September 2001
Intermediate to advanced
384 pages
11h 59m
English
Content preview from COM & .NET Component ServicesBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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The Call Object
In addition to
providing a context object to represent the context of an object,
COM+ creates a transient object called the call
object each time that object is called. The transient call
object represents the current call in progress. Objects can access
their call object by calling CoGetCallContext( )
(see Figure 2-6). The CoGetCallContext( ) signature is defined as:
HRESULT CoGetCallContext(REFIID riid, void** ppInterface);
The call object only exists as long as a call from a client is in
progress, and it is destroyed by COM+ after the called method
returns. You should not cache a pointer to the call object as a
member variable of your object because that pointer will be invalid
once the method that saved it returns. Furthermore, if your object is
doing work in the background—that is, no method call from the
client is currently in progress—it will not have access to a
call object. If you try to access a call object while a call is not
in progress, CoGetCallContext( ) will fail and
return the error code
RPC_E_CALL_COMPLETE
. You can, however, still access the
context object, which exists as long as the context exists, and whose
pointer can be cached by the objects associated with it.
The call object exposes two interfaces used to obtain information
about the call security settings. These interfaces, discussed in
Chapter 7, are
ISecurityCallContext
and
IServerSecurity
.
Figure 2-6. When a method call is in progress, a COM+ object has access to the call object ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.