.NEt 2.0 : Threading questions

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Steve B. - 09 Feb 2007 10:04 GMT

Hi,

I'd like to know what is the difference between the class AutoResetEvent and
ManualResetEvent.

Actually, I want to use the WebClient.DownloadString method to download 8
files simultaneously in order to concatenate the content of the 8 files (no
matter in which order).
How can I do that ?
What are the available class to reach my goal ?

Is this code snippet the best way ?

StringBuilder sb;
public void Do(string[] urls)
{
WebClient wc = new WebClient();
sb = new StringBuilder();
wc.DownloadStringCompleted += new
DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);
AutoResetEvent[] threadSync = new AutoResetEvent[urls.Length];
for (int i = 0; i < urls.Length; i++)
{
threadSync[i] = new AutoResetEvent(true);
wc.DownloadStringAsync(
new Uri(urls[i]),
are
);
}
foreach (AutoResetEvent are in threadSync)
{
are.WaitOne();
}
context.Response.ContentType = "text/css";
}
private void wc_DownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e)
{
lock (sb)
{
sb.AppendLine(e.Result);
}
((AutoResetEvent)e.UserState).Set();
}

Thanks in advance,
Steve

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Michael Nemtsev - 09 Feb 2007 11:55 GMT

Hello Steve B.,

Read this article http://www.albahari.com/threading/part2.html#_Wait_Handles
where the difference with samples is described

S> I'd like to know what is the difference between the class
S> AutoResetEvent and ManualResetEvent

---
WBR, Michael Nemtsev [C# MVP]. Blog: http://spaces.live.com/laflour
team blog: http://devkids.blogspot.com/

"The greatest danger for most of us is not that our aim is too high and we
miss it, but that it is too low and we reach it" (c) Michelangelo

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Giulio Petrucci - 09 Feb 2007 12:01 GMT

Hi Steve

Steve B. ha scritto:

> I'd like to know what is the difference between the class AutoResetEvent and
> ManualResetEvent.

let's suppose you're waiting for an event to be set.
1) if it's an *Auto*ResetEvent, it will automatically reset itself as
you catch it's new state;

AutoResetEvent a = new AutoResetEvent(false);
...some code here...

a.WaitOne(); //here the execution stops until the event is not signaled
//here a's state is false;

2) if it's a *Manual*ResetEvent you must manually reset its state;

ManualResetEvent a = new ManualResetEvent(false);
...some code here...

a.WaitOne(); //here the execution stops until the event is not signaled
//here a's state is still true;
a.Reset();
//now it's false

HTH,
Giulio - Italia

--
OnAir: [nothing]

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Brian Gideon - 09 Feb 2007 14:10 GMT

> Hi,
>
> I'd like to know what is the difference between the class AutoResetEvent and
> ManualResetEvent.

Steve,

http://www.yoda.arachsys.com/csharp/threads/waithandles.shtml
http://www.albahari.com/threading/part2.html#_Wait_Handles

Brian

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Laura T. - 09 Feb 2007 14:19 GMT

In your case, I would not use so many AutoResetEvent objects. They consume
system resources and used this way, are quite inefficient, IMO.

You'd be better off with a simple counter and one event, EventWaitHandle.
Like:

long stillRunning;
EventWaitHandle finished = new EventWaitHandle(false,
EventResetMode.ManualReset);
StringBuilder sb;
public void Do(string[] urls)
{
WebClient wc = new WebClient();
sb = new StringBuilder(); // Should try to use new
StringBuilder(<estimate|guess "standard" dimension>)
wc.DownloadStringCompleted += new
DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);

for (int i = 0; i < urls.Length; i++)
{
Interloced.Increment(ref stillRunning);
wc.DownloadStringAsync(new Uri(urls[i]),are);
}

finished.WaitOne();
}

private void wc_DownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e)
{
lock (sb)
{
sb.AppendLine(e.Result);
}
// "Last one closes the door"
If(!Interlocked.Decrement(ref stillRunning)
finished.Set()
}

> Hi,
>
[quoted text clipped - 43 lines]
> Thanks in advance,
> Steve

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.NEt 2.0 : Threading questions

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