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Boost.Threadsscoped_lock |
Introduction
Header
Synopsis
Members
Example
This class template defines a generic lock type which meets the
ScopedLock requirements. The
mutex, try_mutex,
timed_mutex, recursive_mutex,
recursive_try_mutex and
recursive_timed_mutex classes all use this template
to define their scoped_lock
types.
Like all the Boost.Threads lock models,
scoped_lock
objects are meant to be short-lived. Objects of the class
are not thread-safe, and so should not be
shared between threads.
Class scoped_lock
follows the "resource acquisition is
initialization" idiom [Stroustrup
00 14.4.1] and is a realization of the "Scoped Locking Pattern"
[Schmidt-00]. Thus the usage is to let the
constructor do the locking, and then let the destructor do the unlocking automatically at
the end of the enclosing scope. The lock() and unlock() members are usually not
explicitly called, but are provided to allow for complex overlapping locks of multiple
mutexes.
The type used to instantiate the class must meet the Mutex requirements.
Although this class is an implementation detail, it is publicly documented here because of its importance.
#include <boost/thread/detail/lock.hpp> This header is usually not included directly by programmers because it is supplied by <boost/thread/mutex.hpp> or <boost/thread/recursive_mutex.hpp>
namespace boost { namespace detail { namespace thread { template <typename Mutex> class scoped_lock : private boost::noncopyable // Exposition only. // Class scoped_lock meets the NonCopyable requirement. { public: typedef Mutex mutex_type; explicit scoped_lock(Mutex& mx, bool initially_locked=true); ~scoped_lock(); void lock(); void unlock(); operator const void*() const; bool locked() const; }; } // namespace thread } // namespace detail } // namespace boost
explicit scoped_lock(Mutex& mx, bool initially_locked=true);
Effects: Associates mutex mx
with *this
.
If initially_locked
is true,
calls lock()
.
~scoped_lock();
Effects: If locked()
, calls unlock()
. Destroys
*this
.
void lock();
Effects: If the associated mutex is already locked by another lock in the current thread, the effects depend on the locking strategy of the associated mutex, as shown in the following table:
Locking Strategy of associated mutex |
Effect if associated mutex is already locked by the current thread |
Recursive | As if an additional lock were added to the mutex. |
Checked | Throws lock_error. |
Unchecked | Undefined behavior [ISO 1.3.12] (but typically, deadlock.) |
If the associated mutex is already locked by some other thread, places the current thread in the Blocked state until the associated mutex is unlocked, after which the current thread is placed in the Ready state, eventually to be returned to the Running state.
Postcondition: locked()
Throws: lock_error if locked()
or
as indicated in Effects.
void unlock();
Effects: Unlocks the associated mutex.
Throws: lock_error if !locked()
.
operator const void*() const;
Returns: If the associated mutex is currently locked, a value convertible to
true
, else a value convertible to false
.
Rationale: A const void*
conversion is considered safer than a
conversion to bool
.
bool locked() const;
Returns: this->operator const void*() != 0
.
See the example given in the documentation for the mutex class.
Revised 01 October, 2001
© Copyright William E. Kempf 2001 all rights reserved.