Q3DeepCopy Class Reference [Qt3Support module]
The Q3DeepCopy class is a template class which ensures that implicitly shared and explicitly shared classes reference unique data. More...
#include <Q3DeepCopy> This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.
Note: All the functions in this class are reentrant.
Public Functions
Detailed Description
The Q3DeepCopy class is a template class which ensures that implicitly shared and explicitly shared classes reference unique data.
Normally, shared copies reference the same data to optimize memory use and for maximum speed. In the example below, s1, s2, s3, s4 and s5 share data.
QString s1 = "abcd";
QString s2 = s1;
QString s3 = s2;
QString s4 = s3;
QString s5 = s2;
Q3DeepCopy can be used several ways to ensure that an object references unique, unshared data. In the example below, s1, s2 and s5 share data, while neither s3 nor s4 share data.
QString s1 = "abcd";
QString s2 = s1;
Q3DeepCopy<QString> s3 = s2;
QString s4 = s3;
QString s5 = s2;
In the example below, s1, s2 and s5 share data, and s3 and s4 share data.
QString s1 = "abcd";
QString s2 = s1;
QString s3 = Q3DeepCopy<QString>( s2 );
QString s4 = s3;
QString s5 = s2;
Q3DeepCopy can also provide safety in multithreaded applications that use shared classes. In the example below, the variable global_string is used safely since the data contained in global_string is always a deep copy. This ensures that all threads get a unique copy of the data, and that any assignments to global_string will result in a deep copy.
Q3DeepCopy<QString> global_string;
QMutex global_mutex;
...
void setGlobalString( const QString &str )
{
global_mutex.lock();
global_string = str;
global_mutex.unlock();
}
...
void MyThread::run()
{
global_mutex.lock();
QString str = global_string;
global_mutex.unlock();
...
setGlobalString( str );
}
Warning: It is the application developer's responsibility to protect the object shared across multiple threads.
The examples above use QString, which is an implicitly shared class. The behavior of Q3DeepCopy is the same when using explicitly shared classes like QByteArray.
Currently, Q3DeepCopy works with the following classes:
See also Thread Support in Qt.
Member Function Documentation
Q3DeepCopy::Q3DeepCopy ()
Constructs an empty instance of type T.
Q3DeepCopy::Q3DeepCopy ( const T & t )
Constructs a deep copy of t.
Q3DeepCopy::operator T ()
Returns a deep copy of the encapsulated data.
Q3DeepCopy<T> & Q3DeepCopy::operator= ( const T & t )
Assigns a deep copy of t.
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