Why Thread?

Here is a quick brief about a concept of thread. Thread is a light weight process, it takes less time to create, context switch or destroy thread than a process. We want simultaneous activities for a better interraction with a user or take advantages of multi-processors to archieve a maximum system resourse utilization.

For instance, in word processor, one thread responses for I/O, while another is doing a grammar check. Now, lets take a look at a simple JAVA program to see how the thread create, run, and how threads assignment work in JAVA.


public class thread extends Thread{
public void run() {
for(int i = 0; i < 10; i++) {
System.out.println("Child thread " + i);
}
}

public static void main(String[] args) {
thread t = new thread();
t.start();

for(int i = 0; i < 10; i++) {
System.out.println("Parent thread " + i);
}
}// end main
}// end class thread

In the code above, we created two threads. When the new thread create, it will go to the run() method and do the job, so we can see from the output from the program that there will be two threads execute concurrently.

program output:

Parent thread 0
Parent thread 1
Child thread 0
Parent thread 2
Child thread 1
Parent thread 3
Child thread 2
Parent thread 4
Child thread 3
Parent thread 5
Child thread 4
Parent thread 6
Child thread 5
Parent thread 7
Child thread 6
Parent thread 8
Child thread 7
Parent thread 9
Child thread 8
Child thread 9

Microsoft DreamSpark Gives Free Software to All Students

“Microsoft gives students access to technical software at no charge to inspire success and make a difference”
I just read a forward email from my Professor and found that the email is interested. Yes, Microsoft has been pushing theirs products to students to get used to their softwares, so that many of the students will most likely work with MS products after they graduated. This includes MS Visual studio, Window 2003 server and so on. In my opinion, these softwares are too expensive for student to own, approximately 300$ each?, so most of the students take alternate way by going to open sources or illegal softwares.
Microsoft already has the MSDN Academic program which is supported only specific universities. Now, It seems to me that they are distributing for all the student around the world by having a verification system such as International Student Identity Card (ISIC). This card will become a standard for student to be able to download their software properly. Here they comes, another strategy. For those who would like to read more about DreamSpark, you can follow the following link, https://maroon.cudenver.edu/webmail/services/go.php?url=https%3A%2F%2Fdownloads.channel8.msdn.com%2FFAQ%2FStudents.aspx.

A Dynamic Data Race Detector for Multithreaded Programs

Eraser: A Dynamic Data Race Detector for Multithreaded Programs, by Stefan Savage, Michael Burrows, Greg Nelson, Patrick Sobalvarro, and Thomas Anderson, ACM Transactions on Computer Systems, Vol. 15, No. 4, November 1997, pp. 391-411.

According to the paper, Erase: A dynamic Race Detector for Multithread Program, the authors claim that dynamic data race is hard to detection, so programmers are suffered when programming by using thread. There are already work that solving about the data race problem from Lamport’s happen relation, however, it costly so they would like to introduce a new method. These are the main motivations of the author regarding to the paper.

The authors contribute by introducing a dynamic race detection tool which is called “Eraser” this tool will monitor the program when it reads and writes when it executes, they state that the tool is more effective and un-sensitive than manual debugging. Another important of the main contributes of this paper is a Lockset algorithm, which will use to detect the data race in multithread programs.

Moreover, about the Eraser detection program, the program can detect race condition in Operating Kernel. For their experiment, the authors test Eraser on the real programs and applications. the HTTP server and indexing engine from AltaVista, the Vesta cache server, the Petal distributed disk system and various programs from programming assignment from students. However, the author is not concerned about its performance due to the high overhead. However, but the authors believe that it is fast enough to debug most of the programs and focus on the false alarms of the program when it found the data race.

The most efficiency of this paper is that the program Eraser cannot prove that the test program is race data free. Also, checking for dynamic data race is impractical. The experiment methods should cover most of the operating systems that we use these days and various of programming language should be tested instead of having only C++ programming language. Moreover, the use of the Eraser program should be describe for the audience, so they can know how the program works out for each test programs. The graph and performance should be provide instead of describing what happen for the program they run on.I would rate the significant of this paper 4/5(modest) due to the challenge topic and idea.

Scalable Threads for Internet Services

Capriccio: Scalable Threads for Internet Services, R. V. Behren, J. Condit, F. Zhou, G. C. Necula, E. Brewer, Proc. of the Nineteenth Symposium on Operating System Principles (SOSP-19), Lake George, New York. October 2003, pp. 268-281.

