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.NET Forum / .NET Framework / CLR / December 2003Difference between CCW and CLR hosting
Hi. What is the difference between these two approaches? My thought is that CCW automatically loads the runtime, with default settings, while with CLR hosting you have control over each step of the runtime loading (type of GC and so on). Am I right? Have a nice day GV I think you've done a good job of outlinging some differences between the two features. What I'd like to point out is that these two features are often complimentary, and if you're hosting the runtime you'll be using both of them. So for example if you host the runtime any CCW's you use after you've loaded the runtime will use the runtime that you loaded with your hosted configuration. You'll also be using CCW's throughout the hosting process to get to the point where you run managed code. For example, when you make calls on an _AppDomain object in unmanaged code you'll be calling through a CCW. I'd also point out that if you loaded a CCW into your process, and then attempted to host the runtime, that you're not going to be able to load the runtime via the hosting APIs anymore (because the runtime is already loaded). If you attended the PDC and picked up the Whidbey bits you'll see a new API called LockClrVersion which allows a host to load the runtime before any other managed code gets run. So for example if someone tried to create a CCW in your process the host would be asked to start the runtime first. Finally, I'd like to point out that you might be able to get some of the same control via config files that you could over hosting. Certainly the hosting APIs give you more thorough control, but there is some overlap in what is exposed through config files. Unfortunately I'm not sure whether or not you can have config files associated with CCWs, but I imagine you could (sorry, I'm much more familiar with the hosting side than the CCW side of things). Hopefully this helps :) >-----Original Message----- >Hi. [quoted text clipped - 9 lines] >GV >. > I think you've done a good job of outlinging some > differences between the two features. What I'd like to [quoted text clipped - 9 lines] > you make calls on an _AppDomain object in unmanaged code > you'll be calling through a CCW. But in this case the runtime is already loaded. Am I correct? > I'd also point out that if you loaded a CCW into your > process, and then attempted to host the runtime, that [quoted text clipped - 6 lines] > to create a CCW in your process the host would be asked > to start the runtime first. Quite interesting. I think that CCW and CLR is sometimes confusing. I do not have access to Whidbey (at the moment), but I have a copy of Longhorn, so I'll have a look at it. Is this API documented on the longhorn SDK on the web? > Finally, I'd like to point out that you might be able to > get some of the same control via config files that you [quoted text clipped - 5 lines] > familiar with the hosting side than the CCW side of > things). Since you are "familiar" with CLR hosting, and maybe you are the right person to ask, why don't you (=MSFT) add some more documentation about CLR hosting? I haven't checked the Longhorn SDK, but the .NET 1.1 SDK documentation is quite poor in this field (and this somewhat strange, since there is a lot of stuff related to managed-unmanaged interaction). Have a nice day GV > Hopefully this helps :) > [quoted text clipped - 13 lines] > >GV > >. >> So for example if you host the runtime any CCW's you use >> after you've loaded the runtime will use the runtime that [quoted text clipped - 3 lines] >> you make calls on an _AppDomain object in unmanaged code >> you'll be calling through a CCW. > But in this case the runtime is already loaded. Am I correct? Yes, after you've loaded the runtime via the hosting interfaces you'll then be using the CCWs to call into the runtime. >> I'd also point out that if you loaded a CCW into your >> process, and then attempted to host the runtime, that [quoted text clipped - 11 lines] > I'll have a look at it. Is this API documented on the longhorn SDK on the > web? Unfortunately we haven't released our documentation for this feature yet (or any of the new hosting interfaces). It's a fairly simple API, and I'll give you a quick description here. In mscoree.h you'll find the definition of LockClrVersion. It takes 3 parameters, 1 function pointer, and 2 pointers to function pointers. You pass in a call back (hostCallback). mscoree will pass you back the begin/end setup pointers. mscoree will call hostCallback when someone wants to use managed code. During the callback the host performs the normal hosted CLR startup, but before they start the runtime they call the passed in pBeginHostSetup callback, and when they're done they call the pEndHostSetup callback. The callbacks & the starting of the runtime all need to occur on the same thread (this is how we know you're the one who should be starting the runtime, and that someone else isn't trying to sneak by it). You'll find that the callback function (FLockCllrVersionCallback) is defined in mscoree as well, takes no parameters, and returns an HRESULT. You'll want to return success (eg, S_OK, S_FALSE, etc...) from the callback to allow managed code to run, or failure if you don't want to allow it to run. > Since you are "familiar" with CLR hosting, and maybe you are the right > person to ask, why don't you (=MSFT) add some more documentation about CLR > hosting? I haven't checked the Longhorn SDK, but the .NET 1.1 SDK > documentation is quite poor in this field (and this somewhat strange, since > there is a lot of stuff related to managed-unmanaged interaction). I think the best documentation on this that we have today is http://www.gotdotnet.com/team/clr/about_clr_Hosting.aspx. There's white papers, specs on the interfaces, etc... I don't know if this is included in the SDK or not (and if not, why not), but I can bring this up to the PM in charge of this area. Have you seen this web page before? Do you think it gives a good description of the hosting? Or is there more that you'd like to hear about? And if so, what?
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