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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 asl = 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.
Recall that condition variables are synchronization primitives that enable threads to wait until a particular condition occurs. Generalizing, the combination of locks and condit
Symmetric multiprocessing To get maximum reliability and efficiency a mode of function called as symmetric multiprocessing is used. In essence, with SMP any program or threads
List five services provided by an operating system. Explain how each provides convenience to the users. Explain also in which cases it would be impossible for user-level programs t
Define thrashing. Thrashing is the accident of high page traffic and low CPU utilization. It is observed that the cause of thrashing is an under-commitment of memory to program
a summary of what operating system do
What is a two state process model? At any time a process is being implementing by a processor or not. Therefore a process may be in Running or not running state. When an Ope
We have talked about blocking locks, which voluntarily yield, and spinlocks, which just spin until they acquire the lock. At ?rst, it seems like spinlocks are verywasteful, and tha
Write a program (with the programming language and on the platform of your choice) to demonstrate the memory leak problem (see http://en.wikipedia.org/wiki/Memory_leak for detail
Q. List three instances of deadlocks that aren't related to a computer system environment. Answer: Two cars passage a single-lane bridge from opposite directions.
Explain Formal Language Grammar A formal language grammar is a set of formation rules which explain which strings formed from the alphabet of a formal language are syntacticall
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