share memory（共享内存）.doc

share memory（共享内存） Posted on 2010-07-28 17:53 Oracio Oracio reading (171) review (0) edit collection Last week, the tutor assigned a small program to familiarize us with the programming methods of Shared memory on Unix. The topics are briefly described below: Design a C/S structure of the program, the opening of a Shared memory read and write procedures, server side is responsible for writing data (every time to write a length of 100 arrays), the client side is responsible for reading data, and the elements of an array of 100 to the TAB character segmentation of the output to a file. The synchronization of data read and write without any locks and semaphore is not used (the client will not be able to read the server when it is assigned to the element in the array). Solution: First of all, in the case of unlocked, for synchronous data read and write, Shared memory how to apply for an int variable, as a symbol of data read and write access bits (0 - free, producers can write at this time, 1 - busy, both can not access, 2 - new data, the consumer can read); The Server/Client should first modify the flag bit to tell the caller that they want to manipulate the data, but the other person is waiting. Two programs with normal, Server/Client see Shared memory in the process of the first address is different, because the operating system for each individual run its own process space program distribution, process space with a address, each process can only be run and operation of that address space that assigned to him, and cannot be accessed across processes address (for security reasons); And Shared storage is also the purpose of each other in order to make this process can share data, the kernel will alone create a space for Shared storage space (independent of any process), and hooked up to the Shared storage process will share the physical address space mapping to its own address space, the process of access to a Shared space, and access to their own space, but also beca