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Global RWLock with Global Mutex to Protect Salaries in .NET Attach DataMatrix in .NET Global RWLock with Global Mutex to Protect Salaries




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Global RWLock with Global Mutex to Protect Salaries generate, create ecc200 none on .net projects QR Code Safty Version two of the p .NET ECC200 rogram uses a readers/writer lock to protect the list and a mutex to protect the salaries. This way, any number of threads can run down the list, at the same time searching for people to receive raises.

Once found, we need to protect the salary data while we update it. We add the SalaryLock for this purpose. Clearly, we could not update the salary if we only held a read lock.

When a thread wishes to remove one of Dan"s enemies from the list, that thread must hold a writer lock while it searches down the list and removes the offending element (see Figure 12-6). Figure 12-6. Friends/Enemies: Global RWlock and Salary Lock.

It"s important for u s to think very carefully about what each lock is protecting. The RWlock protects the list structures and the pointers. It does not protect the salaries.

Surprisingly, the performance of this code is not much better than that of the previous code! Inspecting the code closely, you should realize that very little time is spent actually searching down the list (about 1 s per element). It is the contention for the salary lock when the delay is non-zero that takes all the time. Once again, no thread may hold a pointer to any portion of the list unless it owns one of the locks.

. Code Example 12-4 is barcode data matrix for .NET the code that updates the salary of Bil"s friends. The delay is inside the critical section; thus, while one thread is sleeping here, all the other threads must wait outside.

Moving the delay outside would vastly increase the performance of the program. It wouldn"t be terribly realistic to do so. As the delay represents a write to disk or some other operation on the salary, it really must be inside the critical section.

Example 12-4 : giveRaise() (listGlobaRW.java). public synchronized void giveRaise() { rwlock.unlock(); salary++; delay(raiseDelay); }. Note that we release .NET DataMatrix the RWlock as soon as we obtain the salary lock, allowing liquidator threads to begin their searches. The liquidator threads are allowed to run while we"re updating the salary! To make this work correctly, the function liquidatePerson() must also lock the salary lock before it changes anything in the object (Code Example 12-5).

Also notice how we are mixing our RWlocks with Java"s synchronized sections. Example 12-5 Removing an Element from the List (ListGlobalRW2.java).

public synchronized void liquidate() { next = next.next; rwlock.unlock(); delay(liquidateDelay); }.

Global RWLock with Local Mutex to Protect Salaries Version three of the program (Figure 12-7) uses a readers/writer lock to protect the list and a local mutex to protect individual salaries. This way, any number of threads can run down the list searching for people to give raises to at the same time. Once found, we need to protect the individual salary data while we update it.

Now we have overcome the major bottleneck of this program. Many threads may now update different salaries at the same time. Figure 12-7.

Friends/Enemies: Global RWlock and Local Salary Lock. Once again, no threa barcode data matrix for .NET d may hold a pointer to any portion of the list unless it owns one of the locks. If it only holds a local salary lock, it may not do anything except access that one data item.

As soon as the element is removed from the list (see Code Example 12-5), we can release the RWlock (no one else will ever be able to access our item). In this code, the only points of contention are:. Only one liquidator at a time may search. Only one thread at a time may give a raise to a given individual..

Something that you m ECC200 for .NET ight consider at this point is: Why not allow multiple liquidators to search at the same time, then once they"ve found the object, convert the read lock into a write lock We could modify the definition of RWlocks to allow this possibility; however, it wouldn"t work. We would have to ensure that only one thread ever wanted to make the conversion at a time, and as soon as it made that request, every other thread with a read lock would eventually have to release that lock without making a conversion request.

In other words, it"s possible to do, but it"s so limited in functionality as to be nearly worthless. For pretty much any program of this nature, design 3 will turn out to be the best. However, there are other possibilities.

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