Thread-based versus event-based programming has been a popular topic recently. For this paper, the authors have shown a strong motivation and contribution such as developing a scalable thread packet for use with high-concurrency servers which is called Capriccio.

The authors have noticed a lot of disadvantages of using event-based programming. For instance, the “stack ripping” where programmers have to save and restore live state is too complicated to use. The authors believed that by using thread-based could make life easier and could also achieve high currency just like the event-based programming as well.

In order to make thread-based model to be better than event-based model, they have build the thread package under the user-level threads, due to the fact that the user-level thread have more advantages in term of performance and flexibility over the kernel one. The implementation of Capriccio is amazing such that we don’t have to modify our applications to be able to use features from the thread package. Capriccio uses and takes advantages of new mechanisms from the latest Linux for its synchronization, I/O and Scheduling mechanisms. This is the reason why the result from the benchmark which they showed in the paper is surprisingly good for thread creation, context switch and so on; it is faster when comparing to the original Linux threads and the others comparators.

The idea of introducing linked stack management, resource-aware scheduling, blocking graph and modify some algorithm are surely improve the system utilization. Base on the performance from their evaluation which they compare between the default web servers such as Apache, Haboob, the results looks realistic. Because of the benchmarks they use are the real world application, and the Capriccio performs very well for both scalability and scheduling.

However, we already know that there must be some disadvantages of using thread-based model. One of them which I am very concerned is the issue when having multiple processors for both homogeneous and heterogeneous chip types. The authors mentioned the drawback of user-level threading such that it could make it more difficult to take advantage of multiple processors. As we know, SMP (symmetric multiprocessing) or CMP (chip multi processor) like Intel duo core has been increasing in the computer market these days. I wonder if the thread-based model will take advantages of having multiple processors more than the event-based model or not. What if we try to fix both user-level and kernel level threads instead of employ only the user-thread level. The future work section in the paper doesn’t give much detail regarding to the issue.

Lastly, I would rate the significant of this paper 5/5 (breakthrough) because they have use and modify many mechanisms and creating a new thread packet to show us that thread-based programming is better to use for high-concurrency internet servers. Their dedication and ideas are impressive

Why Events Are A Bad Idea

According to the paper, ‘Why Events Are A Bad Idea (for high-concurrency servers), R. Behren, J. Condit and E. Brewer, Proceedings HotOS IX, Kauai, Hawaii, May 2003, pp. 19-24.’ As we know, thread versus message passing(event-based) programming has been debating in term of which is the best in term of performance lately, and many people believe that the event-based programming is much better in many ways than thread programming. In the paper, the main motivation of the authors is to show that thread programming is better than event-based programming in highly concurrent applications environment. They have shown us that thread could perform about the same as event-based in many criticize cases and it could have done better if we have fixed the complier. In other hand, they have concluded that thread will outperform event-based programming by judging from their analysis from the simulation they built. For this review, I will explain the authors main contribution, theirs deficiency. Lastly, I will rate the significance of the paper based on my personal opinion.

According to the paper, the authors has shown us the different between events and threads in term of their responsibilities such that events use event handlers and send /wait for messages, while threads use the function forks and so on. They also describe the problem with threads which has been criticism from other who think that event-base does better, such as performance, control flow, synchronization, state management and scheduling. They proved that these problems caused by the implementation of the programmers.

To make us believe that thread could perform better than event-based, they points of the two important properties of why thread could do better. For example, in modern servers, the requests from the client are independent, and the code which handles the request is sequential. So, they came up with the experimental by modify the compilers and integrate the complier and runtime system. Moreover, they ran the simulation and analyze the results such that event-based requires too many contexts switches and use too much heap due to the fact that its execution is so dynamically. Therefore, they conclude that the thread avoids this kind of problem and could give us a better in execution time.

In my opinion, I think the deficiency is that they haven’t done enough experiments with other cases such as they could test on other operating systems, or by using other benchmark suits to test on various inputs before they conclude that the simple thread programming perform better than the event-based one. However, thread versus message passing is an interesting topic, but in term of practicing in real world applications, it would cost so much time and afford to modify or integrate the complier and runtime like they mentions in the paper. Finally, what if their future results show a big advantages of thread and huge different in term of performance between them, but in reality many programmers still don’t quite understand how the thread really work, so are we going to achieve the utilization of the computer resource we have? I would rate the significance of this paper 3/5 because of the lack of evidences in term of real-application and the lack of references from others research which support the author’s arguments.