ASP.NET PDF Viewer using C#, VB/NET

PInvoke declarations are concise, but you must pay attention that for data types such as function pointers, parameter passing can be expensive. In general, libraries assume that crossing the language boundary causes a loss of efficiency and callbacks are invoked at a price different from ordinary functions. In this respect, the example represents a situation where the overhead of PInvoke is significant since a single call to transformArray causes a number of callbacks without performing any real computation into the native code.

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A connection cache is typically represented by an instance of a connection cache class that caches a group of pooled connection instances (remember, a pooled connection cache is associated with an actual physical database connection). The connection cache class extends the data source API. In Oracle9i, for a single connection cache instance, all the associated pooled connections must be physical connections to the same database and schema. In Oracle 10g, this restriction has been lifted in the new cache architecture.

As a more complicated example of PInvoke usage, in this section we show how to benefit from memory mapping into F# programs Memory mapping is a popular technique that allows a program to see a file (or a portion of a file) as if it was in memory, providing an efficient way to access files because the operating system uses the machinery of virtual memory for accessing files and significantly speeding up data access on files After proper initialization, which we will cover in a moment, the program obtains a pointer into the memory, and access to that portion of memory appears the same as accessing data stored in or into the file Memory mapping can be used both for reading and writing files, and every access performed into the memory is reflected into the corresponding position into the file.

In 10g, the restriction that all pooled connections associated with a cache must belong to same Tip

Component Services, or COM+, provides a rich set of features in a component-hosting environment, such as distributed transactions, just-in-time activation, object pooling, and asynchronously queued components. In 7, we examine these features in detail. Even though Component Services is a COM-based technology, Microsoft has added facilities to the .NET Framework that allow managed types to be easily configured for use within this environment. When you create .NET types that can be hosted under Component Services, they are called Serviced Components. Here s a logical view of an architecture that uses Serviced Components (see Figure 1-3). The critical feature of Component Services being leveraged from this architecture is its ability to automatically roll back transactions that span several data sources. Even if the data isn t hosted on the same server or on the same vendor platform, the Distributed Transaction Coordinator will automatically manage and then commit or roll back work that spans different data stores.

JDBC and Oracle Connection Caching Classes and Interfaces Standard JDBC Interfaces from the javax.sql Package Oracle JDBC Classes from the oracle.jdbc.pool Package OracleDataSource OracleConnectionCache

This is a typical sequence of system calls in order to map a file in memory: 1 A call to the CreateFile system call to open the file and obtain a handle to the file 2 A call to the CreateFileMapping system call to create a mapped file object 3 One or more calls to MapViewOfFile and UnmapViewOfFile to map and release portions of a file into memory In a typical usage, the whole file is mapped at once in memory 4 A call to CloseHandle to release the file The PInvoke interface to the required functions involves simple type mappings as is usual for Win32 API functions All the functions are in kernel32dll, and the signature can be found in the Windows SDK Listing 17-1 contains the definition of the F# wrapper for memory mapping.