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Boost.Threadsscoped_timed_lock |
Introduction
Header
Synopsis
Members
Example
This class template defines a generic lock type which meets the
ScopedTimedLock requirements. The
timed_mutex and
recursive_timed_mutex classes use this template to
define their scoped_timed_lock
types.
Like all the Boost.Threads lock models,
scoped_timed_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_timed_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 TimedMutex 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 TimedMutex> class scoped_timed_lock : private boost::noncopyable // Exposition only. // Class scoped_timed_lock meets the NonCopyable requirement. { public: typedef TimedMutex mutex_type; scoped_timed_lock(TimedMutex& mx, const boost::xtime& xt); scoped_timed_lock(TimedMutex& mx, bool initially_locked); ~scoped_timed_lock(); void lock(); bool timed_lock(const xtime& xt); void unlock(); operator const void*() const; }; } // namespace thread } // namesapce detail } // namespace boost
scoped_timed_lock(TimedMutex& mx, const xtime& xt);
Effects: Associates mutex mx
with *this
.
Calls timed_lock
( xt
)
scoped_timed_lock(TimedMutex& mx, bool initially_locked);
Effects: Associates mutex mx
with *this
.
If initially_locked
is true
, calls lock()
.
~scoped_timed_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. Places the associated mutex in the locked state.
Throws: lock_error if locked()
or
as indicated in Effects.
bool timed_lock(const xtime& xt);
Effects: Same as lock()
, except that if xt is reached,
places the current thread in the Ready
state without further ado.
Returns: 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
.
#include <boost/thread/mutex.hpp> #include <iostream> int main(int, char*[]) { boost::timed_mutex mutex; boost::xtime xt; boost::get_xtime(&xt, boost::TIME_UTC); xt.sec += 1; boost::mutex::scoped_timed_lock scope_timed_lock(mutex, xt); if (scope_timed_lock.locked()) std::cout << "locked" << std::endl; else std::cout << "unlocked" << std::endl; return 0; }
The output is:
locked
Revised October 01, 2001
© Copyright William E. Kempf 2001 all rights reserved.