ASP.NET Web PDF Document Viewer/Editor Control Library

Transactions are always kicked off by a root object, which is a component flagged as either requiring a transaction or requiring a new transaction. This root object acts as the manager of the transaction, enlisting the appropriate set of autonomous methods to accomplish the transactional work. If any single method enlisted in the transaction votes no, the entire transaction is doomed to fail. All of the other objects enlisted in the transaction are called secondary objects. They need to be flagged with the Supports or Requires option. If they are flagged with Requires New, they become a new root object in a new transaction that will succeed or fail independently from the transaction that created it. This allows for a very flexible design of the transactions to reflect complex business processes (see Figure 7-7).

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ReportProgress: int -> unit DoWork: IEvent<DoWorkEventArgs> RunWorkerCompleted: IEvent<RunWorkerCompletedEventArgs> ProgressChanged: IEvent<ProgressChangedEventArgs>

The procedure do_or_insert inserts a given number of parent records and a given number of children for each parent record into the object view components_or_view: 54 55 56 57 58 59 60 61 62 63 64 65 66 67 procedure do_or_insert ( p_num_of_parents in int := 50, p_num_of_children in int := 500 ) as l_part_type_tab part_type_tab; l_part_type part_type; l_part_or_id number := 1; begin l_part_type_tab := part_type_tab(); l_part_type_tab.extend( p_num_of_children ); for i in 1..p_num_of_parents loop for j in 1..p_num_of_children loop

Note Objects such as a BackgroundWorker are two-faced : they have some methods and events that are for use from the main thread and some that are for use on the worker thread. This is common in concurrent programming. In particular, be careful to understand which thread an event is raised on. For BackgroundWorker, the RunWorkerAsync and CancelAsync methods are for use from the GUI thread, and the ProgressChanged and RunWorkerCompleted events are raised on the GUI thread. The DoWork event is raised on the worker thread, and the ReportProgress method and the CancellationPending property are for use from the worker thread when handling this event.

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Figure 7-7. A complex set of transactions, where one transaction failed and another succeeded, while a third component did its work outside of the context of any transaction

l_part_type_tab(j) := part_type( i, l_part_or_id, 'part'||i||j, 'part desc '||i||j ); l_part_or_id := l_part_or_id + 1; end loop; insert into components_or_view values ( i, 'component'||i, l_part_type_tab ); end loop; commit; end do_or_insert;

The members in Table 13-1 show two additional facets of BackgroundWorker objects: they can optionally support protocols for cancellation and reporting progress. To report progress percentages, a worker must simply call the ReportProgress method, which raises the ProgressChanged event in the GUI thread. For cancellation, a worker computation need only check the CancellationPending property at regular intervals, exiting the computation as a result.