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<html>
<head>
<meta http-equiv="Content-Type" content=
"text/html; charset=iso-8859-1">
<meta name="keywords" content="threads, BTL, thread library, C++">
<link rel="stylesheet" type="text/css" href="styles.css">
<title>Boost.Threads, recursive_mutex</title>
</head>
<body bgcolor="#FFFFFF" link="#0000FF" vlink="#800080">
<table summary="header" border="0" cellpadding="7" cellspacing="0" width="100%">
<tr>
<td valign="top" width="300">
<h3><img src="../../../c++boost.gif" alt="C++ Boost" width=
"277" height="86"></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Threads</h1>
<h2 align="center">recursive_mutex<br>
recursive_try_mutex<br>
recursive_timed_mutex</h2>
</td>
</tr>
</table>
<hr>
<p><a href="#Introduction">Introduction</a><br>
<a href="#Header">Header</a><br>
<a href="#recursive_mutex Synopsis">Class recursive_mutex
Synopsis</a><br>
<a href="#recursive_mutex Members">Class recursive_mutex
Members</a><br>
<a href="#recursive_try_mutex Synopsis">Class recursive_try_mutex
Synopsis</a><br>
<a href="#recursive_try_mutex Members">Class recursive_try_mutex
Members</a><br>
<a href="#recursive_timed_mutex Synopsis">Class recursive_timed_mutex
Synopsis</a><br>
<a href="#recursive_timed_mutex Members">Class recursive_timed_mutex
Members</a><br>
<a href="#Example">Example</a></p>
<h2><a name="Introduction">Introduction</a></h2>
<p>The <code>recursive_mutex</code>, <code>recursive_try_mutex</code>
and <code>recursive_timed_mutex</code> classes define full featured
models of the <a href="mutex_concept.html#Mutex">Mutex</a>, <a href=
"mutex_concept.html#TryMutex">TryMutex</a> and <a href=
"mutex_concept.html#TimedMutex">TimedMutex</a> concepts with recursive
locking semantics. These types should be used to synchronize access to
shared resources when recursive locking by a single thread is likely to
occur. A good example for this is when a class supplies "internal
synchronization" to ensure <a href="definitions.html#Thread-safe">
thread-safety</a> and a function of the class may have to call other
functions of the class which also attempt to lock the mutex. For
recursive locking mechanics, see <a href="mutex.html">mutexes</a>.</p>
<p>Each class supplies one or more typedefs for lock types which model
matching lock concepts. For the best possible performance you should
use the mutex class that supports the minimum set of lock types that
you need.</p>
<table summary="lock types" border="1" cellpadding="5">
<tr>
<td><b>Mutex Class</b></td>
<td><b>Lock name</b></td>
<td><b>Implementation defined Lock Type</b></td>
<td><b>Lock Concept</b></td>
</tr>
<tr>
<td valign="top"><a href="#recursive_mutex Synopsis"><code>
recursive_mutex</code></a></td>
<td valign="middle"><code>scoped_lock</code></td>
<td valign="middle"><a href="scoped_lock.html"><code>
detail::thread::scoped_lock<recursive_mutex></code></a></td>
<td valign="middle"><a href="lock_concept.html#ScopedLock">
ScopedLock</a></td>
</tr>
<tr>
<td valign="top"><code><a href="#recursive_try_mutex Synopsis">
recursive_try_mutex</a></code></td>
<td valign="middle"><code>scoped_lock<br>
scoped_try_lock</code></td>
<td valign="middle"><a href="scoped_lock.html"><code>
detail::thread::scoped_lock<recursive_try_mutex><br>
</code></a> <code><a href="scoped_try_lock.html">
detail::thread::scoped_try_lock<recursive_try_mutex></a></code></td>
<td valign="middle"><a href="lock_concept.html#ScopedLock">
ScopedLock</a><br>
<a href="lock_concept.html#ScopedTryLock">
ScopedTryLock</a></td>
</tr>
<tr>
<td valign="top"><code><a href=
"#recursive_timed_mutex Synopsis">
recursive_timed_mutex</a></code> </td>
<td valign="middle"><code>scoped_lock<br>
scoped_try_lock<br>
scoped_timed_lock</code></td>
<td valign="middle"><a href="scoped_lock.html"><code>
detail::thread::scoped_lock<recursive_timed_mutex></code></a><br>
<a href="scoped_try_lock.html"><code>
detail::thread::scoped_try_lock<recursive_timed_mutex></code></a><br>
<a href="scoped_timed_lock.html"><code>
detail::thread::scoped_timed_lock<recursive_timed_mutex></code></a></td>
<td valign="middle"><a href="lock_concept.html#ScopedLock">
ScopedLock</a><br>
<a href="lock_concept.html#ScopedTryLock">
ScopedTryLock</a><br>
<a href="lock_concept.html#ScopedTimedLock">
ScopedTimedLock</a></td>
</tr>
</table>
<p>The <code>recursive_mutex</code>, <code>recursive_try_mutex</code>
and <code>recursive_timed_mutex</code> employ a <code>Recursive</code>
<a href="mutex_concept.html#LockingStrategies">locking strategy</a>, so
attempts to recursively lock them succeed and an internal "lock
count" is maintained. Attempts to unlock them by a thread that
does not own a lock on them will result in a <a href="lock_error.html">
lock_error</a> exception being thrown.</p>
<p>The <code>recursive_mutex</code>, <code>recursive_try_mutex</code>
and <code>recursive_timed_mutex</code> leave the <a href=
"mutex_concept.html#SchedulingPolicies">scheduling policy</a> as <code>
Unspecified</code>. Programmers should assume that threads waiting for
a lock on objects of these types acquire the lock in a random order,
even though the specific behavior for a given platform may be
different.</p>
<h2><a name="Header">Header</a></h2>
<pre>
#include <a href=
"../../../boost/thread/recursive_mutex.hpp"><boost/thread/recursive_mutex.hpp></a>
</pre>
<h2>Class <a name="recursive_mutex Synopsis">recursive_mutex
Synopsis</a></h2>
<hr>
<pre>
namespace boost
{
class recursive_mutex : private <a href=
"../../utility/utility.htm">boost::noncopyable</a> // Exposition only.
