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Hi,
I have a VC++ COM Component that has to return array of long and array of strings to the C#. I Figure the way to do it is using SafeArrays for each of the arrays. I wanted a sample application that could return the arrays through the VC++ and then access the same arrays from the C#.
Pls I shall appreciate if some one could give a working sample.
Thanx.
Sheela
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So long as the array doesn't contain BOTH longs and strings, you could simply use UnmanagedType.LPArray (and associated properties) in the MarshalAsAttribute that you would use on your params. If you do need a SafeArray to return from your VC++ component, then you should take a look at Array Manipulation API Functions[^] which help you create SafeArrays in VC++. You declare your parameter in VC++ as SAFEARRAY and in C# using UnmanagedType.SafeArray and an object[] array.
The documentation for SafeArrays should give you plenty of examples and since this is VC++, I don't really want to type dozens of lines for something so trivial in higher-level languages (this isn't necessary a gripe against C/C++ - which I still enjoy and appreciate - just a fact). If your function was declared like so:
void SomeFunc(SAFEARRAY arr); ...then you could declare your C# method like so:
[DllImport("the name of your DLL")]
private static extern void SomeFunc(
[MarshalAs(UnmanagedType.SafeArray)] object[] arr);There are some other things you can do as well, but you should see the documentation for the MarshalAsAttribute class and the UnmanagedType enum in the .NET Framework SDK for more information.
Microsoft MVP, Visual C#
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Hello!
I want to write a C# spider which uses multiple threads that make synchronous HttpWebRequests to different sites. The big problem is that after a while (and it's a random period of time  ) the app. stops, more precisely all the Responses are TIMEOUT. The only solution seems to restart the application...some spider huh?
Other symptoms: I keep receiving a System.NullReferenceException in System.dll that I cannot catch, probably thrown by a thread from the Thread Pool (my guess);
- KeepAlive is set to false; Proxy is set by me;
- in machine.config maxconnections=100;
If I use only one thread and make one Request-Response (closing it of course) at a time it seems to work...but the one at a time approach is not what I want for my spider.
If you know something about this please help...thx!!!
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Instead of using Thread, you should try using a ThreadPool. This limits the number of threads that run and provides additional benefits. After the application spawns so many threads, it may appear to hang because the threads clog the system and keep the app very busy.
Also, many servers limit the number of connections per client. This is commonly configured at two connections. While all those requests are waiting, they will eventually timeout because only a couple will be able to get responses.
Microsoft MVP, Visual C#
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Thx for your response!
I'm thinking about the ThreadPool alternative.
If I run the app with 4 threads, I get the same result…after a while all the Responses are TIMEOUT and it’s not meter on witch server it's try to connect. I think the # of threads it’s not a problem, I think is something else…and what about the System.NullReferenceException in System.dll that I cannot catch?
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There could be a couple things happening. As I mentioned before, most servers limit the number of connections per client. This could cause a timeout because it won't respond to waiting requests.
Another problem is that you might not be locking your resources and are running into a dead-lock. If you have multiple threads accessing a resource, you should lock each thread so they don't access it concurrently (unless the object itself - like a synchronized Hashtable (see Hashtable.Synchronized) - is already thread-safe. You can do this easily in C# with the lock keyword. Typically, you can pass typeof(SomeClass) to lock against with multiple threads.
As far as the NullReferenceException thrown from a thread, you can handle the Application.ThreadException event or possibly the AppDomain.UnhandleException event.
Microsoft MVP, Visual C#
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Thx again for your answer!
I’ve consider the server limitation and my threads are one request - one server design to avoid this.
About the deadlock because of an object that threads share I’ve checked and it’s not that because are threads who are finishing their job and others are created (in a limit of course). The only problem is that all receive TIMEOUT.
I’ll give you an example…
I put the spider to get me the html content of the main page for 500 sites, 5 threads maxim at a time. TIMEOUT it’s set to 20 sec. For the first 100 sites it’s work ok, in generally, only a few timeout occurred, but after that it’s bad… this timeout’s keep appearing and after 350 all the responses are timeout…
I reverse the list and it’s the same. Some times, but very rarely, I receive some response till the spider finish the 500 list, but sporadic.
I don’t now what else to do…i've tried all
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You can't expect 500 threads to all run concurrently - the processor doesn't even allow this. You are familiar with time slices and the CPU, aren't you? Processes only get so much time. With that many threads, there's no way the CPU could service them all in a reasonable amount of time. That's why many web servers are multi-processor systems. You need to maintain better control of your threads.
If you look at the System.Threading namespace, you'll see several classes that can specify a timeout or wait indefinitely, but you should still avoid creating 500 threads. Consider designing your application so that you wait for threads to finish and then start another one. See the Threading[^] section in the .NET Framework SDK for information and examples.
Microsoft MVP, Visual C#
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I know, I'm not that crazy to put 500 threads at a time...
I only keep 5 of them at time, when one finish the callback function it’s “--“ the counter so another can be created an start a new request.
So you see why I think that the threads are not the issue here, it's something with the way framework manage the HttpWebRequests …
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If i create a library, and comment all public and protected members.
With the XML comments in C#.
Then the comments nicely pop up when im coding in other classes, or projects within the same solution that holds the project with the commented class.
