code 128 c# font Synchronization Lock Exception in C#

Encoding Code 128C in C# Synchronization Lock Exception

Synchronization Lock Exception
Generating USS Code 128 In Visual C#.NET
Using Barcode generator for Visual Studio .NET Control to generate, create Code128 image in .NET applications.
www.OnBarcode.com
Code128 Reader In C#.NET
Using Barcode reader for .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
A synchronization lock exception is thrown whenever an attempt is made to invoke Pulse or Wait without having first acquired a lock.
Paint Barcode In Visual C#.NET
Using Barcode drawer for .NET framework Control to generate, create Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Generating QR Code In C#.NET
Using Barcode creator for .NET Control to generate, create QR image in Visual Studio .NET applications.
www.OnBarcode.com
We ve seen how a single thread can be controlled using Pulse; now we ll examine how multiple threads can respond to PulseAll. 7.4.4 The PulseAll method Suppose that you receive a phone call from a client or supervisor wanting to know if all of the organization s web sites are functioning properly. Rather than wait for the next polling interval, you would like to check the sites immediately. One way to do this is to use Thread.Interrupt. This triggers an interrupt on the thread that it is associated with the instance of the Thread object on which it is invoked. Each thread would need to be interrupted. Similarly, the Pulse and Wait approach we covered in the last chapter could be used. Instead of having a Thread.Sleep statement, you would have a Monitor.Wait statement. Unless the object that is being waited on is pulsed, Wait with a timeout value functions like the Sleep method:
Encoding Matrix 2D Barcode In C#
Using Barcode creator for VS .NET Control to generate, create 2D Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
Encode EAN 13 In Visual C#
Using Barcode encoder for .NET Control to generate, create GS1 - 13 image in Visual Studio .NET applications.
www.OnBarcode.com
Thread.Sleep(mSleepTime)
Generating 1D In Visual C#
Using Barcode creator for VS .NET Control to generate, create Linear 1D Barcode image in .NET framework applications.
www.OnBarcode.com
Print USPS Intelligent Mail In Visual C#
Using Barcode generator for .NET framework Control to generate, create USPS Intelligent Mail image in .NET applications.
www.OnBarcode.com
Thread.Sleep can be replaced with the following lines:
Code 128 Code Set C Reader In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Read ANSI/AIM Code 128 In VB.NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
SyncLock WaitLockObject Monitor.Wait(WaitLockObject, mWaitTime) End SyncLock
Creating ANSI/AIM Code 128 In Objective-C
Using Barcode maker for iPad Control to generate, create USS Code 128 image in iPad applications.
www.OnBarcode.com
Generating UPC-A Supplement 2 In VS .NET
Using Barcode creator for ASP.NET Control to generate, create Universal Product Code version A image in ASP.NET applications.
www.OnBarcode.com
WaitLockObject is a shared/static object. Recall from the last section that in order to Wait on an object the thread must first enter a synchronized region of code. One way to do this is to use the SyncLock statement. This is equivalent to calling Monitor.Enter and Monitor.Exit. Since WaitLockObject is shared/static, there is only one instance of it for all instances of the WebSiteMonitor class. To signal those threads waiting for the lock, we use the PulseAll method which alerts all threads waiting on a lock that the state of the object has changed and that they should resume processing. The differences between Pulse and PulseAll are shown in figure 7.18. PulseAll empties the waiting queue, moving all entries into the ready queue. As soon as each of the threads in the ready queue are able to reacquire the lock, they begin executing. Wait, Pulse, and PulseAll can only be called successfully if the synchronization lock around them locks on the same object that is passed in as the parameter. The following example demonstrates the incorrect way to call PulseAll:
Barcode Drawer In Java
Using Barcode printer for Java Control to generate, create Barcode image in Java applications.
www.OnBarcode.com
UPC Symbol Printer In .NET
Using Barcode drawer for Visual Studio .NET Control to generate, create GTIN - 12 image in .NET applications.
www.OnBarcode.com
CONCURRENCY CONTROL
Reading Code 39 Full ASCII In Visual C#.NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in Visual Studio .NET applications.
www.OnBarcode.com
GTIN - 13 Recognizer In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
The difference between Pulse and PulseAll
Data Matrix 2d Barcode Generator In None
Using Barcode creation for Online Control to generate, create DataMatrix image in Online applications.
www.OnBarcode.com
Decoding Universal Product Code Version A In .NET Framework
Using Barcode scanner for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
SyncLock LockObjectOne Try Monitor.PulseAll(LockObjectTwo) Catch ex As Exception MsgBox(ex.Message) End Try End SyncLock
Barcode Decoder In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
www.OnBarcode.com
Creating PDF 417 In None
Using Barcode creation for Microsoft Excel Control to generate, create PDF417 image in Office Excel applications.
www.OnBarcode.com
Notice that the SyncLock is performed on LockObjectOne while PulseAll uses LockObjectTwo. This causes a SynchronizationLockException to be raised. The correct code is:
SyncLock LockObjectThree Try Monitor.Wait(LockObjectThree) MsgBox("Good Thread After Wait") Catch ex As Exception MsgBox(ex.Message) End Try End SyncLock
DIGGING DEEPER INTO
CONCURRENCY CONTROL
There is much more to currency control than the basics we ve covered so far. In this section we cover those elements that are a little less frequently used.
C# s volatile keyword This topic is restricted to C#. VB.NET does not support the volatile keyword. Not to worry, very few situations require its use. In general it is easier to use the other synchronization mechanisms we ve covered in this chapter. This topic is covered for completeness.
The Volatile Keyword
Volatile is a hint to the compiler that a value may change without its knowledge and that it should not make assumptions regarding the value during optimization.
The most important thing to know about a volatile field is that it is not thread-safe. If two threads attempt to update a volatile field at the same time, bad things will DIGGING DEEPER INTO CONCURRENCY CONTROL 137
likely happen. By using the volatile statement you re telling the compiler that this variable s value may change in an unforeseen way. This keeps the compiler from optimizing instructions that access the variable.
GUIDELINES
Making a field volatile does not make it thread-safe. All fields enclosed in a synchronization block and accessed by multiple threads should be volatile. A volatile field cannot be passed as a reference. This means that an interlocked method cannot be used with a volatile field.
Compilers often perform optimizations to increase performance. One of the ways it optimizes is by placing frequently used variables into registers. A register is a location in the processor that can be accessed quickly. Once the value is in the register, the compiler assumes that nothing else changes the value of the variable. This means the generated code only accesses main memory when it knows it needs to retrieve the value. In the case of multithreaded applications, a different thread may change the value after the optimized code has read it in. The optimized code might not notice the change in the value. Listing 7.13 demonstrates the use volatile.
Listing 7.13 The use of the volatile keyword (C#)
private volatile int CurrentThreadCode; . . . System.Random rnd = new System.Random(); int RandomIndex; int TickCount; do RandomIndex= rnd.Next(NumberOfListeningThreads); while (CurrentRandomIndex ==RandomIndex); CurrentRandomIndex =RandomIndex; TickCount =Environment.TickCount; CurrentThreadCode = ListeningThreads[RandomIndex].GetHashCode(); . . . while(true) { if (CurrentThreadCode == MyId) { . . .
One form of optimization that causes multithreaded applications grief is reordering instructions. This makes most developers a little nervous. We like to think that if we do an assignment and then a test that the test instruction will always occur after the assignment. Some processors reorder instructions. Those processors are smart enough to do this in such a way that the outcome of the program is the same as if the instructions had not been reordered.
Copyright © OnBarcode.com . All rights reserved.