// Class recursive_mutex meets the <a href=
"overview.html#NonCopyable">NonCopyable</a> requirement.
{
public:
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_lock;
recursive_mutex();
~recursive_mutex();
};
}
</pre>
<h2>Class <a name="recursive_mutex Members">recursive_mutex
Members</a></h2>
<hr>
<h3>Constructor</h3>
<pre>
recursive_mutex();
</pre>
<p><b>Postconditions:</b> <code>*this</code> is in the unlocked
state.</p>
<hr>
<h3>Destructor</h3>
<pre>
~recursive_mutex();
</pre>
<p><b>Requires:</b> <code>*this</code> is in the unlocked state.</p>
<p><b>Effects:</b> Destroys <code>*this</code>.</p>
<p><b>Dangers:</b> Destruction of a locked mutex is a serious
programming error resulting in undefined behavior such as a program
crash..</p>
<hr>
<h2>Class <a name="recursive_try_mutex Synopsis">recursive_try_mutex
Synopsis</a></h2>
<pre>
namespace boost
{
class recursive_try_mutex : private boost::noncopyable // Exposition only.
// Class recursive_try_mutex meets the <a href=
"overview.html#NonCopyable">NonCopyable</a> requirement.
{
public:
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_lock;
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_try_lock;
recursive_try_mutex();
~recursive_try_mutex();
};
}
</pre>
<h2>Class <a name="recursive_try_mutex Members">recursive_try_mutex
Members</a></h2>
<hr>
<h3>Constructor</h3>
<pre>
recursive_try_mutex();
</pre>
<p><b>Postconditions:</b> <code>*this</code> is in the unlocked
state.</p>
<hr>
<h3>Destructor</h3>
<pre>
~recursive_try_mutex();
</pre>
<p><b>Requires:</b> <code>*this</code> is in the unlocked state.</p>
<p><b>Effects:</b> Destroys <code>*this</code>.</p>
<p><b>Dangers:</b> Destruction of a locked mutex is a serious
programming error resulting in undefined behavior such as a program
crash..</p>
<hr>
<h2>Class <a name="recursive_timed_mutex Synopsis">
recursive_timed_mutex Synopsis</a></h2>
<pre>
namespace boost
{
class recursive_timed_mutex : private boost::noncopyable // Exposition only.
// Class recursive_timed_mutex meets the <a href=
"overview.html#NonCopyable">NonCopyable</a> requirement.
{
public:
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_lock;
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_try_lock;
typedef <i>[implementation defined; see <a href=
"#Introduction">Introduction</a>]</i> scoped_timed_lock;
recursive_timed_mutex();
~recursive_timed_mutex();
};
}
</pre>
<h2>Class <a name="recursive_timed_mutex Members">recursive_timed_mutex
Members</a></h2>
<hr>
<h3>Constructor</h3>
<pre>
recursive_timed_mutex();
</pre>
<p><b>Postconditions:</b> <code>*this</code> is in the unlocked
state.</p>
<hr>
<h3>Destructor</h3>
<pre>
~recursive_timed_mutex();
</pre>
<p><b>Requires:</b> <code>*this</code> is in the unlocked state.</p>
<p><b>Effects:</b> Destroys <code>*this</code>.</p>
<p><b>Dangers:</b> Destruction of a locked mutex is a serious
programming error resulting in undefined behavior such as a program
crash..</p>
<hr>
<h2><a name="Example">Example</a> Usage</h2>
<pre>
#include <a href=
"../../../boost/thread/recursive_mutex.hpp"><boost/thread/recursive_mutex.hpp></a>
#include <a href=
"../../../boost/thread/thread.hpp"><boost/thread/thread.hpp></a>
#include <iostream>
class counter
{
public:
counter() : count(0) { }
int add(int val) {
boost::recursive_mutex::scoped_lock scoped_lock(mutex);
count += val;
return count;
}
int increment() {
boost::recursive_mutex::scoped_lock scoped_lock(mutex);
return add(1);
}
private:
boost::recursive_mutex mutex;
int count;
};
counter c;
void change_count(void*)
{
std::cout << "count == " << c.increment() << std::endl;
}
int main(int, char*[])
{
const int num_threads=4;
boost::thread_group threads;
for (int i=0; i < num_threads; ++i)
threads.create_thread(&change_count, 0);
threads.join_all();
return 0;
}
</pre>
<p>The output is:</p>
<pre>
count == 1
count == 2
count == 3
count == 4
</pre>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->05 November, 2001<!--webbot bot="Timestamp" endspan i-checksum="39359" --></p>
<p><i>© Copyright <a href="mailto:williamkempf@hotmail.com">
William E. Kempf</a> 2001 all rights reserved.</i></p>
</body>
</html>
|
