Implementation of locks, Operating System

Assignment Help:

How could we implement locks? No matter how we choose to implement them, we must have some hardware support. One possibility for implementing locks on a uniprocessor machine is is to disable interrupts when testing/setting locks. With interrupts disabled on a single processor machine, the processor cannot switch processes, and so we can guarantee that only the active process will have access to the shared data. Another option would be to make use of atomic operations, such as test and set. This type of operation (which usually corresponds to a single atomic assembly instruction) behaves as if it used the following C function, atomically:

int test_and_set(int x) // let x be strictly either 0 or 1.
{
if (x) { return 1; } else { x=1; return 0; }
}

All this needs to be implemented atomically, in hardware. Using this type of atomic operation, one could implement thread lock(l) simply as while test_and_set(l) {

; // do nothing
} // spinlock version of thread_lock()
and thread unlock(l) simply as
l = 0; // we need this to be an atomic clear (or assign) instruction

The assembly instruction test and set can bemade to be atomic acrossmultiple processors. An equivalent option would be an atomic compare and swap assembly instruction. These low-level hardware solutions are then built up into high-level functions, either built into the languages, or in libraries. In general, do not implement your own locking functions, but rather use functions from a tested library. Getting things right can be tricky, and your own solution is also likely to be non-portable.


Related Discussions:- Implementation of locks

What is virtual file system?, What is virtual file system? A Virtual f...

What is virtual file system? A Virtual file system switch (VFS) or Virtual file system is an abstraction layer   on top of a more concrete file system. The purpose of a VFS

Semaphores, Synchronization can be achieved by means other than locks and c...

Synchronization can be achieved by means other than locks and condition variables. One alternative is semaphores. A semaphore is used to regulate traf?c in a critical section. A se

Nested Macro calls, . Nested Macro calls are expanded using the

. Nested Macro calls are expanded using the

What is belady anomaly, What is Belady's anomaly When plotting on a g...

What is Belady's anomaly When plotting on a graph the page faults versus the number of available frames. We notice that the number of faults for four frames is greater than th

What is two-level directory, What is Two-level directory In the two-lev...

What is Two-level directory In the two-level directory structure every user has own user file directory (UFD). When a user jobs begins or a user logs in, the system's master fi

Safety algorithm and resource request algorithm, Safety algorithm : This is...

Safety algorithm : This is to make sure if the system is in safe state or not. It may need an order of m x n2 operation to determine if the state of the system is safe or not.

What kernel provide for an effective user level thread, 1. What must a kern...

1. What must a kernel provide for an effective user-level thread implementation? 2. With respect to the quantum q in a scheduling algorithm, explain and discuss the impact of th

Explain briefly the working of semaphore with example ?, Explain briefly th...

Explain briefly the working of semaphore with example ? The E.W. Dijkstra (1965) abstracted the key idea of mutual exclusion in his concepts of semaphores. Definition A s

Explain fifo page replacement in detail, FIFO page replacement This is...

FIFO page replacement This is the easiest page replacement algorithm. Here the 1 st page toward the inside is the 1 st to leave that is the oldest page leaves. To execute th

What is the lower bound on the numeral of page faults, Q. Presume that you...

Q. Presume that you have a page-reference string for a process with m frames (initially all empty). The page-reference string has length p along with n distinct page numbers

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd