.NET/ASP.NET/C#/VB.NET PDF Document SDK

The second issue is the index used for writing to the buffer Because there might be several producers updating the buffer, they must share an index that must be protected by a mutex Let s have a look at the updated run methods starting with the TextProducer class (see Listing 12-22) The highlighted lines show the shared index variable, index, and its mutex, indexMutex The mutex is locked and unlocked around the line containing index++ That is the only place where index is referenced and updated You cannot use a QMutexLocker here because that would lock the mutex in the entire run method and block the other producer threads Instead, the mutex must be locked for the shortest possible period Listing 12-22 The TextProducer run method, updated for handling several simultaneous producers void TextProducer::run() { static int index = 0; static QMutex indexMutex; for( int i=0; i<m_text.

excel barcode erstellen freeware, how to barcode in excel 2010, excel 2003 barcode add in, barcode font for excel mac, barcode wizard excel, barcode generator excel download, excel 2010 barcode macro, free barcode add in for excel 2013, install barcode font in excel 2010, barcode excel 2013 download,

}

}

} Console.WriteLine("Leaving main loop");

length(); ++i ) { freeSpaceacquire(); indexMutexlock(); buffer[ index++ % bufferSize ] = m_text[ i ]; indexMutexunlock(); if( i == m_textlength()-1 ) atEndacquire();.

Here s the output:

If the current record is the first one in the record set, then you cannot move to the previous record, and this will be false; otherwise, it will be true This is a SysDataDataTable that contains the complete set of data that is currently loaded into the ListView control This is returned by a select query against the underlying data source Specifies the index of the currently selected item in the data source Specifies the currently selected row on the data source Specifies the number of rows in the data table within the data property As this control renders a range of items, you can create a different style for alternating rows, giving a striped appearance that makes it easier to distinguish the data from different rows You specify that using a CSS class with this property This specifies how the range of items will be laid out.

Calling AddNumbers Starting main loop Starting AddNumbers In AddNumbers: Swing Dancing at the South Bank In main loop: 0: Swing Dancing at the South Bank In AddNumbers: Saturday Night Swing In main loop: 1: Saturday Night Swing In AddNumbers: Formula 1 German Grand Prix In main loop: 2: Formula 1 German Grand Prix In AddNumbers: Swing Dance Picnic In main loop: 3: Swing Dance Picnic In AddNumbers: Stompin' at the 100 Club In main loop: 4: Stompin' at the 100 Club Leaving AddNumbers Leaving main loop

Even though the main method calls AddNumbers only once, before the start of the loop, you can see from the output that the code flits back and forth between the main loop and AddNumbers for each item in the list. That s how yield return works it returns from the method temporarily. Execution will continue from after the yield return as soon as the code consuming the collection asks for the next element. (More precisely, it will happen when the client code calls MoveNext on the enumerator.) C# generates some code that remembers where it had got to on the last yield return so that it can carry on from where it left off.

availableData.release(); } } The run method of the TextConsumer class has been only marginally updated. The highlighted line in Listing 12-23 shows how the atEnd semaphore is used in the while loop. Compare this with Listing 12-20, in which atEnd is a flag. Listing 12-23. The TextConsumer run method, updated for handing several simultaneous producers void TextConsumer::run() { int i = 0; while( atEnd.available() || availableData.available() ) { availableData.acquire(); qDebug() << buffer[ i ]; i = (i+1) % bufferSize; freeSpace.release(); } } Notice that the actual interaction between the producers and the consumer using the semaphores for available data and free space is unchanged when comparing the single producer and multiple producer versions. Listing 12-24 shows a main function setting up two producers and a consumer. The producers and consumer are set up and started; then the function waits for them to finish just as in the single producer version. Listing 12-24. A main function with two producers and one consumer int main( int argc, char **argv ) { QApplication app( argc, argv ); TextProducer p1( "this text is written using lower case characters." "it will compete with text written using upper case characters." ); TextProducer p2( "THIS TEXT IS WRITTEN USING UPPER CASE CHARACTERS!" "IT WILL COMPETE WITH TEXT WRITTEN USING LOWER CASE CHARACTERS!" ); TextConsumer consumer; p1.start(); p2.start(); consumer.start(); p1.wait(); p2.wait();

You might be wondering what happens if the consumer abandons the loop halfway through. If that happens, execution will not continue from the yield return. However, as you saw in Example 7-30, code that consumes an enumeration should have a using statement to ensure that the enumerator is always disposed of a foreach loop will always do this for you. The enumerator generated by C# to implement yield return relies on this to ensure that any using or finally blocks inside your enumerator method run correctly even when the enumeration is abandoned halfway through. This causes a slight wrinkle in the story regarding exception handling. You ll find that you cannot use yield return inside a try block that is followed by a catch block, for example, because it s not possible for the C# compiler to guarantee that exceptions will be handled consistently in situations where enumerations are abandoned.