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3/23 3/15 OS作業
名稱	3/15 OS作業
日期	3/23
課程名稱	作業系統
指導教師	劉艾華

1.
Mutual Exclusion:
If process Pi is executing in its critical section, then no other processes can be executing in their critical sections.
Progress:
If no process is executing in its critical section and there exist some processes that wish to enter their critical section, then the selection of the processes that will enter the critical section next cannot be postponed indefinitely.
Bounded Waiting:
A bound must exist on the number of times that other processes are allowed to enter their critical sections after a process has made a request to enter its critical section and before that request is granted.

2.
If both processes try to enter at the same time, turn is set to both i and j at roughly the same time.Only one of these assignments lasts; the other will occur, but will be overwritten immediately.The eventual value of turn decides which of the two processes is allowed to enter its critical section first.

3.
Spinlocks are useful in multiprocessor systems. The advantage of a spinlock is that no context switch is required when a process must wait on a lock.Spinlocks are useful when locks are expected to be held for short times.

4.
• (1)No reader will be kept waiting unless a writer has already obtained permission to use the shared database.
• (2)Once a writer is ready, that writer performs its write as soon as possible. If a writer is waiting to access the object, no new readers may start reading.

5.
Philosopher i must invoke the operations pickup and putdown in the following sequence:
dp.pickUp(i);
...
eat
...
dp.putDown(i);
This solution ensures that no two neighbors are eating simultaneously, and no deadlocks will occur. However, it is possible for a philosopher to starve to death.

更新日期：2016/3/23 上午 11:53:03