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New Message on BDOTNET
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From: Sitaraman
Message 1 in Discussion
Hi All Was trying the lock and Monitor.Enter/Exit and have a few doubts in that.
lets say i have a class which has a static method. Now this static method increments a
static counter variable. Multiple Threads access this method. I want to have thread
safety. I use either the lock keyword or the Monitor Enter/Exit methods. The
code(using lock keyword) is as follows using System;
using System.Threading; public class StaticThreads
{
public static String strCounter="0";
public static int intCounter=0; public static void Main()
{
Thread myThread1 = new Thread(new
ThreadStart(StaticThreads.DoSomething));
Thread myThread2 = new Thread(new
ThreadStart(StaticThreads.DoSomething));
myThread1.Name = "Thread 1";
myThread2.Name = "Thread 2";
Console.WriteLine("Press ENTER to start,");
Console.WriteLine("and ENTER again to stop.");
Console.ReadLine();
myThread1.Start();
myThread2.Start();
Console.ReadLine();
myThread1.Abort();
myThread2.Abort();
}
public static void DoSomething()
{
while (true)
{
lock(typeof(StaticThreads))//Acquiring a lock
{
//declare a local variable
String i1;
// get counter value, increment and store it in local var(not set in
static var yet)
i1=Convert.ToString((Convert.ToInt16(StaticThreads.strCounter)+1));
// Wait. equivalent to some processing in real world
Thread.Sleep(1000);
// Setting the new value in the static variable
StaticThreads.strCounter=i1;
// printing the modified counter value
Console.WriteLine(Thread.CurrentThread.Name + " New Counter Value : " +
StaticThreads.strCounter );
} // releasing the lock
}
}
} My questions are Why do i have to pass typeof(StaticThreads) and not
pass just StaticThreads.strCounter. Is it coz of the fact that DoSomething() is a
static method. how does it make a difference. Also wat is the impact on performance
when i pass typeof. Is the duration of the lock lengthier in the case of passing
typeof(StaticThreads)
I tried the above code using Monitor.Enter/Exit methods. the output is same.
Even MSDN says that lock and Monitor.Enter/Exit is precisely equivalent "except that
passed object parameter is only evaluated once". What does this mean. What is the
impact
Why is that these mechanisms take only reference type parameter and not value
type parameter. is it basically to avoid performance overhead which would be there
due to boxing/unboxing. If i do want to pass a value type, do i have to have a
wrapper object on such value types for passing to these mechanisms. Also the error on
passing value types to these mechanisms are quite weird. Whereas lock gives me a
compiler error when a value type is passed, the Monitor.nter and Exit gives me
Runtime Exception (" System.Threading.SynchronizationLockException"). Why is this so?
regards, sr p.s. 1) i do not want ro use singleton(as the example is the
standard one for singleton mechanisms) 2) i have already checked the C# Language
Specification 8.12 The lock statement (just in case one of u pt me to tht :) )
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