Implementation of locks, Operating System

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.

Posted Date: 3/12/2013 5:15:10 AM | Location : United States







Related Discussions:- Implementation of locks, Assignment Help, Ask Question on Implementation of locks, Get Answer, Expert's Help, Implementation of locks Discussions

Write discussion on Implementation of locks
Your posts are moderated
Related Questions
what is a batch system give me answer in simple words so that i can understand

Q. Distinguish among PCS and SCS scheduling. Answer: PCS scheduling is completed local to the process. It is how a thread library schedules threads onto available LWPs. SCS sch


Question: (a) As a System administrator, elaborate on how you can manage computer accounts in Active Directory of Windows Server 2008? (b) Explain the following user p

Q. Explain about Operating System Services? An operating system offers services to programs and to users of those programs. It provided by one environment for execution of

What are batch systems? Batch systems are quite appropriate for implementing large jobs that need little interaction. The user can submit jobs and return later for the results.

Explain the basic method of paging method. Physical memory is divided into the fixed-sized blocks called frames. Logical memory is as well divided into blocks of the same size

File structure Certain files must conform to a needed structure that is understood by the operating system. The operating system may consist that an executable file has a parti

General Graph Directory A serious trouble with using an acyclic graph structure is making sure that there are no cycles. When links are further added to an existing tree struc

what common event leads to the creation of a process?