Thread safety, Operating System

What does it mean for something to be thread-safe? By saying that X is thread-safe, we mean that if multiple threads use X at the same time, we don't have to worry about concurrency problems. The STL, for instance, is not thread-safe; if we were to create an STL queue and have two threads to operate on it simultaneously, we would have to manually perform all locking operations. The cout instruction is also not thread-safe.

Suppose now we want to build a thread-safe queue; the methods we want the queue to have are insert(item), remove() and empty(). The ?rst question to be asked is what should remove() do when the queue is empty. One solution would be for it to return a special value (such as NULL or -1, etc) or to throw an exception. It would be much more elegant and useful, however, to make that function call wait until something actually appears in the queue. By implementing this type of blocking system, we are in fact implementing part of a producer-consumer system.

Now let us think of how to make the function wait. We can spin, i.e. write something like while (empty()) ;. This, however, obviously doesn't work, since the test of emptiness needs to read shared data; we need to put locks somewhere! And if we lock around the while(empty()); line, the program will hang forever. The conclusion is that we need some way of going to sleep and at the same time having someone to wake us up when there's something interesting to do. Let us now present several possible implementations for this system and discuss why they do not work. The ?rst possibility is:

dequeue()
lock() // needs to lock before checking if it's empty
if (queue empty)
sleep()
remove_item()
unlock()
enqueue()
lock()
insert_item()
if (thread waiting)
wake up dequeuer
unlock()

Posted Date: 3/12/2013 5:16:55 AM | Location : United States







Related Discussions:- Thread safety, Assignment Help, Ask Question on Thread safety, Get Answer, Expert's Help, Thread safety Discussions

Write discussion on Thread safety
Your posts are moderated
Related Questions

FIXED PARTITIONING Using fixed partitioning we are able to allocate the memory Here we are dividing the memory into a few fixed partitions.Every partition may not be of the si

Give a brief introduction about the operation of your program and show that you understand the idea behind threads and mutual exclusion variable. Why do we need to use mutual exclu

Q. Most WANs utilize only a partially connected topology. Why is this subsequently Answer: Cost. A completely connected network requires a link between every node in the netw

Vyvtvtn8

Discuss in detail Table management Techniques?     An Assembler employs the subsequent tables: OPTAB: Operation Code Table consists of mnemonic operation code and its machi

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

1. How is reliability enhanced with the microkernel approach to system design?  2. In a virtual machine design where guest operating systems are independent virtual machines sup

What disadvantages are there to this two-level directory? Without other provisions, two users who require cooperating with each other are hampered in reaching every other's fi

How does a program execution take place in multiprogramming? While the processor is dealing with a number of programs, the sequence with which programs are implemented will de