C o rrect n e s s H a z a rd s in VS .NET

Encoder Code128 in VS .NET C o rrect n e s s H a z a rd s
C o rrect n e s s H a z a rd s
Make Code 128B In .NET Framework
Using Barcode creation for .NET Control to generate, create Code-128 image in .NET framework applications.
Since we already reviewed the basics of synchronization at the start of this book, let's look at some of the other variants on the core idea These include races caused by inconsistent use of locking in your program and not holding a lock long enough; we'll also see that certain kinds of benign race conditions are safe, can be useful, and do not result in incorrect program behavior
Code128 Recognizer In .NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
Inconsistent Synchronlzotlon
Barcode Creation In .NET Framework
Using Barcode creator for VS .NET Control to generate, create barcode image in .NET framework applications.
Assume you're using synchronization to ensure no threads see an object as it is undergoing a state transition It' s not good enough that access to this object is performed under the protection of just any kind of synchroniza tion You need to ensure that all threads access the object do so under the same kind of synchronization In other words, if you access some object x under lock a in one part of the program, and under lock b in another, those two parts of the program will not run mutually exclusive to one another This might be obvious, but this mistake is easy to make Often the results are just as bad as not having locked at all For example, consider this program snippet
Barcode Reader In .NET Framework
Using Barcode decoder for VS .NET Control to read, scan read, scan image in .NET applications.
stat ic static static stat i c Data s_x ; Data s y = ; obj ect s_loc kX new obj e ct ( ) ; object s_loc kY = new o b j e c t ( ) ;
Generating Code 128 Code Set C In C#.NET
Using Barcode encoder for .NET framework Control to generate, create USS Code 128 image in .NET applications.
= =
Code-128 Encoder In VS .NET
Using Barcode printer for ASP.NET Control to generate, create Code 128 image in ASP.NET applications.
void f O { loc k ( s_loc k X ) { s_x fl++ ; s_x f2++ ; }
Generate ANSI/AIM Code 128 In Visual Basic .NET
Using Barcode creation for .NET Control to generate, create Code 128A image in .NET framework applications.
void g ( )
Making Code 128B In VS .NET
Using Barcode generation for .NET Control to generate, create Code 128B image in Visual Studio .NET applications.
l o c k ( s_lo c kY ) { s y }
Print Bar Code In VS .NET
Using Barcode printer for .NET framework Control to generate, create bar code image in .NET framework applications.
new Data ( s_x ) ; II R e a d s state ( u n safely ) from s_x
Bar Code Creator In Visual Studio .NET
Using Barcode drawer for .NET Control to generate, create bar code image in VS .NET applications.
Now imagine that f and g are called on separate threads simultaneously Can you see the problem Even though both f and g execute under critical
UPC - 13 Printer In .NET
Using Barcode creator for .NET Control to generate, create EAN-13 Supplement 5 image in .NET framework applications.
C h a pter 11: C o n c u r re n cy H a z a rd s
Postnet Creation In .NET
Using Barcode encoder for .NET Control to generate, create Postnet 3 of 5 image in .NET framework applications.
regions, they d o so with different monitor objects: 5_1 o c kX and 5_1oc kY The result is that both methods run fully concurrent with one another, meaning that g may read state updates being made to 5_X by method f before they are complete Even if all g is doing is reading from the object, there could be some invariant protecting the relationship between fields f1 and f2 of Data instances And observing the broken invariants could lead to g crashing One of the most widely known dynamic race condition detection algo rithms, called the lock set algorithm, popularized by several research sys tems such as Eraser (see Further Reading, Savage, Burrows, Nelson, Sobalvarro) and RaceTrack (see Further Reading, Yu, Rodeheffer, Chen) looks for these kinds of inconsistent data protection races They even try to determine when a race is benign (ie, all shared accesses are reads) or a potential disaster An in-depth analysis of the algorithm itself is outside of the scope of this book, though interested readers might want to read more about it The basic idea is as follows: the system monitors all critical regions in the program and which memory locations are accessed under the pro tection of these critical regions during execution of the program The algo rithm uses this information to continuously refine its guess as to which locks are candidates for protecting particular memory locations It does so by taking the intersection of all locks held by a thread whenever a particu lar location was accessed In our above example, if one thread executed f first, the candidate set is { s_loc kX }; when g runs, it also gets a candidate set This set is { 5_1 o c kY }, which, when intersected with the previous set
EAN / UCC - 13 Generator In Java
Using Barcode drawer for Java Control to generate, create EAN-13 image in Java applications.
{ 5_1 o c kX } is the empty set The algorithm would thus (correctly) deter
Create UCC.EAN - 128 In VS .NET
Using Barcode maker for ASP.NET Control to generate, create UCC - 12 image in ASP.NET applications.
mine that there's a bug in the program shown There have been other recent approaches to solving this problem, includ ing static race condition detection For example, Abadi, et al (see Further Reading) proposed language extensions to associate locks with fields and to check that whenever a particular field was accessed the associated lock was held by the current thread Neither dynamic nor static race condition detection is broadly available in tools on the Windows platform today
Making UPC-A In .NET
Using Barcode maker for ASP.NET Control to generate, create UPC A image in ASP.NET applications.
Bar Code Encoder In .NET
Using Barcode encoder for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Barcode Drawer In .NET Framework
Using Barcode creator for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Decode Code 128 In .NET Framework
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET applications.