Distributed Systems Processes, Threads, Cde Migration分布式系统的进程，线程，代码迁移.pptVIP

CS 194: Distributed Systems Processes, Threads, Code Migration Problem Escape the curse of blocking! A spreadsheet should be able to recompute the values while waiting for user input A file server should be able to serve other clients while waiting a disk read to complete … Solutions Multi-processing Multi-threading One process + event driven programming What is a Process? Execution context Program counter (PC) Stack pointer (SP) Data registers Code Data Stack What is a Thread? Execution context Program counter (PC) Stack pointer (SP) Data registers Process vs. Thread (1) Process: unit of allocation Resources, privileges, etc Thread: unit of execution PC, SP, registers Each process has one or more threads Each thread belong to one process Process vs. Thread (2) Processes Inter-process communication is expensive: need to context switch Secure: one process cannot corrupt another process Process vs. Thread (3) Threads Inter-thread communication cheap: can use process memory and may not need to context switch Not secure: a thread can write the memory used by another thread User Level vs. Kernel Level Threads User level: use user-level thread package; totally transparent to OS Light-weight If a thread blocks, all threads in the process block Kernel level: threads are scheduled by OS A thread blocking won’t affect other threads in the same process Can take advantage of multi-processors Still requires context switch, but cheaper than process context switching Thread Creation Example (Java) final List list; // some sort unsorted list of objects // A Thread class for sorting a List in the background class Sorter extends Thread { List l; public Sorter(List l) { this.l = l; } // constructor public void run() { Collections.sort(l); } // Thread body } // Create a Sorter Thread Thread sorter new Sorter(list); // Start running the thread; the new thread starts running the run method above // while the or