聊城大学计算机学院计算机操作系统（2）英文课件 Lecture5.ppt

CS162Operating Systems andSystems ProgrammingLecture 5Cooperating Threads September 14, 2005 Prof. John Kubiatowicz /~cs162 Review: Per Thread State Each Thread has a Thread Control Block (TCB) Execution State: CPU registers, program counter, pointer to stack Scheduling info: State (more later), priority, CPU time Accounting Info Various Pointers (for implementing scheduling queues) Pointer to enclosing process? (PCB)? Etc (add stuff as you find a need) OS Keeps track of TCBs in protected memory In Arrays, or Linked Lists, or … Review: Yielding through Internal Events Blocking on I/O The act of requesting I/O implicitly yields the CPU Waiting on a “signal” from other thread Thread asks to wait and thus yields the CPU Thread executes a yield() Thread volunteers to give up CPU computePI() { while(TRUE) { ComputeNextDigit(); yield(); } } Note that yield() must be called by programmer frequently enough! Review: Stack for Yielding Thread How do we run a new thread? run_new_thread() { newThread = PickNewThread(); switch(curThread, newThread); ThreadHouseKeeping(); /* Later in lecture */ } How does dispatcher switch to a new thread? Save anything next thread may trash: PC, regs, stack Maintain isolation for each thread Review: Two Thread Yield Example Consider the following code blocks: proc A() { B(); } proc B() { while(TRUE) { yield(); } } Suppose we have 2 threads: Threads S and T Goals for Today More on Interrupts Thread Creation/Destruction Cooperating Threads Interrupt Controller Interrupts invoked with interrupt lines from devices Interrupt controller chooses interrupt request to honor Mask enables/disables interrupts Priority encoder picks highest enabled interrupt Software Interrupt Set/Cleared by Software Interrupt identity specified with ID line CPU can disable all interrupts with internal flag Non-maskable interrupt line (NMI) can’t be disabled Example: Networ