in the shared variable <i class="arg">varname</i> instead of the Tcl variable.</p></dd>
<dt><a name="20"><b class="cmd">tsv::lset</b> <i class="arg">varname</i> <i class="arg">element</i> <i class="arg">index</i> <span class="opt">?index ...?</span> <i class="arg">value</i></a></dt>
<dd><p>Similar to standard Tcl <b class="cmd">lset</b> command but sets the <i class="arg">element</i>
in the shared variable <i class="arg">varname</i> instead of the Tcl variable.</p></dd>
<dt><a name="21"><b class="cmd">tsv::lpop</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></dt>
<dd><p>Similar to the standard Tcl <b class="cmd">lindex</b> command but in addition to
returning, it also splices the value out of the <i class="arg">element</i>
from the shared variable <i class="arg">varname</i> in one atomic operation.
In contrast to the Tcl <b class="cmd">lindex</b> command, this command returns
no value to the caller.</p></dd>
<dt><a name="22"><b class="cmd">tsv::lpush</b> <i class="arg">varname</i> <i class="arg">element</i> <span class="opt">?index?</span></a></dt>
<dd><p>This command performs the opposite of the <b class="cmd">tsv::lpop</b> command.
As its counterpart, it returns no value to the caller.</p></dd>
</dl>
</div>
<div id="section4" class="doctools_section"><h2><a name="section4">ARRAY COMMANDS</a></h2>
<p>This command supports most of the options of the standard Tcl
<b class="cmd">array</b> command. In addition to those, it allows binding
a shared variable to some persistent storage databases. Currently the persistent
options supported are the famous GNU Gdbm and LMDB. These options have to be
selected during the package compilation time.
The implementation provides hooks for defining other persistency layers, if
needed.</p>
<dl class="doctools_definitions">
<dt><a name="23"><b class="cmd">tsv::array set</b> <i class="arg">varname</i> <i class="arg">list</i></a></dt>
<dd><p>Does the same as standard Tcl <b class="cmd">array set</b>.</p></dd>
<dt><a name="24"><b class="cmd">tsv::array get</b> <i class="arg">varname</i> <span class="opt">?pattern?</span></a></dt>
<dd><p>Does the same as standard Tcl <b class="cmd">array get</b>.</p></dd>
<dt><a name="25"><b class="cmd">tsv::array names</b> <i class="arg">varname</i> <span class="opt">?pattern?</span></a></dt>
<dd><p>Does the same as standard Tcl <b class="cmd">array names</b>.</p></dd>
<dt><a name="26"><b class="cmd">tsv::array size</b> <i class="arg">varname</i></a></dt>
<dd><p>Does the same as standard Tcl <b class="cmd">array size</b>.</p></dd>
<dt><a name="27"><b class="cmd">tsv::array reset</b> <i class="arg">varname</i> <i class="arg">list</i></a></dt>
<dd><p>Does the same as standard Tcl <b class="cmd">array set</b> but it clears
the <i class="arg">varname</i> and sets new values from the list atomically.</p></dd>
<dt><a name="28"><b class="cmd">tsv::array bind</b> <i class="arg">varname</i> <i class="arg">handle</i></a></dt>
<dd><p>Binds the <i class="arg">varname</i> to the persistent storage <i class="arg">handle</i>.
The format of the <i class="arg">handle</i> is <handler>:<address>, where <handler> is
"gdbm" for GNU Gdbm and "lmdb" for LMDB and <address> is the path to the
database file.</p></dd>
<dt><a name="29"><b class="cmd">tsv::array unbind</b> <i class="arg">varname</i></a></dt>
<dd><p>Unbinds the shared <i class="arg">array</i> from its bound persistent storage.</p></dd>
<dt><a name="30"><b class="cmd">tsv::array isbound</b> <i class="arg">varname</i></a></dt>
<dd><p>Returns true (1) if the shared <i class="arg">varname</i> is bound to some
persistent storage or zero (0) if not.</p></dd>
</dl>
</div>
<div id="section5" class="doctools_section"><h2><a name="section5">KEYED LIST COMMANDS</a></h2>
<p>Keyed list commands are borrowed from the TclX package. Keyed lists provide
a structured data type built upon standard Tcl lists. This is a functionality
similar to structs in the C programming language.</p>
<p>A keyed list is a list in which each element contains a key and value
pair. These element pairs are stored as lists themselves, where the key
is the first element of the list, and the value is the second. The
key-value pairs are referred to as fields. This is an example of a
keyed list:</p>
<pre class="doctools_example">
{{NAME {Frank Zappa}} {JOB {musician and composer}}}
</pre>
<p>Fields may contain subfields; `.' is the separator character. Subfields
are actually fields where the value is another keyed list. Thus the
following list has the top level fields ID and NAME, and subfields
NAME.FIRST and NAME.LAST:</p>
<pre class="doctools_example">
{ID 106} {NAME {{FIRST Frank} {LAST Zappa}}}
</pre>
<p>There is no limit to the recursive depth of subfields,
allowing one to build complex data structures. Keyed lists are constructed
and accessed via a number of commands. All keyed list management
commands take the name of the variable containing the keyed list as an
argument (i.e. passed by reference), rather than passing the list directly.</p>
<dl class="doctools_definitions">
<dt><a name="31"><b class="cmd">tsv::keyldel</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i></a></dt>
<dd><p>Delete the field specified by <i class="arg">key</i> from the keyed list <i class="arg">keylist</i>
in the shared variable <i class="arg">varname</i>.