But, when I now take the DLL, and reference not by project (not adding the project to my new solution), but by file reference, like how you would any third-party dll, the comments don't show up.
How do I tell the compiler to compile the xml comments into the dll. Or what do I have to do?
Thanks,
Kris.
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The XML document that contains the comments must be in the same directory as the assembly you're referencing.
Microsoft MVP, Visual C#
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Consider an array of some object like ClassA. How can I quickly iterate thru this array using unsafe code and pointers? Could you please provide me a sample code?
Don't forget, that's Persian Gulf not Arabian gulf!
Murphy:Click Here![^]
Events and Delegates simplified:Click Here![^]
I'm thirsty like sun, more landless than wind...
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I found this code:
using System;
class App {
unsafe static void Main() {
Int32[] arr = new Int32[] { 1, 2, 3, 4, 5 };
fixed (Int32* element = &arr[0]) {
for (Int32 x = 0, l = arr.Length; x <= l; x++) {
Console.WriteLine(element[x]);
}
}
}
}
I found it here[^], which I found as the first result by googling your words: "fast array iteration C# unsafe".
- Daniël Pelsmaeker
"All e-mail I send starts with a "Hello Colin" and ends with a suitable goodbye. I get some funny looks from people who aren't called Colin, but at least it's polite."
-David Wulff
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That's got to be the most useless code I've ever seen! Yeah, their using an unsafe context - but it's doing the same exact thing that the CLR would do in managed execution anyway. I doubt the performance payout is worth the lack of memory protection and the other problems you'll run into if this isn't run from the local machine (i.e., the MyComputer code group in reference to code access security).
Note - no offense meant to you. You simply re-posted this from a simple search result.
Microsoft MVP, Visual C#
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If your array contains objects then the best thing to use is a for loop. Unsafe code isn't going to help much.
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Is the object unmanaged? If not, it will be difficult. The GC is agnostic of pointers, so pointers are not allowed to reference types or structs that may appear (including structs with references) on the managed heap. If it were allowed, you could potentially wind up with heap resources referenced only by pointers that could be reclaimed while still in use.
From the language spec:
Unlike references (values of reference types), pointers are not tracked by the garbage collector - the garbage collector has no knowledge of pointers and the data to which they point. For this reason a pointer is not permitted to point to a reference or to a struct that contains references, and the referent type of a pointer must be an unmanaged-type.
An unmanaged-type is any type that isn't a reference-type and doesn't contain reference-type fields at any level of nesting. In other words, an unmanaged-type is one of the following:
sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, or bool.
The most exciting phrase to hear in science, the one that heralds the most discoveries, is not 'Eureka!' ('I found it!') but 'That's funny...’
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Suppose that I have an interface named IMyInterface and two classes both of which implement this interface, say ClassA and ClassB. Now I need a collection of these classes. So I have to have an array of IMyInterface(I don't want to use any thing like ArrayList or something). Now my problem is how to initiate this kind of array so that it would be able to hold both ClassA and ClassB? For example think I need an array of size 10:
private IMyInterface[] _interfaces;
_interfaces = new (what?)[10]
ps: What is the best way of having such a dynamic array? should I have a temp array and use .CopyTo method and re-new the old array?
Don't forget, that's Persian Gulf not Arabian gulf!
Murphy:Click Here![^]
Events and Delegates simplified:Click Here![^]
I'm thirsty like sun, more landless than wind...
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_interfaces = new IMyInterface[10];<br />
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You are right about interfaces = new IMyInterface[10];, but if I recall it correctly, the array is set to a size of 10, but contains NO values, not even null.
- Daniël Pelsmaeker
An egoist is someone who doesn't think about me.
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Interfaces are reference types, hence the array is filled with null. Try to call methods on any of those array elements (before initialization) and you'll get a NullReferenceException or ArgumentNullException depending on how you use the array elements. Step through in a debugger and you'll find that they're null as well. Structs and other value types - on the other hand, do not require instantiation in an array and their members will be the default values for whatever Types they are (reference types will still be null since you can't provide a default constructor with structs, but an Int32 will be 0, etc.).
Microsoft MVP, Visual C#
My Articles
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Each element of your array will be set to null. There is no such thing as NO value. Every reference type is initialized to null.
If you want dynamic array, you can use ArrayList() and just cast when you get elements:
ArrayList list = new ArrayList();
list.add(elem);
IMyInterface iface = (IMyInterface)list[i];
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hi,
i have a form(frmQueue) where i've put a datagrid control with only one column on it. when the user clicks on the "Update" button it gets whatever info from the datasource and displays it in the datagrid. the user can then select a particular column and click a "Get Details" button, when the button is clicked, i want the details to be displayed in textboxes in another form(frmTransaction). my question is how do i code the Get Details button. im new to this language...so an example would really get me working.
thx in advance
When a man's wife starts to understand him, she usually stops listening to him. 
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Change the constructor of your second form and add a srting parameter to it. And when you create it in your button event handler, pass he column name there and proccess it in second form.
Mazy
"A bank is a place that will lend you money if you can prove that you don't need it." - Bob Hope
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Hi Mazy,
When u said to pass the column name, did u mean the column name from the datasource or the datagrid?. i just wanna confirm.
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DataSource
Mazy
"A bank is a place that will lend you money if you can prove that you don't need it." - Bob Hope
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