This removes both the key and the value from the keyed list.</p></dd>
<dt><a name="32"><b class="cmd">tsv::keylget</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i> <span class="opt">?retvar?</span></a></dt>
<dd><p>Return the value associated with <i class="arg">key</i> from the keyed list <i class="arg">keylist</i>
in the shared variable <i class="arg">varname</i>.
If the optional <i class="arg">retvar</i> is not specified, then the value will be
returned as the result of the command. In this case, if key is not found
in the list, an error will result.</p>
<p>If <i class="arg">retvar</i> is specified and <i class="arg">key</i> is in the list, then the value
is returned in the variable <i class="arg">retvar</i> and the command returns 1 if the
key was present within the list. If <i class="arg">key</i> isn't in the list, the
command will return 0, and <i class="arg">retvar</i> will be left unchanged. If {} is
specified for <i class="arg">retvar</i>, the value is not returned, allowing the Tcl
programmer to determine if a <i class="arg">key</i> is present in a keyed list without
setting a variable as a side-effect.</p></dd>
<dt><a name="33"><b class="cmd">tsv::keylkeys</b> <i class="arg">varname</i> <i class="arg">keylist</i> <span class="opt">?key?</span></a></dt>
<dd><p>Return the a list of the keys in the keyed list <i class="arg">keylist</i> in the
shared variable <i class="arg">varname</i>. If <i class="arg">key</i> is specified, then it is
the name of a key field whose subfield keys are to be retrieved.</p></dd>
<dt><a name="34"><b class="cmd">tsv::keylset</b> <i class="arg">varname</i> <i class="arg">keylist</i> <i class="arg">key</i> <i class="arg">value</i> <span class="opt">?key value..?</span></a></dt>
<dd><p>Set the value associated with <i class="arg">key</i>, in the keyed list <i class="arg">keylist</i>
to <i class="arg">value</i>. If the <i class="arg">keylist</i> does not exists, it is created.
If <i class="arg">key</i> is not currently in the list, it will be added. If it already
exists, <i class="arg">value</i> replaces the existing value. Multiple keywords and
values may be specified, if desired.</p></dd>
</dl>
</div>
<div id="section6" class="doctools_section"><h2><a name="section6">DISCUSSION</a></h2>
<p>The current implementation of thread shared variables allows for easy and
convenient access to data shared between different threads.
Internally, the data is stored in Tcl objects and all package commands
operate on internal data representation, thus minimizing shimmering and
improving performance. Special care has been taken to assure that all
object data is properly locked and deep-copied when moving objects between
threads.</p>
<p>Due to the internal design of the Tcl core, there is no provision of full
integration of shared variables within the Tcl syntax, unfortunately. All
access to shared data must be performed with the supplied package commands.
Also, variable traces are not supported. But even so, benefits of easy,
simple and safe shared data manipulation outweighs imposed limitations.</p>
</div>
<div id="section7" class="doctools_section"><h2><a name="section7">CREDITS</a></h2>
<p>Thread shared variables are inspired by the nsv interface found in
AOLserver, a highly scalable Web server from America Online.</p>
</div>
<div id="see-also" class="doctools_section"><h2><a name="see-also">See Also</a></h2>
<p>thread, tpool, ttrace</p>
</div>
<div id="keywords" class="doctools_section"><h2><a name="keywords">Keywords</a></h2>
<p>locking, synchronization, thread shared data, threads</p>
</div>
</div></body></html>
